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js530
06-28-2006, 12:46 AM
Since someone asked for it, here's my project log of building a TIG welder from the ground up (not from a stick welder). Three transformers provide 20 volts each, at probably 50 amps each. I'm going to need to install a 240 volt outlet if I really want some power, the power factor on the transformers (rewound microwave oven transformers) is pretty bad. So far I've tried the transformers and the HF/HV starter, but not together (need a cap for a low pass filter to prevent HV entering the transformers. Power control is provided by a phase angle control, two anti-parallel SCR's (while essentially a triac, triacs have problems with inductive loads, sometimes they dont turn off at zero crossing). Pictured is a triac, although im going to the surplus store tomorrow for the biggest scr's they have. Tig torch is WP17V, with valve.

Some pictures

MT1 broke off the triac

js530
07-04-2006, 01:39 AM
No pictures on this update, but I did find a very large fan for the triac, and some emi suppression caps for adding HV. Also bought four 70 amp diodes, which will do until i can find some stud mounted ones on ebay. All together, less than $20.

2muchstuff
07-04-2006, 01:47 AM
Do you have a wiring schematic for this. I bet I could scrounge up most of this.

Hamadamj
07-04-2006, 04:11 AM
Very interesting !

sanddrag
07-04-2006, 04:35 PM
I'd like to see a bead you've layed with it.

js530
07-04-2006, 05:41 PM
I'd like to see a bead you've layed with it.

When I do start welding, I don't think it will be pretty. I've never welded tig or even OA, so don't expect anything great.

Schematics are in pdf and dxf

diarmaid
07-04-2006, 06:21 PM
Wheres the thread on your DIY Plasma Cutter? :)

js530
07-06-2006, 01:30 AM
Some new pictures. Sorry people on dialup (~2mb)

24-The welder on a prototype case. The "case" is pretty much non existant until I get the plasma cutter working (tin snips are painful)

25-The arc starter, only the transformer has been mounted. It's a 9kv/30ma unit, so it probably needs a seperate circuit from the welder (rated 240va)

26-The front plate, incl. circuit breaker and current adjustment pot (which is unconnected)

27-HF suppression caps, to prevent the power stage from being destroyed by the arc starter

28-A large 120 vac fan

29-The starter tank mmc, aren't those caps familiar?

30-Adjustable Spark gap, a 10-32 screw will clamp the electrodes (tungsten) in place

33-Poor man's HV wire, just some clear plastic tubing around a 600v rated wire

34-Heat sink compound

35-Triac next to triggering diac on top of a big heatsink

Does anyone have an suggestions on how to flatten aluminum sheet? It's bent out of shape from the tin snips, and I can't seem to get it flat again.

vulcom1
07-06-2006, 09:48 AM
I am also very interested in your work. It would be nice if you could put some size and values of the components in your pdf file. With the rewound transformers the voltage and wire guage also would help.
Thanks, John

js530
07-21-2006, 03:40 PM
The HF suppression caps are rated .047uf 1600 vdc, 900 vac with 5 parallel sets of two in series, giving a .235 uf 1800 vac bank of capacitors. Secondaries are ~22 volts, using around 20 turns of 16 ga plastic insulated (non magnet wire, much cheaper) wire. The tank cap is around 30 of the same .047uf caps in series.

I'm pretty sure I need a better power control circuit than what I have, so the details on that will come later.

diarmaid
07-22-2006, 01:26 PM
Great work. Its certainly coming together. :)

js530
07-23-2006, 11:16 PM
I finally had a chance to run both the arc starter and welder, and am slightly disappointed. There's two issues:
First, the plastic holding the spark gap pretty much caught on fire. There is a fairly easy fix, move the gap to the exact center, and if necessary, add a fan (would also provide some arc quenching=better performance)
Second, and more importantly, the arc would not sustain full power. Without a capable amp meter, I can only guess the cause. I have a feeling the transformer (I'm running only a single transformer to prevent tripping the house breaker), is saturating. The HV arc would stay on the entire time, but the high current arc would only be sporadic, despite the arc distance. I'm going to run it again tomorrow with the second transformer running off a different branch via an extension cord, and see if I can't get an arc to sustain. But it was definately a welding arc.

Edit:
After some reading, I realized saturating a transformer is impossible by excess secondary current draw (it's dependent on voltage and frequency only (chair)) I guess my next option is the second transformer, maybe in series.

js530
08-08-2006, 12:00 AM
Sorry for the long wait, but there's some good news....

It works!!!!!

The 25 amp circuit breaker (the one on the aluminum front panel) kept tripping, which might be a good thing depending on how you look at it (3kw of power...). It would start an arc at about 1/2" away from the workpiece, which caught me by suprise a few times. I could weld for about 5 seconds before the breaker tripped, which may explain why the puddle just looks like a blob of metal. I also think the shielding gas flow rate was too slow, or the electrode was too far out of the cup.

Tomorrow I might try using two seperate 20 amp outlets with an extension cord, and without the 25 amp breaker.

Now does anyone have some 100+amp diodes? :p

js530
08-08-2006, 11:55 PM
A few more pictures

It seems the filler doesn't really want to stick to the aluminum. Is this caused by surface oxidation? The duty cycle is fairly low, even with a fairly large fan on it. I'm going to see if some secondary side ballasting can help limit current.

I'd really like to see how it compares to a real tig welder. The closest to a bead I could get was the bottom of the first picture. As soon as the puddle develops, the surrounding aluminum starts melting. I'll try again tomorrow. I only tried to lay a bead on aluminum because I don't have big enough diodes for steel.

(The switch on the torch controls a relay which controls the HF starter)

lwill
08-09-2006, 12:09 AM
What shield gas are you using and what type of tungstun?

js530
08-09-2006, 12:15 AM
What shield gas are you using and what type of tungstun?

Straight argon and pure tungsten (green). HF was on the entire time, aluminum is unknown extrusion alloy. Filler is 4043.

miljnor
08-09-2006, 12:33 AM
all that is good but it looks like you could use a little cleaning on the aluminum.

Aluminum to get a good weld must be very clean. And depending on the amperage/voltage used you might have to preheat the metal to get a good weld started.

If youve never welded before aluminum isn't the best thing to start on and definitely not on a rigged up welder.

just my 2cents

lwill
08-09-2006, 12:37 AM
The oxidation on the AL can definately be a problem, ANY contamination on AL make it more difficult. Best thing to do is wire brush it just before you weld with a stainless steel brush. (normal steel one will leave residue as well) Even with it very clean, starting a bead is tuff if you have never done it. You will see the surface turn dull, this is the remaining oxide on the surface of the molten puddle. You have to stick the filler rod into the puddle to break this surface. Once that is done the bead will form much easier because the fresh metal is inside the sheld gas area and will not oxidize as fast. Another thing that can cause problems is the fact that AL conducts heat so well that if is laying on a steel table it could be soaking up the heat. It looks like you are useing a very thin piece so this may be to your advantage to keep from mealting the whole thing. Very large peices of AL you need to preheat before welding to get a good joint.
I failed to pay attention to your earlier posts, are you using AC or DC? AL needs AC if you are using argon or argon/helium mix to help "scrub" the oxide away. If you are using DC you can use pure helium I am told. (never tried it myself) Steel needs to be welded using DC with ground on the work peice. 2% thoriated(sp?) "red" tungsten will give you a better weld and last alot longer on steel but will contaminate aluminum.
I hope this info helps, good luck! Keep on posting!

js530
08-09-2006, 01:05 AM
I failed to pay attention to your earlier posts, are you using AC or DC? AL needs AC if you are using argon or argon/helium mix to help "scrub" the oxide away. If you are using DC you can use pure helium I am told. (never tried it myself) Steel needs to be welded using DC with ground on the work peice. 2% thoriated(sp?) "red" tungsten will give you a better weld and last alot longer on steel but will contaminate aluminum.
I hope this info helps, good luck! Keep on posting!

I'm using AC, which is why I tried aluminum. I also tried to tack weld two ~14 ga pieces of aluminum sheet. I noticed it seemed to only heat one at a time, and both failed to stick together. There was a slight gap between the plates, but it wasn't more than 1 mm. I didn't brush the surface, so that might have something to do with it.

I've welded aluminum with my mig welder, but that was an excercise in frustration. I probably should've used a teflon gun liner, but never bought one.

I definately need a better way to cool the transformers. Oil cooling would be an option, except the whole flammability issue.

lwill
08-09-2006, 01:27 AM
You definately have to use filler rod with aluminum to break the surface and get them to stick. You cannot "tack" or fuse aluminum together like steel. Once the puddle starts on one piece it will help the heat flow to the other, sort of like tinning a soldering iron. The heat flows with the arc and both will take the path of least resistance. Once the puddle starts you can help control how hot it gets (since it looks like the variable peddle is a bit in the future for you! :) )by adding rod faster or slower.
I am far from a pro at TIG, but fake it pretty good and have been lucky to use good Miller and Lincoln machines (and had good teachers). I feel for you learning on a machine when you are not even sure if is working right. If you get a chance, try out a real machine so you can tell better what is wrong. I'll give what advice I can if you ask.

Corvus corax
08-13-2006, 10:51 PM
You will probably find it relatively impossible to weld aluminum. Even with a proper TIG setup it requires a fair amount of time to get the technique down, and consistency even longer. I would concentrate next if I were you on making the welder operate on DC. AC welding with TIG works well once you are able to unbalance the waveform to the negative side, as the balanced waveform you currently have will overheat the tungsten in short order. Positive polarity with respect to the workpiece sends about 80% of the heat to the tungsten due to ionic bombardment. In any given arc, the anode always gets hotter. Welding steel is a doddle compared to welding aluminum- about half the heat input required, because steel is a very poor conductor of heat away from the weld pool. You can weld it fine with an AC waveform as well, but AC waveforms are difficult to control unless you have fast zero crossing electronics built in to your welder. The arc typically extinquishes during the zero crossing event, unless your using SCRs and two seperate DC supplies, to speed up the switching time. Otherwise, you will be using HF the whole time to keep the channel open. With DC, you don't even have to use HF start, simply lift or scratch start the arc.

Also, thoriated tungsten is fine for aluminum- I've used it for years for that purpose, and stopped using pure tungsten long ago. You'll find 2% is far more durable for a given tungsten diameter, and arc starts are superior. Lanthanated is better for aluminum, but it is harder to find here in the states. And if you haven't already, get yourself an ARC welding helmet, or you'll find that "sandy" feeling in your eyes getting worse. :) If you haven't experienced the delights of arc flash in your eyes, or on your skin, I'd be surprised. That goes for plasma cutting too, especially on aluminum. It takes about fifteen or twenty seconds of arc time using my welder at 200A on aluminum to induce a burn on any exposed skin similar to what one would get after a full hour in the Florida sun. Wear a long sleeved shirt. Medium wave, short wave, and vacuum ultraviolet is produced in PRODIGIOUS amounts by these machines. The acrid smell while working a TIG isn't from the arc, its from the UV light produced, powerful enough to rip the oxygen molecules in the air apart, producing monatomic oxygen, ozone, and nitric acid.

motomitch1
08-14-2006, 12:02 AM
surface oxidation needs to be cleaned off before you try to lay a bead.

it takes less amperage to tig weld steel so you could use smaller diodes for steel

js530
09-26-2006, 10:34 PM
And if you haven't already, get yourself an ARC welding helmet, or you'll find that "sandy" feeling in your eyes getting worse.


I've been using a helmet (for mig), just the whole arc-starting-away-from-the-workpiece thing has caught me by suprise a few times.



The acrid smell while working a TIG isn't from the arc, its from the UV light produced, powerful enough to rip the oxygen molecules in the air apart, producing monatomic oxygen, ozone, and nitric acid.


And, in my case, the spark gap. Running for just five seconds with the garage door shut produces a noticable smell.

Some conclusions...

I've been experimenting with the "welder" for a few hours, and it's just not very practical. Two MOT's have died (I believe heat related causes), and about the only thing I can weld with one mot is some 16 ga steel. The starter works perfectly, maybe even too good (or is it "too well"...?). Is it normal for an arc starter to allow arcing ~3/4" away from the workpiece?

So yes, it is possible to build your own TIG welder, but it's much easier/reliable/useful to find a used stick welder, and add a torch and starter. Which is exactly what I'm going to do next. Now does anyone have an old stick welder in the DFW area? :p

dumaster
10-27-2006, 10:59 PM
So yes, it is possible to build your own TIG welder, but it's much easier/reliable/useful to find a used stick welder, and add a torch and starter. Which is exactly what I'm going to do next. Now does anyone have an old stick welder in the DFW area? :p

hello js530

I found this project very interesting, I have a stick welder , it wanted to
know if I to rectify it, and to make the high-voltage circuit, I will be able
to use it as a TIG ?

Another one doubts is if the high-voltage can be used to stick welder,
and as it is the construction of the Coupling Transformer, it would
like to construct one!

I wait a return !!

Best Regards

Eduardo

dumaster
11-01-2006, 10:30 PM
it has some friend to help me here in the questions above ? ^^^^^^^

Ed VanEss
11-02-2006, 12:36 AM
alum is fussy,must be very clean -clean with stainless brush. concintrate your heat on the part. When it starts to look wet, add wire. always keep the wire in the shielding gas,[near the cup]- use argon gas @ 20psi. tungston-use .093zirconium or pure. try 4043.o62 wire. Lot of welders use to big of wire, which is fine on heavier parts. Tungston should only stick out of cup the di. of the tungston, unless using a gas lens. must be set on ac with continuos HF. you might be better off practicing on steel. its a lot easier for starting out. for steel, use 2% thirated tungston.093 di. sharpen to a clean point. dc current 15psi argon .HF only for starting. should also have a post flow on the shielding gas to keep the tungston clean as it cools, [about 3-5 seconds]
Practice-Practice-Practice

crease-guard
11-11-2006, 06:50 AM
All of the above advice is spot on and is worth a semester in welding class just reading.

I have a ThermalArc 185 unit in my garage I use for welding aluminum and what not. My welding prof told me that in order to get a good weld (in addition to all the things mentioned previously) you needed to put a lot of heat into the initial arc to create a puddle as quickly as possible, then add the filler in as mentioned before and start moving. As you start to create a longer bead...you're heating up the aluminum even faster and the puddle will start to widen because you now have too much heat in the puddle. You need to use your foot amptrol to back off on the current or you will burn through the alumium. You'll also start to warp longer pieces if you run beads too long, so you need to tack at multiple spots and run shorter beads to keep the metal from warping.

Aluminum is a bugger to weld. More an art than a science. but even for me, I've gotten OK with my aluminum welding.

Jay

Ed VanEss
11-11-2006, 02:28 PM
when welding alum , do NOT mash the pedal to heat the base metal quickly. to much amperage will cause the tungston to spit particles into the puddle. Let the base metal heat slower, and you will have less problems. I had one of the first Miller tig welders around. No foot pedal, and had to crank the amperage to your preferance. That was over 30 years ago.

ozzie34231
11-11-2006, 03:02 PM
Hi All,
Would someone spell out what has to be done to a stick welder to get to TIG. Will I spend more than buying a TIG. Since I bought a small Mig unit I haven't used mine. I've welded a lot of metals with the Mig but it just doesn't seem hot enough for Aluminum; wire just sticks, and the wire feed of aluminum is a nightmare. I'm retired so I have plenty of time, I think ;-)
Thanks,
Jerry

Ed VanEss
11-11-2006, 09:48 PM
Years ago Sears made a high freq attachment for a stick welder, which I tryed. Took it back and bought a miller. The problem with a stick welder is it must be both AC-DC. There's quite a few used tig welders out there now days. so be better off looking around, or check with a dealer. The problem with a mig for alum is the wire bends pretty easy, pushing the wire through a 12 or 15 foot cable, so a spool gun is the way to go there, but if you want to weld up some neat looking alum projects, you can't beat TIG.
A stick welder is obsolete these days, if you really need stick, you can do it with your tig. look around for a used Miller 250 Dial arc. I,ve had one for 20 years, and as far as I'm concerned, it's bulletproof.
Hope I was of some help.
Ed V

diarmaid
11-13-2006, 05:36 AM
Hi All,
Would someone spell out what has to be done to a stick welder to get to TIG. Will I spend more than buying a TIG. Since I bought a small Mig unit I haven't used mine. I've welded a lot of metals with the Mig but it just doesn't seem hot enough for Aluminum; wire just sticks, and the wire feed of aluminum is a nightmare. I'm retired so I have plenty of time, I think ;-)
Thanks,
Jerry

How 'small' exactly is your Mig ?

From my limited knowledge, a spool gun is a good idea, perhaps essential. If you want more heat with your Mig crank up the volts and reduce the wire speed.

Mortek
11-17-2006, 12:33 AM
Here's a sample of a project I am "currently" welding. Done with a Miller Syncrowave 350 LX
2" diameter 6061 aluminum tube 1/4" thick. About 250 amps 3/32" 4043 rod

diarmaid
11-17-2006, 03:23 AM
Nice welds Mortek

ninefinger
11-17-2006, 09:03 PM
Hi All,
Would someone spell out what has to be done to a stick welder to get to TIG. Will I spend more than buying a TIG. Since I bought a small Mig unit I haven't used mine.

If you're electronically inclined I found a guy who did make his own TIG, and he did it right - variable everything. His design requires only a low voltage high amperage power source (like those "obsolete" AC stick welders).

I've started thinking about his design and have started to make a parts list for Digi key - so far I'm at ~ $160 for parts - probably need another $60 or so by the time I get all the little things added on.

Add a Stick welder for ~ $250 and a ton of shop time (...which I don't have)

http://www3.telus.net/public/a5a26316/TIG_Welder.html

Mike

diarmaid
11-18-2006, 07:04 AM
Wow! Thats such a great link. Thanks ninefinger.

Wish there were more comprehensive instructions though, as I dont have the knowledge to make something just from his electronic diagrams. Definately an experiment/project for the future. :)

s_c_engineering
02-16-2007, 11:24 AM
your welder would work a lot better if you put the magnetic shunts back into your transformers, that would get tid of the overheating/frying the mot problems, you should also be using around 10awg wire in those transformers. what size microwaves were those transformers out of?

tadream
02-24-2007, 06:17 PM
your welder would work a lot better if you put the magnetic shunts back into your transformers, that would get tid of the overheating/frying the mot problems, you should also be using around 10awg wire in those transformers. what size microwaves were those transformers out of?

That was something that I wondered about myself. I don't know much about microwave transformers, but I was wondering what kind of a volt-amp curve they have. You need a fairly high open-circuit voltage, but it needs to 'droop' pretty sharply while providing plenty of current. This is the difference between stick/tig and Mig power sources. Mig is Constant Voltage, stick & Tig are constant current. All this means is that the mig transformer is more closely coupled than the tig. It tries to maintain it's output voltage while allowing the current to vary considerably to do so. Tig is the opposite. It tries to maintain it's amperage, while letting the voltage vary widely to do so. Part of your description kinda sounded like the transformers might have too much of a 'CV' behavior. Also, yes, your Alum was much too dirty to achieve a good weld, and aluminum tig takes a good bit of practice to learn. Once you have a puddle going you have to MOVE with it, or your puddle will quickly end up in the floor :D. As to the questions about stick/tig, the older (pre-squarewave) machines are just stick transformers with the HF circuit added to them.

D_ego
03-05-2007, 12:42 PM
Hello I made a table to weld (GTAW) to drive a high frequency equipment. the equipment works well but when the arch is created the engines don't work, i want to know why. I am working with a kit xylotex of 3 axes.

forgive my english

venomx999
03-07-2007, 11:06 PM
what a crazy creation! if it cost less then its feasible to play with this project...but from what I heard it cost more than an actual machine..lol
Maybe its great for someone who has tons of cash to waste. Until someone comes up with simplier machine where the parts can be found in electronic dumpsters, it is looking like a government funded project lol.

venomx999
03-07-2007, 11:15 PM
I was referring to the link on this post to another project ..not this one. Srry for the confusion lol

punisher454
09-11-2008, 02:44 AM
Okay, my first post here. I am in the process of building a variable square wave tig, somewhat inspired by the link earlier in this thread.
I am using:
16 70A IGBT's
10 35A full bridge rectifiers
some doorknob Cap's
a 225A AC arc welder
some TSV diodes
and various small electronic components.

Unlike the machine in the plans, I am using an AVR microcontroller to drive the IGBT H-bridge.
Parts are in the mail on their way here now, but I am still trying to decide what to do about the HF spark gap and the HF coupling transformer. Would a spark plug be okay for a spark gap? and what diameter and number of turns would be best for HF-coupling with a Neon x-former?
so far my digikey bill is around a hundred bucks, the Igbt's were around $60 or so and the rectifiers were about 25 bucks. I priced the same parts out about 4 years ago and it was almost three times the price.
I'll post here on the "zone" with my progress in the coming weeks.

MrWild
09-14-2008, 12:26 AM
EXCELLENT! I'll be looking forward to reading your posts.

thkoutsidthebox
09-14-2008, 06:25 AM
I'll second that! :) Pics are always very welcome.

punisher454
09-15-2008, 02:33 PM
I am working on several projects at the moment, but this one is very high on my list. In the coming weeks I'll document my progress and start a new thread with pics, parts lists and all. Microcontroller source code will also be posted.

marcgvky
12-08-2008, 11:54 AM
Punisher, any word on your success?

Sorry for the icon on my subject line, I thought that was a "Question Mark" now that I look at it, it's a thumbs down. Not my intention, just bad eyesight :-(

punisher454
12-09-2008, 04:28 AM
Punisher, any word on your success?

Not yet, I have most all of the parts, just need a little time to work on it. Soon I hope.

integerspin
12-11-2008, 10:29 PM
I don't know if it would be any use but I have a schematic for my tig?

Spark plugs are fine.

iEdd
12-25-2008, 02:22 AM
Yes, please post your schematic if you have one, and pictures are great too. I am about to start a project like this myself (stick to TIG conversion).

Edit: Any ideas for a suitable enclosure for the HF unit and solenoid? Preferably on the cheap. Metal would be nice, but could be a pain to insulate.

OrionBlade2003
12-26-2008, 01:42 AM
Spark plugs - USE NGK SPARK PLUGS!!!

They don't have a resistor in them, so you won't trim your signal to the tune of 100-300 ohms.

They do that for non-race plugs since it helps attenuate RF hash, but you should be able to use the non-resistive plugs without a noise problem. It is a TIG welder, after all!

Also, the resistive plugs may or may not, depending on your pulse forming network (sounds like a marx bank) blow up your circuit with reflected pulses/ringing.

Been a while, but I worked at a pulsed power lab, and blew up quite a few 120 dollar IGBT's and cascade Mosfet's.

*sigh* them were the days. Blow up parts and learn stuff on someone else's dime!

iEdd
12-26-2008, 01:48 AM
Spark plugs - USE NGK SPARK PLUGS!!!

Uh... ****. I bought "resistor type" Champion spark plugs on eBay.

Will all NGK spark plugs work? I assume I need 4 of them.

OrionBlade2003
12-26-2008, 02:26 AM
in the spark gap circuit is the spark gap and a capacitor you should be fine as far as not blowing things up, but you'll be trimming your signal, which is kind of a waste, and the plug will heat up eventually, limiting duty cycle (or it'll blow up...)

Virtually all NGK race plugs will do it. Not sure why you need 4 spark gaps?

didn't read the whole thread, but I used plugs as spark gaps before, and figured i'd drop in my $.02

The most critical part of a spark gap is just that, the gap. You can make your own if you want, just use, ironically, two pieces of tungsten welding electrode. You would want the electrodes pointing at one another, ideally, with some sort of adjusting device to trigger at the appropriate voltage. I'd just thread a piece of threaded clear tubing, or even a monster machine nut and epoxy the 'trodes into a drilled out nylon allthread holder, each, so you can screw them in and out of the nut to adjust the gap.

Barring that, just use the NGK's, and toss the stickers on your truck. They'll make it go faster.

Really.

iEdd
12-28-2008, 03:48 PM
Looks like I will have to buy NGK then. (Easier and maybe cheaper than going out and buying a length of nylon, plus whatever fittings I need, when I could just spark plugs which have a better, ceramic insulator, which is less likely to fail.)

I was going to have 2 spark gaps in series on each side of the circuit (see OP's schematic), for 4 total as I was told this would increase the frequency further and hence reduce danger of the device.

OrionBlade2003
12-28-2008, 11:22 PM
Can you email the schematic?

I might could redesign it for you so you only need one.

What frequency do you need to run at. Kilohertz I assume?

I can make a 10ns pulse with some coax and a spark gap at 100KV on a 100 ohm load.

That's retarded current (at low duty cycle). You might even do an argon spark gap.

I can even post a design for you for a kick@$$ simple spark gap setup so you don't have to jerry rig anything.

*rummages through the thread*

Rion.Motley at gmail.com btw.

OrionBlade2003
12-28-2008, 11:39 PM
You're talking about the copper block in the upper right hand part of the enclosure?

http://www3.telus.net/public/a5a26316/Newgraphics/ArcStart2.jpg

No way is a spark plug going to last longer than 30 or 45 seconds if you're switching the output of the transformer (which it looks like from the size of those heat sinks). If this is on the input side, then that's fine. I would never ever ever run two spark gaps in parallel, and there's absolutely no reason to run them in series unless you need to do some sort of voltage dividing between them.

Email me and catch me up a bit, and I'll be happy to chat - Just read through 90% of the posts, and downloaded the PDF way back, as well as checked the telus site.

Anyhow, have a nice night,
Rion

integerspin
12-28-2008, 11:48 PM
Think someone wanted to see the schematic for a tig.
My murex schematic is online, put it there when i asked some questions about fixing it, amazingly I managed to fix it;-)
the schematic shoudl be HERE ("http://integerspin.co.uk/downloads/transtig.pdf)
The spark gap is a plug with the electrode sawn off. I have owned it 20 years and it came that way. I didn't really understand the hf part of the circuit, it looks very like pics of marconi spark transmitters!

iEdd
12-29-2008, 12:41 AM
What frequency do you need to run at. Kilohertz I assume?

Low MHz preferably. I think they can be from about 100kHz to 10MHz...

brainstatic
12-29-2008, 02:44 PM
Not all NGK spark plugs intended for "street" autos are non-resistor type. My Jaguar V12 uses an NGK resistor plug. I would think best to contact NGK before purchasing.

From their website:
Technical Support
hours: 8:30am - 5:00pm Monday-Friday EST
tel: 1-877-473-6767 prompt #2

http://www.ngksparkplugs.com/About_nGK/contactus.asp

graflex
12-29-2008, 03:21 PM
The HF non touch arc striker/maintainer cct is essentially a TESLA COIL. This is a high frequency tuned step up transformer. The 2000-3000 volts from the neon sign xformer and capacitor is 'chopped up' by the spark gap and generates a hf supply to the primary of the step up transformer. The spark gap is crucial in giving the right frequency and shape to the pulses. A auto spark plug will not last very long before the gap burns away and the characteristics of the circuit change. A pair of 1/4" dia. tungsten buttons mounted on heat sinks are invariably found in most commercial units. Best of luck.

iEdd
12-29-2008, 04:37 PM
Not all NGK spark plugs intended for "street" autos are non-resistor type.

Mine are. ;)

The place I bought them (Supercheap Auto) here in Australia had an NGK catalogue with the first page having 2 columns "non resistor" and "resistor". I had about 100 part numbers to choose from.

If the spark plugs fail, after everyone saying how well they work - and how long they last in an engine, which is much hotter than this, then I'll buy the largest tungsten I can find and use the heatsink method. :)

OrionBlade2003
01-02-2009, 02:36 AM
Think someone wanted to see the schematic for a tig.
My murex schematic is online, put it there when i asked some questions about fixing it, amazingly I managed to fix it;-)
the schematic shoudl be HERE ("http://integerspin.co.uk/downloads/transtig.pdf)
The spark gap is a plug with the electrode sawn off. I have owned it 20 years and it came that way. I didn't really understand the hf part of the circuit, it looks very like pics of marconi spark transmitters!


Dude, could you take a photo of that spark gap?

My experience with pulsed power has been hundreds of thousands of volts at hundreds of thousands of amps for hundredths of thousandths of thousandths of seconds.

umm... P=VI, so 100,000V at 1000 A = 1MW.

For 10^-7 seconds, that's .1 joules per pulse.

Spark plugs work great at those energies, but the electrodes start melting when you start cranking the duty cycle up, and we move to brass and tungsten with a pressurized inert gas of one species or another.

I've also done triggered spark gaps, so that might be helpful here. Anyhow, a photo would be totally bad@$$.

:cheers:

OrionBlade2003
01-02-2009, 02:39 AM
Not all NGK spark plugs intended for "street" autos are non-resistor type. My Jaguar V12 uses an NGK resistor plug. I would think best to contact NGK before purchasing.

From their website:
Technical Support
hours: 8:30am - 5:00pm Monday-Friday EST
tel: 1-877-473-6767 prompt #2

http://www.ngksparkplugs.com/About_nGK/contactus.asp

Dats wha we use dem dere race plugs. Makes dem 'lectrawns go faster.

:banana:

iEdd
01-02-2009, 03:22 AM
Anyone looking for the non-resistor type, get an NGK B7ES or B4ES (and many more), but they are the ones I remember are definitely not resistor type.

Just tested with a multimeter. The Champion Gold (resistor plug) have 94kΩ of resistance through the inner electrode. The NGK (non resistor) have about 5kΩ - I'm slightly surprised that this wasn't a lot closer to zero. I guess it is because the nickel-alloy electrode is not that great a conductor.

integerspin
01-02-2009, 12:49 PM
I will have to move some stuff to get at the side of the tig to take a photo. The spark gap is a spark plug,as I said before, and L2 in the diagram looks like a car coil, L1 is an aircored inductor wound from thick section aluminium and will probably be visible in the photo. If I can get the top off the tig I will check the coil part number, it looks like a normal car coil and the capcitor values..

OK. Spark plug is a Bosch W8DC [M5 bmw?] picture[CLICK ME (http://integerspin.co.uk/ebay-images/spark-gap01.jpg)] picture is not brilliant but you can see how the electrode has been chopped off and the errosion of the electrode. It's been in use at least 20 years.

There is a picture of it place CLICK ME (http://integerspin.co.uk/ebay-images/spark-gap02.jpg)
Caps[C3] are 2 off 100uF 100V.

inductor 1 is HERE (http://integerspin.co.uk/ebay-images/spark-gap03.jpg)

coil isn't very exciting, it has HOGEFFECTSPOLE art 1120 12v written on it.

OrionBlade2003
01-02-2009, 02:44 PM
er... integerspin...

Awesome. The electrode would have eroded away long ago had it not been ground off to begin with. I wonder if you cleaned the plug up, would it still work?! Looks like a nice sputtered coating of metal all around there, approximating an isopotential surface :-p

Anyhow, that helps a bunch. We used the plugs as-is, since our duty cycle was so low - a few dozen hertz at most, with nitrogen or argon flowing through the unit at elevated pressure, cooling it and altering the breakdown characteristics.

Anyhow, thanks again - very enlightening. I love old equipment - I've got a 1939 buick sitting in my garage that needed less work to get running and maintain than any other modern car I've had.

iEdd
01-25-2009, 07:33 PM
js530, and anyone else that has made this:

How is your capacitor arrangement at arresting HV/HF and stopping it from killing the diodes? I got X2 mains suppression caps which are twice the microfarads of yours. Just want to know if there are any blown diodes or welder damage. Asking because other circuits I've seen have a 5k ohm resistor (10W or so) in parallel with the capacitor(s) which yours doesn't have and wondering if this affects it?

slappynuts
02-17-2009, 10:01 PM
Wheres the thread on your DIY Plasma Cutter? :)

Exactly my thoughts.

You guys do realize that this could be done with junk from any junkyard and a few parts from the hardware store right? All these transformers and capacitors may have been the latest rage in the 40s when this circuit was designed but it is obsolete at this point in time.

Basically you can build your high frequency parts with a car coil and ignition module from the junkyard and a light dimmer sitch from the hardware store.

slappynuts
02-17-2009, 10:13 PM
Here is the answer to all of your questions.

http://www.geocities.com/CapeCanaveral/Lab/5322/simpleign.htm

iEdd
02-17-2009, 10:15 PM
Basically you can build your high frequency parts with a car coil and ignition module from the junkyard and a light dimmer sitch from the hardware store.

Yep. (http://www.casano.com/projects/hfstart/index.html) (Warning: This one is for an AC Stick welder. For DC stick or TIG you will need the usual suppression circuitry across the -ve and +ve rails before the HF stuff.)

Too bad that gem of an article wasn't written until after I spent $120 on a Switchmode NST that doesn't work in this application.

slappynuts
02-17-2009, 10:39 PM
Yep. (http://www.casano.com/projects/hfstart/index.html) (Warning: This one is for an AC Stick welder. For DC stick or TIG you will need the usual suppression circuitry across the -ve and +ve rails before the HF stuff.)

Too bad that gem of an article wasn't written until after I spent $120 on a Switchmode NST that doesn't work in this application.

Well isnt this part just a spark plug(gap) and wrap some wire from the spark plug ground around your tig torch lead? The one in the now missing DIY plasma cutter page used a GM coil and GM ignition module or something like that. Im looking for a better diagram ATM.

slappynuts
02-25-2009, 08:16 PM
Ok I just tested this set up as working. This is as cheap and simple as it gets (and reliable).

http://i279.photobucket.com/albums/kk128/jimmyj900/Steam%20And%20Mad%20Science/Jacobs_Ladder_Gill_Coil.jpg

I plan on using a spark plug for my spark gap (im thinking lawnmower plug and a solid core plug wire). To finish off the high frequency part i think a length of pallet banding thats anealed and wrapped in a loop with a few windings around each side.

I used a 4uf 660v oil filled cap I found at the local junk surplus store for $4 , chinese knockoff bosch coil from fleet farm for $11.79 and a cheapo dimmer switch from fleet farm as well $2.79 .

My next stop will be to harbor freight tool to get the cheapest stick welder they have and grab a tig torch from work and a regulator(more to come).

scirturbo
04-26-2009, 09:32 AM
Punisher, any update of your project?

punisher454
04-26-2009, 05:02 PM
Punisher, any update of your project?

Sorry, no progress yet, I have 2 projects in the works that have to take priority right now. A couple times a week I do look over at the arc welder, tig torch and box of electronic components sitting on top and wish I had time to put it together.
The thing I'm working on now should be finished by mid summer and then I'll be able to get on to the tig welder.

I am intrigued by the dimmer idea for the HF.

nutchanon
05-26-2009, 02:56 PM
this schematic can make tig welder

mecanno
07-07-2009, 12:52 PM
i have built an similar arc starter but destroy my rectifer diode i need help for finish sorry for my english y am french boy i dont have filter capacitor

Stanislaw Krasi
10-15-2009, 08:03 AM
Look here: http://www.elektroda.pl/rtvforum/topic128923.html
Stanislaw Krasicki
Szczecin
Poland

ozzie34231
10-19-2009, 11:15 AM
Hi All,
I see this thread has gone a bit dead except for a Polish post that I can't read. I posted here a while back asking what is needed to do TIG with an AC buzz welder. Though some have added to the thread, and some quoted my question, I'm still a bit in the dark.
I've looked at the High frequency start box, and the Jacobs ladder, and while that might be clear to most, I'm still a bit in the dark.
I can build either of those or the thing posted by Nutchenon, but then what? Do I put those outputs in series with my electrode wire? That's putting a #8 wire in series with a very heavy welding cable??
Then I'm all confused about spark gap. The starter box has three gaps, while others talk about using a single spark plug???
Assuming I can get to the point of understanding the construction, what kind of TIG welding will it enable? Steel? 1/8" 6061? What would be the suitable applications?
I notice the "starter box" appears to have a foot switch. Does one only start the TIG arc with the High frequency, or is it fed constantly?

Thanks, maybe someone can alleviate part of my stupidity,
Ozzie

Stanislaw Krasi
10-19-2009, 01:00 PM
TIG AC/DC 400A Home Made in Poland
Stanislaw Krasicki

iEdd
10-19-2009, 04:17 PM
Hi All,
I see this thread has gone a bit dead except for a Polish post that I can't read. I posted here a while back asking what is needed to do TIG with an AC buzz welder. Though some have added to the thread, and some quoted my question, I'm still a bit in the dark.
I've looked at the High frequency start box, and the Jacobs ladder, and while that might be clear to most, I'm still a bit in the dark.
I can build either of those or the thing posted by Nutchenon, but then what? Do I put those outputs in series with my electrode wire? That's putting a #8 wire in series with a very heavy welding cable??
Then I'm all confused about spark gap. The starter box has three gaps, while others talk about using a single spark plug???
Assuming I can get to the point of understanding the construction, what kind of TIG welding will it enable? Steel? 1/8" 6061? What would be the suitable applications?
I notice the "starter box" appears to have a foot switch. Does one only start the TIG arc with the High frequency, or is it fed constantly?

Thanks, maybe someone can alleviate part of my stupidity,
Ozzie

1. Try running the Polish site through Google Translator (translate.google.com), there looks to be some interesting stuff there.

2. Yes it's run through in series, but remember that the shorter the wire, the less resistance, so it's OK to use a smaller wire (though mine uses 25mm^2 welding cable, which is about the biggest a hobby machine ever uses for its electrodes). WELDER->HF UNIT->TORCH & WELDER->HF UNIT->CLAMP

EDIT: Bear in mind the schematic at the top of this page is for an AC welder only. (It only runs the torch through the system.) For DC, you need both the earth clamp and torch run into the unit so that you can have capacitors to arrest the HV. Otherwise you will destroy your diodes.

3. More spark gaps will increase the voltage drop (series), or reduce the wear (parallel).

4. Hard to know what the limits are. I suppose whatever the weakest component can handle.

5. The HF needs to be on continuously for AC welding, as the arc is broken twice a cycle, but for DC, you only need to initiate it once, then turn the HF unit off.

Someone who understands it better can probably help you further...

djowen41
10-20-2009, 02:19 AM
Hi guy i have read this entire thread and i'm very interested.

Does any one no of a reason that the ignition coil based HF starter wouldn't work with an inverter welder?

Cheers

iEdd
10-20-2009, 02:25 AM
I hope not! That's what I'm in the process of doing. Just make doubly sure that you're arresting the HF/HV from entering the welder.

Stanislaw Krasi
10-21-2009, 12:32 PM
Probka spawania Al spawarka w wykonaniu domowym (grubosc: 4 mm). Gaz: Ar (99,999%) "5,0"
Pozdrawiam
Stanislaw Krasicki

Stanislaw Krasi
10-21-2009, 01:08 PM
ROV, made by domesic welding machine vehicle.

Stanislaw Krasi
10-21-2009, 01:11 PM
ROV made by domestic welding machine vehicle
Stanislaw Krasicki

ozzie34231
10-22-2009, 12:22 PM
Thanks iEdd,
That clears some of the fog.
Ozzie

Hawkins
12-05-2009, 10:28 PM
Hello,
Im new to CNC Zone. First of all I would like to thank all of you guys for keeping this thread alive so long:-). I have recently aquired via the evilbay some massive torroids. They were from a big TIG welder and are 3.4KVa each.
I have done a lot of research since then and hope I can help.
First lets hit on this HF start thing and then work back. If you look at:

http://www3.telus.net/public/a5a26316/TIG_Welder.html

You will see that he uses a distributed gap (gaps in series). This allows a lower dissipation in each gap. This is good because it means that each gap will heat up less. Also it allows fine tuning of the total gap. He has labeled his as 8 thou (mills) gap, I guess this is total, so 2 thou each. More information on this set up is easy to find on Tesla coil sites. I really do wonder if one spark plug will last long in this sort of service. I am going to use some 4mm OD tungsten. I got it from the usual place, 1 quid for a 100mm length, I bought two lengths, I will cut it up with a dinky diamond disk. I will mount this in some half inch square brass bar I have using little 3mm grub screws to allow adjustment. Tungsten can be brazed for those with the inclination, this would mean having access to a surface grinder with a green wheel to set them all level, too much messing about for me. Now we know the sort of heatsinking and precision needed for reliable operation over the long term. This is imperitive, I had whack from an old school tig set up that knocked me out. The fact my mate thought it would be funny to zap the back of my neck with it was not the real reason(OK yeh it was, dead leg issued). I was not too pleased as you can imagine. The gap had eroded, ablated, whatever. It was giving out 5-10Kv at one or two pulses a second with a pretty high current. OUCH. Stick the filler to the job, try and use the torch hand to get it off and wollop. Yeh not good.

As for getting a TIG welder from your old stick gear. I think its cracking idea. I have not seen much recent use for full on sine wave AC. So a rectifier will be needed. The really old 50-60Hz ac set ups dont cut the mustard. You will go through electrodes like they grow on trees. So rectifier it is then. But which? There are some choices. Normal bridge type rectifier. Pros- easy, relatively cheap. Cons- no current control. This should not be a problem if you already have current control on you stickamajig. SCR controlled rectification. Well this is the one really for a DC set up. Fully controllable, some use an auxilliary supply to give really low arc currents. This is how they weld razor blades, ally foil etc. (they dont but it is possible, LASER is the way for this sort of thing).

The one trouble with any sort of semiconductor output stage is adding the HF start. The HV will puncture the diode/IGBT/MOSFET/SCR junctions easily. The thing is its HF, normally >500KHz or so. This makes it reasonably easy to bypass to ground (a relative term, the earth clamp) some film caps will do the trick. Most also use tranzorb type avalanche diodes. If anyone knows more about ratings type numbers etc I would be very pleased to hear about them? Also another good reason to ensure you have the best spark gap possible, as any wear over time will lower the frequency and destroy your expensive semis.

Anyway, this is the stuff I have worked out so far. Here are some Patents that make interesting reading if you can get over the usual " cover it all and sue" style of most US patents.

US6388232 - interesting
US5229930
EP 1 782 907 A2 - this a Euro one.


Cheers Matt.

siciunas
01-19-2010, 07:40 PM
This thread is pretty old, but I felt I had to thank the contributors for setting me straight. I have just built an HF arc starter using spark plugs. It had a nice spark at the gap, but no arc at the output. Then I saw the warning about about resistor spark plugs and DUH!!!! the light bulb came on! I had used resistor plugs! I switched them to gaps using coat hanger wire to try it, and it worked great! Thanks to this forum! Now I'll tweak it a bit to optimize performance. The basic circuit I used is Chris McKinnon's. I can post pictures or schematic if anyone's interested.... Thanks again...

Eugene

iEdd
01-20-2010, 03:01 AM
Thanks for that, I was thinking of bumping this topic anyway. Please post your schematic from Chris McKinnon.
Any updates from anyone? Punisher, et al?

Anyway, regarding the spark plugs - I noticed before that my "non-resistor" plugs were still reading as 5k ohms, so after reading your post, I wonder if this is why I couldn't get it working.

There are 2 arrangements I've seen people use for this project, and they are similar to the diagrams here (http://en.wikipedia.org/wiki/Tesla_coil#Utilization_and_production) about Tesla coils. Notice the spark gaps in parallel with the HV output is preferred to protect the transformer.

Anyway, when I was working on this (nearly a year ago), when I connected it up that way (diagram 1), I got no sparking on the gaps (though I did get maybe 0.25mm arc from the torch to the earth clamp). I believe it's because I have a 20kHz switchmode NST and the path of least resistance was through the capacitors/coil, not the spark plugs (4 at 0.5mm and 5k ohms of resistance each), so it was essentially shorting the gaps. I'll try as you say, with coathanger wire, and see if it works.

My other theory is that a higher frequency supply (20kHz vs 50/60Hz), would need lower capacitance for the same reactance, so instead of maybe 1500-2500pF, something like 5pF should be used to give the same reactance. There's also the coupling transformer though, which increases reactance as frequency increases, so it's possible that the number of turns would need changing too.

Has anyone had any luck with using switchmode supplies at these higher frequencies? Or any comments from someone with a really good understanding of AC theory?

I've already bought all the stuff to make this with the dimmer/cap/ignition coil, but it would be nice to get it working with the NST.

siciunas
01-20-2010, 12:34 PM
Hi iEdd:

I've attached the schematic and text description of the McKinnon Arc Starter. The spark gaps can be in series and don't have to be on opposite sides of the coupling coil. Same for the 5 ohm resistors. When I get a chance I'll try to make a photo of my setup.

After I saw the note about resistor plugs I went to the garage and dug out my spare lawnmower plugs - Champion CJ6, definitely NOT resistor, but I decided to measure them anyway. One was zero ohms to the electrode, the other was open! And these are brand new, never used plugs. I tried using just the good one, got a nice spark at the plug, but no arc. This did not surprise me since I had read somewhere (on a Tesla site I think) that you need several gaps in series to facilitate quenching the spark as the input voltage drops. Then I switched to coat hanger wire, which worked fine and I can replace with Tungsten TIG electrodes if the wire burns away too quickly.

Your Tesla site says that the HiV transformer needs to be able to survive high frequency voltages. The McKinnon circuit incorporates a low pass filter to protect the transformer - nice!

My understanding of how the spark gap generates High Freq is that the HiV transformer charges up a capacitor which is then shorted through a tuned circuit, formed by the capacitor and the primary of the coupling transformer,
by the spark gap firing. This happens 120 times a second for a 60Hz transformer. The ringing frequency is determined by the reactances of the capacitor and the inductance of the primary winding. If you use a 20Khz source, then the repetition rate is merely higher. The frequency is still determined by the tuned circuit.

My next step is to set the coat hanger wire gaps to 8 thou each and vary the number of turns on the coupling transformer. It's now 14:14. I think I'll try 8 0r 10:14 to try to raise the output a bit. I put some ferrite rods into the winding core to improve the coupling, but I'm nervous about using too much to avoid coupling any 60Hz, dangerous, voltages....

Thanks for your interest....

Eugene

iEdd
01-20-2010, 03:56 PM
Thanks for posting that. Hmm, okay, so if the resonance is determined by the caps and the coil, then the frequency of the HV supply doesn't matter?

As it's been nearly a year, and I'm trying to relearn all the stuff I researched so I can get this finished. The other thing I didn't understand - if the suppression network (say, 250V 0.47uF cap and resistor in parallel) is the only path for the HV/HF current after the coupling transformer, how come the capacitor doesn't have to be 15kV? I know it's fine in practice - I think mine is about 500V, but why doesn't it need to be an HV cap?

siciunas
01-20-2010, 04:23 PM
Hi iEdd:

Yes, that is my understanding. The high frequency ringing voltage is determined by the tuned circuit, not the excitation frequency (EF). Of course if the EF were close to the ringing frequency then that's another matter.

The high frequency high voltage is developed across the secondary winding of the coupling transformer. One side goes to the torch, the other to the supply, from the buzz box, which is relatively low voltage above the "Work" wire (about 70 volts open circuit). The suppression cap is to keep any high frequency high voltage away from the rectifiers in the buzz box (if any). If no rectifiers, it just protects the transformer. That's why the "Work" wire has to be brought to the HFAS, so that the high freq high voltage is suppressed right in the HF box, and can't get to the buzz box. At high frequency, that suppression cap is almost a short, so very little voltage develops across it. I don't know if this helps explain things, but that's how I see it.....

I just checked my spark gaps and they're around 10 tho. I rewound the coupling transformer to 9:14 ratio. With no ferrites, the arc is around 1/8 inch, with one rod, it grows to 3/16 " and with two ferrites, it blasts along at 1/4". Now I want to rig up a probe to my oscilloscope so that I can determine the frequency to reassure myself that it's high enough not to fry me. With all the arcing going on, the 'scope is almost useless. I need to add suppression filters to the HFAS input power lead and the 'scope supply to see if I can get a stable image.....

Regards

Eugene

Stanislaw Krasi
01-22-2010, 12:16 PM
Look hier:http://id.electroda.com/topic773495-30.html

Stanislaw Krasi
01-23-2010, 03:32 AM
Hello
Look hier:http://ca.electroda.com/topic773495-30.html
Stanislaw Krasicki

iEdd
01-23-2010, 03:47 AM
Thanks for trying to help, but the translation of that forum to English is still pretty much impossible to understand in any sort of useable detail. Can anyone make sense of it and explain it?

siciunas
01-26-2010, 07:52 PM
I too could not make much of Google's translation of the Polish forum. Pity!

I finally got around to taking some pix of my breadboarded arc starter. I've attached three. They show it from various angles, one with a nice arc. The coat hanger spark gap is clearly visible. Right now I only have two ferrite rods in the coupling coil. I'm waiting to get some more from an eBay seller. The transformer is 5000 v @ 30 mA. Its type is listed as "Fly Grid". I guess it was made to zap flies. The 500 pF doorknob across the HV terminals is part of the low pass filter keeping the RF out of the transformer. The resistor part of the filter is seen vertical. I only used three 591 pF doorknob caps for the resonant circuit. With four I thought the frequency would be too low. it arcs fine. Now I'll take it apart and build it into a proper metal shielded box. I'll use a remote foot switch to power a relay to turn the arc on, so that I can control it easily and not run it more than necessary. A noise suppression filter on the line supply is just barely visible in one of the pics. Otherwise the circuit is as described by McKinnon, which I had posted earlier.

Regards, Eugene

siciunas
01-26-2010, 07:54 PM
Hmmmm, the pix didn't get attached..... I'll try again.

Duhh! I forgot to click on the "Upload" button ! :-(

Orvillefpike
01-30-2010, 11:29 AM
Eugene,

Where did you get the doorknob capacitors?

Thanks

siciunas
01-30-2010, 11:48 AM
The white doorknobs I actually got from eBay for a few dollars each about a year ago. I see that now they are going for about $35 each!!!! I looked around the electronics surplus stores in Toronto a year ago and they were all out of them - it seems that Tesla fever had struck and they had all been gobbled up. It seems that that might still be the case, hence the high price in light of short supply. The little brown doorknob came out of some high voltage research equipment that had been disposed of in the building where I worked.

Regards, Eugene

Orvillefpike
01-30-2010, 02:40 PM
I can make a capacitor bank for about $5.00 to $10.00 with surplus capacitors, it would have bees simpler to just buy one that would do the job.
E-Bay had some doorknob capacitor, a little while ago, that where reasonably priced but the shipping rate was indecent.

Thanks

Orvillefpike
02-02-2010, 12:22 PM
Eugene,

I noticed, in Post #88, that you mentioned that you measured the resistance of a brand new spark plug and it read "open", some spark plug have a "spark gap" inside them, it could be what you have, if it's the case, it might still work.

siciunas
02-02-2010, 01:54 PM
Hi Orville: Yes, I knew that some plugs had an internal gap, but here I had two IDENTICAL, brand new Champion CJ6 plugs, presumably bought at the same time, yet one had zero ohms to the electrode, the other open. Maybe the one with zero ohms shorted out an internal gap. At any rate, I'll try them both in my lawn tractor and it'll be interesting to see what difference there is.
I'm still waiting for my eBay ferrites to finish putting the arc starter into its final box. More pictures when I'm done....

Thanks for your interest....

Eugene

Orvillefpike
02-02-2010, 02:19 PM
Now that you mention ferrite rods, something else caught my attention, you said you where worried that putting too many of these rods might transfer some of the 60 Hz to the output. At high frequency, an air core transformer is efficient enough so it doesn't need an iron core, by adding some ferrite rods, you increase it's efficiency, is it automatic that it will also transfer some of that 60 Hz signal?

Thanks

iEdd
02-02-2010, 03:45 PM
Won't the fact that you're taking the ouput voltage across an inductor be a high-pass filter anyway?

siciunas
02-02-2010, 07:17 PM
Hmmmm. I never thought of it that way. Of course, the reactance of the inductor increases with frequency, so at high(er) frequency, the reactance is much higher than for 60 Hz. So at 60Hz, much less energy should be coupled to the secondary, but then you've got thousands of volts to play with at 60 Hz. I could never get enough noise suppressed to actually see the output on my oscilloscope, so I couldn't determine the real frequency. My reasoning was that more ferrite would improve the coupling between primary and secondary, but would also increase the inductance and hence lower the resonant frequency. (That's why I removed one of the four doorknobs, reducing the total capacitance to 1773 pF from 2364 pF.) While not the same as an iron core, the more ferrite one sticks in the core, the more coupling at low frequencies there would be. But I think the high pass filter effect iEdd mentioned tends to reassure me more.

Thanks for your interest...

Eugene

siciunas
02-03-2010, 09:03 PM
Greetings! Since I couldn't measure the frequency of the resonant circuit while running, I decided to measure it passively, when it's off. I shorted out the spark gap, and recalling my Ham radio days, I could determine the resonant frequency by connecting a variable oscillator across the circuit, sweeping then frequency and watching for a peak. This is like using a grid-dip meter in reverse for the hams among us. I have a sweep oscillator and oscilloscope and I put them to use. First I swept the oscillator through its various ranges to verify that the output stayed fairly constant - it did. Then connecting it to the coil and doorknobs, I found that without the ferrites in the coil, the resonant frequency was 1.8 MHz. With one ferrite added, the amplitude went up and the frequency went down to 1.23 MHz. With the second ferrite, it dropped further to 1.16 MHz. To verify that this was behaving properly, I added back the fourth doorknob that I had previously removed and the frequency dropped to 1.0 MHz - exactly as expected. WOW!

This is great! The only thing that bothers me is the role of the spark gap. I thought it was just to excite the resonant circuit, and had no effect on the resonant frequency. However in an earlier post in this forum, I think, someone said that as the spark gap burned larger, the frequency would drop, even to the extent that the bypass capacitors protecting the rectifiers in the buzz box would become ineffective and one could blow them (the rectifiers).

In a Miller manual on one of their arc starters, I saw a note to the effect that if one of the doorknobs were to fail, one could still use the box by reducing the spark gap to 4 thou from the usual 8 thou. I don't understand this. Does anyone have any insight into this??? Why should this be the case???

Regards, Eugene

Orvillefpike
02-05-2010, 12:11 PM
Eugene,

I’m not very good with resonant circuits so I have a few questions about your tests.
Your circuit is fed by a 60 Hz transformer, so, if there where no spark gap, the secondary of the transformer, the high voltage side, would have a frequency of 60 Hz also. You are feeding it with a signal generator which will tell you the resonant frequency which is far from 60 Hz. It is my understanding that when you turn on and off a resonant circuit it will “ring” and that is what’s “creating” the high frequency. This is when the spark gap comes into play, it turns the circuit on and off abruptly, creating ringing, causing the high frequency. If you change the gap, it will change the voltage at which the “switch” turns on and off and probably has an effect on the circuit’s response.
Also, I don’t know if this would apply here but, in a car, the turn ratio, in the coil, is not what tells the circuit what the voltage of the output will be. When the points or transistor, turns the supply to the coil off abruptly, the output voltage is in relation with how fast the current in the coil drops.
Don’t take all of this to the bank though.

Thanks

siciunas
02-05-2010, 02:56 PM
Hi Orville: I understand and agree with most of what you said. The size of the spark gap will determine how much voltage is needed to fire the gap. The smaller the gap, the less voltage needed. Since 60 Hz AC is driving the tank capacitor, it presumably starts from zero voltage every half cycle. So, the amount of voltage that fires the gap would affect how much ringing at high frequency results. The larger the gap, the higher the voltage, the more ringing, the higher the voltage at the high frequency arc. I still don't see how the size of the spark gap alters the high frequency.

As to the car ignition coil - and this is where I disagree with you (a bit), it is true that the speed of the turn off determines the size of the resulting spike, but the turns ratio increases the voltage of this spike, by the turns ratio. In a conventional Kettering ignition system, the points open, the resulting arc goes out, (presumably modified by the point capacitor) and you get a spark. There is not much one can do to affect the speed of the turn off, (other than playing with the degree of saturation of the coil) so the turns ratio is set to generate a high enough voltage to fire the spark plug. With a more modern transistorized ignition system, there are more parameters you can diddle, but I still remember seeing ads for high voltage, high turns ratio coils.

Thanks for your interest, Eugene

Orvillefpike
02-05-2010, 03:28 PM
The speed of the current drop is affected by the capacitor, there is no sparks between the points, otherwise they wouldn't last very long. You can have a coil that has a 100:1 ratio and get 30 kV with a 12 Vdc supply. I think it answers to the dI/dt equation, not 100% sure though.
My question was, if you figure out that you circuit delivers maximum output at lets say 1 mHz, it might not mean that, when it's connected to the spark gap, it is operating at that particular frequency?

siciunas
02-05-2010, 04:04 PM
Yes, the capacitor exists to eliminate the spark across the points, but the coil's turns ratio is much greater than 100:1. The collapsing field in the ignition coil primary may generate hundreds of volts, but then you still need a couple of hundred to one turns ratio to get 35 or 40 KV at the spark plug.

All I can say is that the tank circuit's resonant frequency is around 1 MHz. I still don't know or understand how the size of the spark gap affects this frequency. So I still don't know what frequency it runs at when the spark gap is driving it. I even tried to measure it directly by using a small coil wrapped around one of the ferrites to input the oscilloscope, but the spark gap arcing generated so much electrical noise, I can't get a stable trace. So unless someone else can shed some light on this, it may remain a mystery.....

Regards, Eugene

Orvillefpike
02-05-2010, 04:38 PM
Have you tried a circuit simulator? I once tried that kind or circuit in LT Spice but I couldn't get the spark gap to work.

siciunas
02-05-2010, 06:03 PM
No, I don't think a circuit simulator would be of much help because I can't think of an electronic device that would faithfully simulate a spark gap. An avalanche diode might fake the triggering at some high voltage, but not the shut down as the voltage drops (except for zero). I'm hoping someone reading this exchange may have some insight (experience) into what's really going on here.

Thanks for your continuing interest. Eugene

Orvillefpike
02-05-2010, 06:34 PM
Someone, in Yahoo's LT Spice forum, told me how to simulate the spark gap but I got discouraged and didn't get it to work. Then again, there might be no accurate way to simulate something like that.There is a bunch of brilliant people on this forum though.

siciunas
02-05-2010, 07:51 PM
Well I hope one of these brilliant people on this forum can enlighten us, but it's been pretty quiet for some time..... Hope springs eternal...

Thanks again for your interest and comments.

Regards, Eugene

Orvillefpike
02-05-2010, 11:37 PM
There are a bunch of forums, on Yahoo, where you might find answers, there is Electronic_101, Welding_Project, usa-tesla. Why do you want to know what frequency it's operating at? Or do you just want to know the effect of the spark gap on the circuit?

siciunas
02-06-2010, 01:47 PM
I am a retired EE, so I have an innate desire to understand how things work. I'm also concerned that the arc starter frequency be high enough to exhibit the skin effect, and hence not fry me when I use it with a Tig welder. Hence my earlier concern about coupling 60Hz energy to the coupling coil.

I did a Google search on spark gaps and found a whole bunch of info, mostly from the Tesla Coil bunch. Everything I have seen says that the frequency is determined by the resonance of the tuned circuit, NOT the spark gap size. Here's a neat simulated analysis:

http://www.richieburnett.co.uk/static.html

The spark gap does affect the amount of energy coupled to the coupling coil. The larger the gap, the higher the voltage needed to fire it, the more energy transferred to the tank circuit. This may be desirable for the Tesla folks, but my arc is plenty strong already. A smaller gap will fire at lower voltages, so the charge capacitor can charge up more quickly between firings, and you can get more firings per half cycle of 60 Hz input. I don't think this is a big deal for Tig welding, since one firing is all that's need per half cycle, and the ringing gives multiple arcs.

So I think the frequency I'm getting is fine, and I can put this issue to rest.

Thanks, Orville for all your comments and suggestions...

Regards, Eugene

Orvillefpike
02-06-2010, 05:32 PM
I guess the bigger the gap the more stress on the tank capacitor.

iEdd
02-06-2010, 06:36 PM
Some good info and discussion there.


[...]to exhibit the skin effect[...]

Be careful about this. The so called "skin effect" in humans is a myth. The term comes from the fact that when AC flows through a conductor with close to uniform resistance (eg, a powerline), it tends to flow more on the outside of the conductor than on the inside. The higher the frequencies, the greater the effect.

However, in humans, your skin has a massive resistance compared to your blood and soft tissue. If you perform the calculations, human flesh has a conducting "skin" of 60 inches at tesla coil frequencies - much bigger than a whole human cross-section, let alone your skin.

So the tingle you feel is much fewer ions crossing membranes before the current changes direction, so you perceive it to be less painful and less damaging.

The Wikipedia article (http://en.wikipedia.org/wiki/Tesla_coil#The_.27skin_effect.27_and_high_frequency_electrical_safety) has a heap of external references to support this, which makes sense from a logical standpoint as well, as your skin is orders of magnitude higher in resistance than your inner flesh.

siciunas
02-06-2010, 08:55 PM
Thanks for the info. Since the commercial arc starters run at around MHz, it can't be too dangerous, or they'd have been sued out of existence by now. I'll just have to remember to wear gloves on BOTH hands while welding when using the arc starter.

Regards, Eugene

Orvillefpike
02-07-2010, 10:41 AM
I have seen a guy show me how the arc starter worked, with an Econotig by Miller, by creating an arc between the torch and his hand.

siciunas
02-07-2010, 12:31 PM
Hmmmm. Well that shows that the voltage won't fry him, but the arc sure will burn though. He must have been verrry fast!!!

Orvillefpike
02-07-2010, 03:58 PM
He held the torch over his hand while he was talking to me, he did that for 10 or 15 seconds, he said it tingled.
I have a plasma globe and, I guess it's the same phenomenon, if you stick your finger close enough there's a spark between the globe and your finger and it's not painful at all

iEdd
02-07-2010, 04:39 PM
It's because your body is full of conductive ions, which move to conduct electricity. At high frequencies, they travel a smaller distance before changing direction. If they aren't crossing various membranes, the pain will be greatly reduced. I have heard stories of people not feeling much at the time with HF, but having muscle aches and pains days later.

I think the point to take away from this, is it's still HV and you should try to keep out of the circuit.

Edit: Here's an example of a calculation of skin depth at 1MHz in a human:
http://www.sgoc.de/Download/skin_effect.pdf

Orvillefpike
02-07-2010, 07:09 PM
Something else that crossed my mind, in the link you provided, about spark gaps, the capacitor they use is much smaller than the one you use in your circuit.

siciunas
02-08-2010, 09:58 AM
If you're referring to the 64 nF capacitor mentioned under one of the graphs in that spark gap link, it's actually much bigger than what I use. My tank capacitor is 1773 pF, or 1.773 nF. The spark gap link is oriented towards Tesla Coils, and I think they use much bigger capacitors to transfer more energy into the Tesla Coil. The more energy, the bigger the display!!

Orvillefpike
02-08-2010, 10:04 AM
Oups, I didn't pay attention, again.....

dr pepper
03-01-2010, 09:10 AM
Hi Chaps, I'm going to revive this thread a little.

Further up there is a reference to a site that describes a 'hf start box' and uses a car ignition coil.
This is a great project, only when I printed the thing out and looked at the layout of the box, the wiring looks diffo to the scheamtic, and the schematic seems incorrect, shouldnt the cap and resistor be accross the ign coil windings?.

The reason why I'm interested in the auto ign coil version is that I want to make an on board weld set for my 4x4, one that does mig, tig and stick, the works, and I need a 12v to several kv source, so the ign coil is perfect and cheap, there are several circuits on the net for generating high tension from car ign coils from 12vdc, so I'd use one of those to drive the coil.
Could I use spark plugs instead of spark gaps (yep I know ngk non resistive ones), and I presume I still need 3 for spark quenching.

siciunas
03-01-2010, 11:43 AM
Which schematic are you referring to?? I saw one where the coil is driven from 117 VAC through a series capacitor and a lamp dimmer to provide the interruption, but you want to run it from 12 vdc. So, you'll need something to generate a string of pulses to excite the coil to create the high voltage to arc through a spark gap that will resonate at a higher frequency.

In my case, two spark gaps were sufficient to create the high voltage and still quench themselves, though I gave up on using spark plugs, in favour of coat hanger wire. They still haven't melted enough for me to worry about....

Regards

dr pepper
03-01-2010, 12:38 PM
Yep thats right its the one with the old automotive ign coil and the lamp dimmer, the output coupling xformer is a tv line output yoke.
The schematic looks diffo to the layout in the photo's, I was gonna put the photo's up here but realised that I dont have the rights for that, heres a link to the article tho to save you chaps from routing:-

http://www.casano.com/projects/hfstart/index.html

I have a little circuit in mind that uses a 555ic and a darlington to drive the coil from 12v, I dont think the resonant freq will change though, the inductance of the primary coil and the capacitance of the parallel cap set the resonant freq as they are a tuned circuit, altering the freqiency that the coil fires at will alter the pulse rate rather than the base oscillation frequency.
I like the idea of spark plugs, they are made to withstand the application and will run for long periods without attention, well at least I'dve thought so, are you saying coathangers are a better solution?, I wondered about using the plain ends of 3mm or so hard drill bits.
2 spark gaps are the way forward then, of whichever kind.

Thanks for the reply, hows the weather is canada.

siciunas
03-01-2010, 01:46 PM
Yes, that's the schematic I recognize. Now that you mention it, it is a bit different from most of the HFAS schematics I've seen. Usually, the spark gap is either in series between the capacitor and coupling transformer primary, or across the capacitor and primary in series.

See http://en.wikipedia.org/wiki/Tesla_coil#Utilization_and_production

The layout shown in the pix does look different than the schematic. The spark gap seem to be in series with the primary of the coupling coil, the capacitor and the 100 ohm resistor. The capacitor then gets charged through both resistors, which appear across the ignition coil secondary. A little strange, but should work. He also seems to have added a foot switch to control the HFAS.

The schematic I used is in Post #88, though I had the spark gaps and resistors all in series in the same path to the coupling transformer. You can see the layout and spark gaps in post #95. the spark gap holders are merely screw top terminal binding posts, with coat hanger wire as the electrodes. I was planning to replace the wires with tungsten Tig electrodes if the wires melted too quickly, but that hasn't happened yet. I suppose hardened drill bits would work OK too.

Your use of a 555 timer chip and Darlington should work fine. You may have to play with the pulse length to avoid excessive saturation of the ignition coil, yet have a sufficient repetition rate to fire an arc to keep up with your welding source frequency. Since you're using this on a 4X4, I presume you'll be using an alternator as the source?? If DC, repetition rate won't be a problem for long as you only need the HFAS to start.

Sounds like an interesting project. Good luck.

Oh yes, the weather here in Toronto is rather balmy today - around zero Celsius, not quite like the tropical weather at the Vancouver Olympic site.

Regards

dr pepper
03-01-2010, 02:45 PM
well thats interesting, looking at other drawings and the one you reffered to I think I'll do things diffo than the hf start box I have been looking at.
A car ign coil I presume can withstand the high frequency ht as a few folks have made these without the filter without bad affects, so I'll try skipping the filter, however the 2 spark gaps and the cap/res accross the coil seems like a better config, so I'll try that with the cars coil, if it fry's I'll get another coil and build the rf filter.
I did a little looking on the web and found this little circuit for keeping cats of your potatoes, not the sort of use I'd put it too, but it'd make a good ht supply I think, the pot controls the pulse width of the output, and hence the charge time of the coil, so theres an adjustment of hf start power, even better.

http://www3.telus.net/chemelec/Projects/Car-Coil/Car-Coil-1.png

I think I'll fab a high voltage cap out of a load of 400v ones in series, there seems to be a shortage of ht caps.
Yes my source is going to be a fat alternator of about 200a, I have drawn a little circuit that will give me a constant voltage or constant current, with outputs for the gas valve and auto control of the hf, I plan to use a spool gun for mig.

The weathers cold and dark here too, but not as bad its about 8 degrees c and its been a nice day, I'm here at work till 22:00 so it'll be dark by then.

iEdd
03-01-2010, 06:14 PM
Side note: If you want to drive the coil with DC, you will need a PWM driver, with a couple of layers of protection, such as MOVs, TVS, Caps, resistors, Zener diodes. Have a look at these 2 links for ideas:
Homemade Ignition Coil Driver (http://www.rmcybernetics.com/projects/DIY_Devices/homemade_ignition_coil_driver.htm)
Homemade Pulse Controller (http://www.rmcybernetics.com/projects/DIY_Devices/homemade_pulse_controller.htm)
(You'd want to make the one in the 2nd link, as I did, but read the comments carefully for tips on how to stop the ignition coil 'kick' from destroying your MOSFET/comparator.)

-----------------------------------------

I've just finished my HF start box, using an ignition coil.

The main components I used were (prices rounded up in Australian dollars):
Farnell:
5k, 15W Resistor ~ $5
10A EMI Filter IEC Socket ~ $10
3uF, 450V Ducati Motor Capacitor ~ $10
(I put a 10M bleeder resistor across this)

Ebay:
Lucas Ignition Coil ~ $30

Hardware Store (Bunnings):
400W Light Dimmer ~ $20

Jaycar:
6 x 0.01uF 3kV Ceramic caps ~ $12
3 x 180mm ferrite rods ~ $9

Dick Smith Electronics:
(Before they became crap and stopped selling components)
10 x 0.1uF 250V X2 caps ~ $10

There's also about $50 worth of 25mm^2 welding cable, and probably another $20 for the welding fittings (2 panel dinse sockets on the front of the box and 2 plugs out the back).

The mains side has 240VAC into the EMI filter, which goes in series with the motor capacitor, dimmer and ignition coil primary.

The circuit I used is like the one on the Miller website, or the generally preferred Tesla circuit. So the secondary side of the ignition coil has spark gaps straight across it (were spark plugs, now 3.2mm tungsten electrodes to save space). In parallel with the spark gaps are the primary coil and 18kV/1667pF capacitor bank in series.

The suppression network (to stop HV going back into the welder), consists of 5 parallel sets of 2 0.1uF X2 caps in series, giving a 500V, 0.25uF bank. This has the 5k/15W resistor across it.

------------------------------------

Pictures:
1. Comparison of new small spark gaps (3), to the old 4 spark plug setup. The space saving is huge, not to mention the extra life of tungsten.

2. Primary coil - consisting of 3 Ferrite cores inside some flexible conduit with about 12-13 turns of magnet wire.

3. Overall View. Almost everything is attached with crimp connectors with round lugs or spades, for easy modification. The blue plastic container above the ignition coil has the capacitor bank in it.

4. Front panel view. Annoyingly, this aluminium junction box had a hole drilled in it, but it was free and otherwise going to be thrown away. The dinse sockets have been mounted on a lid from an ABS project case for insulation. (I've also since put a plate over the hole with a HV warning label.)

5. 25mm^2 dinse plugs to connect to welder.

6. Closeup of EMI filter.

This will have its mains plug connected to another box (work in progress), with a relay control circuit and gas solenoid, so that I can use a 12V switch on the torch to turn this on and off safely.

dr pepper
03-02-2010, 08:41 AM
Cool thanks for sharing that, I like your machine.
I'm not too bothered about the space, and actually I like your plan with the 'plugs in a bit of drilled and tapped steel.
What was the gap on the plugs?.
I was thinking for a ferrite core I'd use a load of those of those doughnut shape suppressors end to end, nice and easy, and like you a load of caps in series and parallel to get the required voltage and capacitance.
I have some electronics test gear so I'll tune the coil and cap at low voltage first using a sig gen 300khz seems to be a popular freq, thats one benefit of using a load of caps you can re-config to get the correct value without getting more.
The coil driver I refered to actually does pwm, the pot is for the charge time or pulse width, thanks for the links though, I was wondering what to do about suppression especially when the circuit I found used a mosfet.

siciunas
03-02-2010, 10:40 AM
Very nice iEdd!!!!! Thanks for the links about using ignition coils. Even though I'm quite happy with my "Fly grid" transformer-based unit (for now), it never hurts to have more info available. I take it you gave up on the NST-powered version?

Dr pepper, you seem to be well on your way to building a successful unit. I thought that the usual frequency for HFAS was about a Megahertz, but 300 KHz should do as well. iEdd makes a good point about protecting the welding source from the HF. The schematic didn't show any supressors, and you wouldn't want to fry your alternator diodes! Pls include some pix when you're done.

Regards

dr pepper
03-02-2010, 11:36 AM
Yep I think I have got a good idea on my design now.
Regards rf suppression, commercial sets and home built stuff from what I've seen just have a cap accross the output of the welder supply to short the rf back into the work, I might improve on that a little by bypasing the larger 4u7 cap with a 0.1uf and a transzorb a little higher than the max output voltage all accross the output.

Seems that altys of a larger size tend to use avalanche diodes as part of the bridge, these will fry in a dead short situation, so I was thinking of fabbing a bridge out of 4 No. 50 amp paralled full wave bridge modules to give the 200a, snubbed with the network aforementioned.

The other thing I've been thinking of is mig welding at dc needs an output choke or stabiliser on the output, the same with dc stick welding, I have a modded microwave transformer which is now a choke and works well on battery welding, however I'd like to incorporate the choke into the hf coupling transformer to save space and complication, and just not use the hf for mig but the inductance will act as my stabiliser, the issue is with ferrite is saturation of the core, ok for a hf start coil as the heavy current wont be flowing during the start phase, so I guess I'd have to build an air cored coupling coil, its gonna be large with a 1mh inductance.
Fly grid hf start, now thats an idea, you can get those to run from a car battery.

siciunas
03-02-2010, 01:03 PM
You sound like you're on a good track with everything you've said except the last part which confuses me. You say you've modded an MOT to use as a choke which works well for battery welding. If you mean that you're using several batteries to weld with, the choke will do nothing, as you've already got pure DC and is as good as you'll ever get.

Mig and DC stick welding needs a choke because that DC is derived form rectified AC and at those high welding currents, capacitors can't remove enough ripple to keep the arc voltage from dropping below the sustainability level and going out every half cycle. That's why you need a choke to sustain the arc. But you mention combining the coupling transformer and choke functions. I can't see that working because the inductance of the winding doing the coupling will be way too low to provide much choking effect, even with the ferrite core. All the chokes I've seen are quite massive, with large, heavy laminated steel cores. Here's a couple of links to sites that have made stabilizing chokes...

http://shdesigns.org/Welding/CP-250/stabilizer.jpg
http://www.instructables.com/id/Golfcart--Welder/step6/Arc-Stabilizer-and-Stinger/
http://www.vintageprojects.com/metal-welding/auto-arc-welder.html

Good luck!

Regards

dr pepper
03-02-2010, 02:44 PM
Thanks for the links.
I understand your confusion, I said stuff that shows my understanding of the application followed by something totally contradictory, however I'm not bonkers, I think we are on crossed wires.

I agree with your second comment I think you are right, I dont think now that a common output inductor and hf coupler xformer are a good idea, I'd need a very large coil to make it air core with enough inductance for mig mode, and that would also need a big high voltage cap to make it resonate at the correct freq for tig hf start, possible but impratical.

I have to argue a little about the inductor usage with batteries, if you strike up with a low impedance supply like batteries you blow the end of the rod or wire and just spray blobs everywhere due to the massive current produced, an inductance produces pinch effect, where the current rises more slowly allowing the rod/wire to melt into the job, this reduces the peak current and increases average current giving a much better penetration and less splatter, and also the inductor gives back emf on dip transfer which ups the voltage when the weld current ceases maintaing the arc, hence the name stabiliser, I got my design from one of your links.

Most altys are 3 phase so when rectifryed at full wave give a fairly smooth output with just a little ripple.

My professional mig welder does have capacitors and an output inductor.

My other interest is valve radios, and these widely use inductors to smooth the dc ht supply, probably because in the days of tubes chokes were cheaper to make than electrolytics.

siciunas
03-02-2010, 03:02 PM
Aha! Good point! In my tunnel vision view of lack of ripple from a battery, I completely ignored the effect the choke's inductance would have on the rise of current as the arc was struck and when ended. You have obviously given this more thought than I. I'm sure your project will succeed since it's obvioulsy in good hands.

As to the old valve sets (we call them tubes), I remember them well. Chokes were quite effective in filtering the DC then since though the voltage was high, (hundreds of volts) the current was low (less than a hundred milliAmps). In fact some early radios used "Dynamic" speakers, wherein the speaker didn't have a permanent magnet for the voice coil, but a wound coil, which also served as a choke for the high voltage rectified DC. I guess in those days, low frequency audio response wasn't an issue! :-)

It has been a pleasure (and enlightening), "chatting" with you.

Regards

Eugene

dr pepper
03-02-2010, 03:57 PM
Yes me too, I'm getting mellow in my age, I dont fall out with folks anymore.
About half of my valve sets have the choke in the speaker you mentioned, they did it as magnets were difficult to make, your description is spot on, some sets though had another winding that cancells the hum produced by using the coil as a choke/electromagnet.

Hardware bashing is due to start soon, large alty's are not so common in the uk, I'm still looking.

Iedd: what did you set the spark plug gaps too?, and did you solder the ht wire to the output of the coil or did you fasten it with other means.

iEdd
03-02-2010, 06:57 PM
Cool thanks for sharing that, I like your machine.
I'm not too bothered about the space, and actually I like your plan with the 'plugs in a bit of drilled and tapped steel.

Yeah, it's actually some 40x3mm aluminium flatbar. After going to the fastener shops and being told that you can't get a nut for the spark plug thread, which is M14 x 1.25, a superfine thread, I realised our tap and die set actually had one. Seeing as the aluminium conducts well (as would steel in a piece that big), the piece of flatbar connects 2 in series. There's also a small piece of pine under the centre of the bar to space it up from the floor of the case. Other than the fact that all my holes were crooked, it worked well. (We were in the process of moving house at the time, and it was a case of making do with a handdrill and almost all other tools packed away.)


What was the gap on the plugs?.
They were originally set to 0.7mm (0.028") x 4, but my new ones are only about 0.6mm x 3, and I'm getting a massive arc at the welder end - about 8mm in air, or probably close to an inch in argon! So I'm probably going to close them a little. For 4 gaps in series, 0.5mm (0.020") is probably a good starting point.


Very nice iEdd!!!!! Thanks for the links about using ignition coils. Even though I'm quite happy with my "Fly grid" transformer-based unit (for now), it never hurts to have more info available. I take it you gave up on the NST-powered version?

Thanks. :)

Yeah, my NST was the switchmode type and had all sorts of protection, including both short circuit and open circuit cutouts. It would simply switch off, and at best I'd hear a brief spark. Considering I could get the coil+cap+dimmer for a total of ~$60, it didn't seem worth it to keep trying with $120 switchmode supply. It might come in handy for something later.


The schematic didn't show any supressors, and you wouldn't want to fry your alternator diodes!

Yep, I mentioned this before about this particular schematic, and it's absolutely paramount.

The casano schematic (http://www.casano.com/projects/hfstart/index.html) seems to be made for an AC stick welder. The only time you can get away without the suppression circuitry is for a transformer type welder doing stick or TIG on AC.

If you look at the secondary side of the coupling circuit, you end up with a HFHV power supply where the terminals are either side of the coil. So one terminal is the TIG torch and the other is where the TIG torch plugs into the welder. The suppression network provides a path to the ground clamp from the TIG torch side of the welder. Without this, you will have HV going through your welder!

Edit:

did you solder the ht wire to the output of the coil or did you fasten it with other means.
I undid the screw and pulled out the little flanged bit of metal. I then took one of those automotive ring connectors and crimped it onto some 10kV wire that came with my NST. I had to bend the connector up 90 degrees, break the plastic off it, and even file the screw head down a bit for it to fit, but now I can undo it any time I like.

dr pepper
03-03-2010, 08:58 AM
Yep thanks for that iedd a good reply, a few designs I've looked at including commercial ones just have a filter cap accross the rectifryer to protect against the rf from entering the bridge and nuking it.
I have a coil off a fiat, I'll use this as my high voltage source, it has molded output connectors so I'll rob the connector of the end of the original plugs leads and use that.
I have some m14 by 1.25mm pitch threaded rod, i got the stuff for a job, but I couldnt get any nuts, so your quite right.

Just thinking a little further and doing a couple of volt-second calculations I wonder if I wound an extra coil on the mot of thinner wire whether I'd be able to vary its inductance via the saturation effect, this is what expensive commercial sets do, if I vary the voltage on the extra winding I can bring the tranny towards saturation and reduce the inductance, the good thing about it is that the tranny isnt bothered about current satuation wise, its the voltage frequency and core cross sectional area that contribute to the max magnetic flux.

iEdd
03-03-2010, 04:20 PM
Careful with the plug leads. Often they are a carbon conductor with fairly high resistance, which might stop this from working. Check with a multimeter.

dr pepper
03-03-2010, 04:35 PM
Thanks for the warning I did and they are resistive, I think most leads are nowadays to prevent emi.

Had a very interesting idea about the output choke using an mot, make the thing infinately variable, I seached the net for info and found this, most interesting, the primary coil of the mot could be rigged to a modified pc power supply primary transformer wimding to give the saturation dc supply.

http://aaawelder.com/reactor.html

iEdd
03-03-2010, 08:14 PM
Good stuff. So the rigged MOT is for a variable choke on the output of your 200A alternator? Is the main current still controlled by the amount of DC field current applied to the alternator though?

Also, you said this was for MIG/TIG/Stick, but usually MIG has a constant voltage source (like 99% of power supplies), but TIG and stick use constant current sources (vary the voltage to maintain constant current as the resistance changes). I'm not sure how much difference it makes in practice, but I'm wondering if your setup might do TIG/stick really well, but do MIG not so well, or vice versa.

dr pepper
03-04-2010, 09:00 AM
Yep I see what you mean, heres to explain.

My control board for the alty has both a current limit pot and a voltage regulation pot, so you can either adjust the pots to give constant current with adjustable max voltage, or constant voltage with adjustable max current, this means the power source is good for either mig constant voltage or tig/stick constant current.
I was thinking of having the output of the alty rectifier go 2 ways, one through a arc starter circuit as per this discussion and use that for tig mode through its own dinze socket on the front panel, and have another output go through a saturable core inductor which can connect to the mig torch and stick output, so whilst using mig and stick I'd have adjustable inductance, a range switch for the inductance might be a good idea as mig only needs a little reactance and stick needs a bit more.
Another feature I thought for the reg board is a current detect circuit, this could go through a switch so that the hf start could be off, permanantly on or auto ie switches off when the arc strikes, similar to a professional weld set.

bill south
03-04-2010, 09:38 AM
Hey Guys;
Just a quick question for the Tig Design Experts! I have a cheapie Harbor Freight Tig welder that works fine. However, it has scratch start instead of automatic HF start. What do I need to add this feature to the HF welder? Does anyone make such an add on feature within the price range of a hobby cnc shop?

Many Thanks.
Bill

dr pepper
03-04-2010, 11:55 AM
You can buy them, allthough the last one I looked at was more expensive than buying a cheaper weld set that allready had hf start.

Orvillefpike
03-05-2010, 07:07 PM
Usually, on a car ignition system, there is a capacitor in parallel with the points. When the points are open, the current from the collapsing magnetic field flows through the capacitor. Why isn't there a capacitor across the the emitter and the collector of the transistor turning the coil on and off?

Thanks

iEdd
03-05-2010, 09:25 PM
I think in a car, you are using a capacitor to suppress any transient spikes that occur from the mechanical sparking of a gap.

In the digital drivers, you have a collapsing magnetic field from the primary of the coil, which gives you a reverse EMF 'kick' of up to a few hundred volts. A diode in reverse across the transistor will short this to protect it. A capacitor wouldn't really help across the collector and emitter.

Orvillefpike
03-06-2010, 10:37 AM
The capacitor, in a car ignition I was told, is used to control the rate of discharge of the collapsing of the magnetic field in the coil.

dr pepper
03-08-2010, 06:04 PM
The condensor or capacitor is an important part of the car ignition and it can shape the envelope of the coils primary waveform.
And the circuit I looked at has nothing accross the coil, theres a diode across the source and drain of the mosfet transistor to protect it, but theres another diode in series with the tranistor which would be reverse biased and off when the coil is discharging, so I spose your both right, the circuit is not so good ans the coil will have really high reverse spikes accross it, great for someone fiddling in the basement making sparks, but not so great for reliability.
For my application I think I'm gonna fit a spark suppressor x rated cap and resistor module accross the lt of the coil (same as accross domestic appliance motors), which is a module containing a 0.1uF cap and a 100r resistor, just to keep the voltage on the primary within the capbilities of the coil and to stop uneccessary rf interference.

iEdd
03-08-2010, 06:20 PM
In the RMCybernetics link I gave you, there is a cap+resistor across the coil. That's a good thing. A cap across the transistor would be a bad thing.

dr pepper
03-08-2010, 08:26 PM
Normally I'd agree with that, the subject seems to be one for conjecture though.
Heres a link to a photo of my coil driver circuit completed, just above the snips to the right is the arc produced accross a couple of pieces of tig wire, the sound produced is quite loud.
If I cap the coil the spark goes nearly altogether, the reverse spikes are within the rating of the 1n4005 I used, an am radio nearby doesnt seem to be affected.
Maybe I'll just put a transzorb accross the coil at a little lower voltage rating than the 1n4005, it seems that the coil 'likes' being open circuit.

http://www.landyzone.co.uk/photopost/showphoto.php?photo=14901&size=big&cat=&ppuser=32763

Theres a circuit around called a megasquirt, or more appropriately megasquirt and spark, its a home made engine management system, I'll see if I can get a schmatic of the coil firing circuit and see how they do it.

dr pepper
03-09-2010, 07:15 PM
Ok then so I have made the ignition coil driver circuit, and the tank coupling coil and tank cap, the tank coil has 10 1 inch interference suppressor type ferrite cores on the inside, held together wilth heat shrink, theres a layer of heat shrink between each winding, the tank cap isnt a doorknob, I used 20 2kv 10nF caps in series to make 500pF at 40KV, the caps were only 15pence each, I changed my freq from 300k to 1meg, I heard on this thread further up that someone had used test gear to determine the resonant freq of the coil/cap, I have the gear so I tried this, simply by connecting a 10k resistor inline with the sig gen accross the tank coil/cap and connecting the scope at the same point, and according to the scopemeter I'm close, the coil and cap resoantes at 1.3 meg.

Heres some pictures.
Getting impatient now as I still dont have an alty, I'll try this arc starter with my buzzbox first though, to make sure it does as it should, th ign coil I used is a more modern twin spark job, its a small thing but appears to work well.


http://www.cnczone.com/gallery/data/500/medium/Picture_147.jpg

http://www.cnczone.com/gallery/data/500/medium/Picture_136.jpg

Orvillefpike
03-15-2010, 01:53 PM
Dr. Pepper,

Are you driving the ignition coil at 120V or 240V?

dr pepper
03-16-2010, 02:23 AM
12vdc via a variable pwm driver.

Raban
07-06-2010, 06:20 AM
If anyone interested, here is' the beginning of an open source project for an inverter tig welder ac dc

http://meccanicaedintorni.morpel.it/phpbb/viewtopic.php?f=75&t=3817

kaighn80
07-07-2010, 03:56 PM
well i think it needed resurecting as i would love to build a tig welder so has anyone finished theirs yet and if so do you have a diagram?

dr pepper
07-08-2010, 04:14 PM
Mine does work now, only its not as intended driven by a alternator, its powered from a stick welder, HF works ok, and variable power control works ok, I had a bit of troublwe with the tranny getting warm, you have to be carefull how you arrange the trigger circuit for the triacs, as if the triggering isnt symetrical, the resulting harmonics and DC nukes the tranny.
I'm working on a schematic.
The protection for the rectifier is no hard task, a power factor correction capacitor from a scrap fluorescent tube fitting does the job nicely.

kaighn80
07-08-2010, 06:04 PM
cool im looking to build one from a dc stick welder as im not that interested in welding ally so steel and stainless only are there any differences between the two or will i build it exactly the same as if i was using an ac stick welder? sorry if this is a dumb question but i have no background in designing anything electronic, im purely a if it dont fit trim it if its too small recut kind of person, given a diagram i can pretty much build anything but i dont understand enough of this sort of thing to work it out for myself. previous projects include a mini crewcab pickup, mini roadster, mega squirt ecu, 3 axis cnc machine and a few bikes. if at all possible and you have it could i have a copy of the diagram for the tig youve built so as i could build my own please. thanks in advance.

moking
07-09-2010, 11:42 AM
I would like to use a stick welder as the power source for a TIG converter. The problem is the Stick O/P is AC and the requirements for the TIG converter are DC minimum voltage 50V. I take it a standard Bridge rectifier of 200A at 400v would suffice and can I do without any smoothing or does the rectifier require some capacitance as protection on back EMF. All info would be most welcome, especially from you guys that have been there and got the T shirt so to speak.
Best Regards
Mo King UK Ex-Pat in Spain

dr pepper
07-13-2010, 05:22 PM
You dont have to use smoothing caps, allthough if you do you'll have better pen, as the average DC voltage will be higher, but try without first.
If you use an arc starter on a DC set, then its important to use a capacitor accross the DC output of the rectifier to stop the RF comming back and toasting the rectifier, a 20uF motor start cpacitor, or a fluorescent light capacitor is fine.
Heres a link to a cool start box, this ones dead easy,


http://www.casano.com/projects/hfstart/index.html

To make a AC welder DC you need the rectifier as mentioned, and the capacitor, a fairly simple setup, with the DC stick welder all you need is the capacitor accross the output and the arc starter.

dapug
07-16-2010, 06:44 AM
Hi
It was nice to read about your effort to make a tig welder.
I noted that you had problems with the tramnsformer supporting the current
after the arc has been struck.
I can only see that you have nothing to limit the arc current except for the impedance of the transformer.
Since the transforme rimpedance is usually quite low and the atc resitance is quite low as well a very large current will flow upon starting the arc.
This may blow your fuse, scr or damage the transformer.
You need a current limiting choke in series with the + or - lead of the rectifier output.
This choke may turn out to be as large as the transformers themselves depending on the max current you design them for.
Best Regards
AG

electric2u
07-17-2010, 06:41 AM
question maybe wroung place,
Steel tubing verise aluminum on building a cnc. the spectes i see say the steel wall can very .020 or so. the bigges problem is i have a welder, but nothing to weld aluminum with. what are you thoughs on staightness on this.
thank you, kevin

dr pepper
07-25-2010, 01:57 AM
Dapug yes thats correct, mine uses thyrister burst firing to control the current.
If an arc welder transformer is used then this is less of a problem, as arc transformers, well cheaper ones that is, have a magnetic shunt, or an air gap which significantly increases the output impedance.
Theres a geyser on the web that has built a variable reluctance saturable core inductor to regulate the output of a welder using microwave transformer, if anyones interested I'll post the link.

Electric2, I dont think 20 thou variance is going to be an issue, esp if the weld is moving, if your welding something like 1mm then 20thou wont make a huge diffo.

kaighn80
07-25-2010, 03:44 AM
[QUOTE=dr pepper;803289]Dapug yes thats correct, mine uses thyrister burst firing to control the current.
If an arc welder transformer is used then this is less of a problem, as arc transformers, well cheaper ones that is, have a magnetic shunt, or an air gap which significantly increases the output impedance.
Theres a geyser on the web that has built a variable reluctance saturable core inductor to regulate the output of a welder using microwave transformer, if anyones interested I'll post the link.

im interested!!

dr pepper
07-26-2010, 08:42 AM
Ok I searched through my links and found it, doesnt look as though the guy has finished it.

http://aaawelder.com/reactor.html

I made one rough, it does work allthough the control side seems very sensitive, I never progressed past a lashup with it.

The guy does respond to mails, send him an emither, unless he's reading now.

kaighn80
07-29-2010, 04:55 PM
ive converted my stick to tig, im having to scratch start which is a pig but im also using co2 as i have it already for the mig set, does any of this sound worrying yet?

kaighn80
08-12-2010, 04:43 PM
not long ago i found a document on 't' interweb, it was the design for an ac/dc tig welder but i don't speak polish so i couldn't read it, long story short i used google translate to join a polish website and found the guy who designed it, after a couple of emails again translated because he doesn't speak english he sent me the whole article. problem is its in polish and when i try to translate it its literal so quite a lot of it doesn't make sense.

moking
08-13-2010, 01:31 PM
Hi kaighn80,
Many thanks for the message. Is there any possibility of sending me a copy of the Polish article as Electronics doesn't recognize any language barriers.
moking_BSc@hotmail.com

Bebetto
09-03-2010, 11:22 PM
Hello, I am new to this forum and I have some questions about TIG welding. What is the required frequency to tig weld? If I have an inverter 240A max, DC voltage output with pwm, 0-50% duty cycle, about 30V on the output at a frequency of 40KHz, would this work for tig welding? Why do you need ac voltage for aluminum? Any thoughts are welcome, thanks.

packrat
09-04-2010, 12:15 PM
The AC for Tig welding aluminum is to keep the oxides out of the weld puddle.

jdchmiel
09-24-2010, 02:00 PM
I just found this thread and am quite excited as I am doing about the same exact project!
I picked up 2 crown vic police 200 amp alternators for $55 each on ebay :) They are interesting in that you can adjust the output via the ECM control from 12v to 16 v via a 125hz pwm signal of 5-100% duty cycle. I was next looking at large diodes to protect the alt from a hv starter circuit... I dont know electronics to the same level as you guys, but as soon as someone said cap across the rectifiers it madde sense and I realized the $22 diode would not be needed (300A 800 volt diode yummm: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=260614722488&viewitem=&sspagename=STRK%3AMEWAX%3AIT)
So anyways, The HF starter seems pretty straight forward.. I will just need to do a lot of testing and scoping oncce I build it to be sure I do not kill my diodes in the alternator(s).

I had been contemplating using the 12-16v regulation these have built in for a CV power source, and maybe some way to bypass them to feed the field current directly with the same PWM signal ( something similar to this http://www.rmcybernetics.com/shop/cyber-circuits.htm#A21) as a CC power source, but I am a bit hazy on CC and how this would actually work.. From what I have read people successfully built welders from alternators all the time using a variable supply directly to the field coils, but Is this actually CC or not? Does the current into the field dictate the max current the alt can generate, and the voltage just vary in accordance to that?

dhruvpandit
10-09-2010, 09:39 AM
hi there,
i am from india, and having almost zero knowledge in electricals.
but i have made a homemade air compressor from fridge's compressor.
and want to build a tig welding machine for my bike building work.
i want to make it from a car alterneter (starter ).
so pls guide me or give some schemetic diagrame for it.

i already have a electric welding machine, is it possible to make a tig weling from it?

gfioro
01-19-2011, 02:46 PM
Hi, I've built another version of the arc starter, based on the original from this thread and the one in High-Frequency Start Box (http://www.casano.com/projects/hfstart/index.html) (in which the schematic seems to be wrong, since its different from pictures of the unit made, and didn't work for me, until corrected to be like in pictures).
I tried to go low cost and quick assemble so you might see lots of zip ties and vinyl tape; Also did it on an auto ignition coil because I already had it, and could make the dimmer easily.

The resonant tank capacitor is made of 9 (originally 10) 1nF 1600Vdc capacitors in series (U$S 6 total) because i couldn't get a doorknob cap, resulting a cap about 0,1nF 14,4KV. Most designs I've seen work on 30KV (or more) caps, but it seems that if you dont ask too much, 14KV is OK.
Perhaps the reason these have not fried yet is the regulation of the spark gaps, that in this circuit should act as voltage limiters (some say 3KV/mm of gap others 1KV/mm, the last worked better for me), which at 2 series x 3mm (6KV eq.) worked well. Another possible reason is ignition coils delivering less power than neon sign transformers, somewhy, but it's only a thought.

I first packed the caps in parallel lines of three, insulating them with pressphan paper, but insulation failed so I later put them in 1 line around a PVC pipe, with thick pressphan stacks (kind of separation rather than insulation) to insulate from box and nearby components.

Spark gaps are steel wire on a bakelite electrical connections base. The power demanded didn't seem to wear electrodes, but still I made electrodes so that they have large working areas rather than being needles, so that even if wear occurs, the spark can move aside without varying breakdown voltage. I built the prototype spark gap on MDF board, but as expected, the HV burned the wood.

The inductor of the tank circuit is made of about 10 turns of thin 600Vac wire in only one layer, so that the mere distance between input and output acts as insulation (voltage between turns should be at most 6KV/10= 600Vpk, which is OK for the insulation the cable provides between turns). I wrapped the entire winding in duct tape and some layers of pressphan, mainly to insulate from box and secondary. I used a yoke from a 15"CRT as the core (Its tricky to wound the secondary in there, but i preferred it as i think it should decrease RF emissions). I used 10mm2 600Vac wire as secondary, and insulation seems to resist the full output voltage.

Suppression caps are made just as in the one in this thread, but with bleeding caps (4,7Mohm on each cap.). I tested the suppressor with an inverted pair of 1N4007 in series, as they break at 1Kv, less than my rectifier (1,2KV).

Next step will be a SCR power regulator + MOT arc stabilizer (choke?)

Hope this experience provides useful info, and I’m greatly thankful for all what i've learned from this thread!

iEdd
01-19-2011, 05:53 PM
Looks pretty good, gfioro.

I didn't use the casano circuit either. I just used the idea of dimmer+cap+coil and then wired it just like the Miller HF box.

Interesting you went with the toroidal coupling transformer. It might provide better coupling, but I thought it looked a bit hard to do, so I just did the cylindrical PVC pipe style like the original arcstarter. I'd be interested to hear how it goes when everything's finished.

Raban
02-27-2011, 11:04 AM
our plan of ac dc tig welding works, I put the video link test stage DC, in the forum there are all the schemes
MECCANICA e DINTORNI • Leggi argomento - Scheda Gate driver and primary switch (http://meccanicaedintorni.morpel.it/phpbb/viewtopic.php?f=76&t=4235&start=120)
YouTube - Video-0004.mp4

Raban
04-30-2011, 05:37 AM
HF/HV stage working
see here

YouTube - Accoppiamento serie - prova 2

kaighn80
04-30-2011, 12:17 PM
so does any one have a full working design for a ac/dc tig welder that isnt made of unobtainium and buildable for less than the cost of a mass produced tig welder as my bike is nearly done now and i need another project.

Josue Tortola
02-15-2012, 11:14 PM
Hi Guys!!!
This is my first post here and want to thank all of the people that took time, effort, patience and knowledge to share it with all of us.
This is a really good thread....I learned a lot reading it and a have some thoughts.
Let´s suppose that we are not looking for High Frequency...let say that we are just looking for High Voltage so we can start the stick electrode and tig electrode without scratching it using a dc stick welder .....this is ok for welding steel....the High Frequency is only needed for aluminum.
The question is this.
Can we just use the lamp dimmer, capacitor and car ignition coil to start the electrode (tig and stick) without scratching it?
Has anybody done this before?
If it is possible does the suppression circuity that is has been outlined here is enough or must be modified?

Thank you all!!!

gfioro
02-16-2012, 02:20 PM
The HF current used in an arc starter is not the same as the HF in the weld current; arc starters deliver vary little current at a voltage enough to ionize the gas, while HF AC welding current is large (so as to deliver power/heat) at a lower voltage (i guess it´s always below 100V). Besides, arc starters usually work on megaHertzs while HF welding currents are probably around kiloHertzs.

The polarity of the welding current determines which electrode heats the most, and directs migration of ions between them, through the arc; the positive electrode (if i'm right...) receives both the most heat and the oxides (i guess it´s the oxigen anions that travel) . When we weld stainless steel or steel, oxides either fuse along with metal and flock, or are at a little amount, so making the workpiece the positive electrode is okay. When we weld aluminum, it always has a relatively thick layer of oxide which fuses at a temperature much higher than the metal, so it stays as a "bag" of oxide around aluminum and disturbs the welding puddle. If you invert polarity, the tungsten electrode will attract oxides and clean the aluminum, but it will overheat and melt (i tried it...), so a good choice would be changing polarity shortly and periodically during weld, at a frequency high enough to keep the arc hot and stable, and at a rate enough to balance cleaning with electrode life. I guessed some of that, so it might be wrong... but it makes sense to me :P

I haven't found out if HF is necessary to start an arc; perhaps HV DC is enough, as in van der graaf generators. My best guess is that it is very difficult to build a HV DC starter circuit that works and doesn't burn the electronics/isolations inside the welder (it would be practically impossible to build it in series to the welder, and if you put it in parallel, the welder will absorb it -and fry-), whereas a HV HF AC circuit can be installed in series with the welder, and its current bypassed from the welder with the supressor.
In other words: because of the great difference in frequencies, arc starting and welding currents can be mixed in a same wire and then filtered as required, with capacitors and inductances of reasonable sizes. I guess that is the main reason to use HF arc starters.

I tried to build an arc starter -with some degree of success-, but it stopped working probably due to capacitors or car ign. coil being fried in a spark gap length experiment; if you try to reproduce my prototype (its in this thread, same user name), do not trust in the exact values i used :P

Sorry for my bad english...
Good luck!

Josue Tortola
02-16-2012, 04:59 PM
gfioro!
Thanks for the detailed explanation!!
This is very interesting:
In other words: because of the great difference in frequencies, arc starting and welding currents can be mixed in a same wire and then filtered as required, with capacitors and inductances of reasonable sizes. I guess that is the main reason to use HF arc starters.


By the way does anybody knows the frequency at the output of a car ignition coil driven by a lamp dimmer? I know the lamp dimmer chops the 60 Hz coming from the mains and this is what causes the oscillation to create the spark at the output of the car ignition coil so the frequency should be 60 Hz or am I wrong?

I am sorry to hear that your HF unit is not working anymore and I would like to hear that you will repair it.

I haven't found out if HF is necessary to start an arc; perhaps HV DC is enough

The HF is definitely going to start the arc.... and HV DC is also going to start the arc and I have done this with my welder (AC DC stick welder 55/250 Amps). I have 47 DC volts OCV but if I add a cap at the welders output (in parallel) the OCV goe to 80DC Volts and I just have to make contact with the metal work to start the arc....the problem is that the weld gets too hot, too liquid at the minimum amp setting....that´s why I was asking the question about the lamp dimmer, cap and car ignition coil but according to what gfioro says this is going to burn something.

Any other thoughts are welcome!

kaighn80
02-16-2012, 05:26 PM
so does anyone have a working schematic they could share please, i have the polish one that does ac/dc but i cant make heads nor tails of it.

gfioro
02-16-2012, 09:04 PM
Kaign80: there are some open designs, as the one Raban offers and others in this thread. You can look at this one also, TIG_Welder_Project (http://www3.telus.net/public/a5a26316/TIG_Welder.html). I think that you won't be able to build a HF AC (for aluminum) welder at a lower cost... you will probably spend less money on the final components, but you'll work a lot, and spend a lot in experiments and tools!
You might build a DC TIG on the cheap if you take an AC stick welder, add a rectifier and a torch + argon tube + argon pressure & flow regulator (argon tubes work at very high pressure). That is what we did in my home, and it works! Our welder didn´t have an efficient current regulation so it was tricky, but we sorted it out.
Some people even make the transformer out of microwave oven transformers (MOT), and regulate them with huge dimmers.

Josue: We bought a DC TIG welder after that last experiment, so i haven´t worked on that circuit anymore... we use the welder for work so it was worth the cost!

I first tried putting the car ign. coil in parallel with the old welder output, and made the most expensive experiment so far; Doing that, i applied HV "kicks" of about 6-30KV to the welder's rectifier bridge, and luckily only burned one diode...
In your case, the capacitor might dampen the HV and save your bridge (also, it may not), but at the same time it will dampen the HV output. It might work, but it's a risky gamble. Furthermore, if you pierce the capacitor's isolation, it might short the welder, boil and explode, as electrolytic capacitors have liquid inside.

An auto ignition coil fed with a dimmed 120V 60HZ will deliver bursts of HV AC; it´s a HV transformer fed with "pieces" of 60Hz AC current. The output will be a sort of 60Hz + perhaps some noise; It, by itself, is not capable of generating much HF. If I've understood well, the spark gaps + capacitors + HF transformer winding make a HF HV resonant circuit which do the work. The auto coil is like a hammer, and the rest is kind of a bell. The HF transformer is air cored or ferrite cored, both of wich transmit HF rather well but 60Hz pretty bad, and can be made with few turns on the secondary, so that you can use heavy gauge wire without trouble; that way you can induce HV in series with the welder//supressors, not burn the welder nor the arc starter, and still create a spark between electrodes.

You need about 1-3KV to make a spark through 1mm of fresh air, so i think the improvement in your welder's start is due to the capacitor giving lots of power by itself during the electrode touch, in a kind of explosion; i'm not sure how that would work on TIG.
If you want less power during weld, you might try putting a smaller capacitor, or 2 of them in series. You can also add a huge dimmer to control the welder, but it depends on how your welder is built.

bye!

Josue Tortola
02-16-2012, 11:03 PM
gfioro!!!!
You might build a DC TIG on the cheap if you take an AC stick welder, add a rectifier and a torch + argon tube + argon pressure & flow regulator (argon tubes work at very high pressure). That is what we did in my home, and it works!

That is exactly what I did....I added rectifiers and an inductor to my AC Stick welder and the difference to start the arc was evident....I haven´t bought the torch, the hose, the regulator etc. but this is going to work for sure.
Right now I am not using the capacitor (400V 180mf electrolytic cap) because the inductor is giving me a really nice weld bead...I did use the capacitor immediately after adding the bridge rectifier and started the arc just by touching the metal work but the weld bead was a mess....I must say that I usually weld material between 1/16 and 1/8 of an inch and I felt that the weld bead was as I said before too hot so when I built my inductor I did it with 14 gauge wire because I wanted some resistance....my inductor was wounded in a UPS transformer...is not a large inductor but works really good (I least for what I weld)

I first tried putting the car ign. coil in parallel with the old welder output, and made the most expensive experiment so far; Doing that, i applied HV "kicks" of about 6-30KV to the welder's rectifier bridge, and luckily only burned one diode...
In your case, the capacitor might dampen the HV and save your bridge (also, it may not), but at the same time it will dampen the HV output. It might work, but it's a risky gamble.

Thanks for sharing the above info so I can take my precautions or totally forget the idea.

If I've understood well, the spark gaps + capacitors + HF transformer winding make a HF HV resonant circuit which do the work. The auto coil is like a hammer, and the rest is kind of a bell. The HF transformer is air cored or ferrite cored, both of wich transmit HF rather well but 60Hz pretty bad, and can be made with few turns on the secondary, so that you can use heavy gauge wire without trouble; that way you can induce HV in series with the welder//supressors, not burn the welder nor the arc starter, and still create a spark between electrodes.

What a nice explanation!!!!!!! Thank you again!!!

You can also add a huge dimmer to control the welder, but it depends on how your welder is built.

My welder is 120/220 V (can work either way)55/250 Amps. The transformer is variable...it has a piece of metal (I think in english is called shunt)that goes in and out of the transformer via a knob that is rotated.
How many amps or how may watts should be the dimmer?
As I have read and understood the dimmer must be connected before the primary....is that right?

Sos de Argentina?

Thank you very much gfioro!!!!

gfioro
02-17-2012, 10:21 AM
Jaja si, soy de Argentina. Vos de Guatemala? Eso dice el usuario :P

By "argon tube" i meant the high pressure vessel, the tank, which in our case works at 140 bar of pressure. Argon regulators often deliver 5 bar, and some can be setted to lower pressures. If you don´t have it, consider it can be expensive.

Adding a dimmer is something electrically "incorrect" but works; I´ve seen commercial welders with them. A dimmer for a welder should be designed for inductive loads. And yes, dimmers work better at the primary, because of the lower currents.
If you make or buy a dimmer, remember that their cases, heatsinks and even perhaps knobs can be connected directly or somehow to the mains (TRIAC and SCR heat dissipation tabs are often connected to a terminal), so electrocution risk is high.
*** BE VERY CAREFUL! *** , don't take risks and don't use it if you don't fully understand it. Ask the seller for the dimmer's instalation procedure or standar housing, also.

Here's a homemade design: Homebuilt arc welder · Dan's Workshop Blog (http://www.dansworkshop.com/2008/03/homebuilt-arc-welder)

Selecting voltage capability of a dimmer or its components is not so hard: If your mains is 220V, that is it's RMS value, kind of a power equivalent to DC voltage. If you want to select a SCR/TRIAC, it´s datasheet will probably specificate peak voltage; sine wave AC has a peak voltage of 1.41 ( = sqrt(2)) the mains RMS voltage: 220Vrms * 1.41 = 311Vpk, so any 400Vpk component should work okay.... at least from what i know.

The current capability of the dimmer needed to control a welder is a bit hard to estimate, at least for me. First of all, you should look at the plate of the welder and try to figure out peak primary current, "I1max" probably.
If that is impossible, you can measure the current with a clamp inductive amp meter, and try every possible use (vary power, weld with a long arc, a short arc, and stick the electrodes in short circuit). As a last resource, you can calculate power output of your welder, calculate amps needed at the primary, and apply a generous safety coefficient. Stick welders usually deliver around 20V at medium amperages, TIGs are around 14V @ 30A. Be warned that welder are highly inductive loads, so their power factor is poor and draw extra current that flows but -due to not being in phase with voltage- does not deliver active power; that means that a welder delivering 2200W@220V will need 10 amps of "active" current and some more (some times a lot more) of "reactive" current... if the welder data plate specificates power factor or Cos(phi), you can calculate the reactive current.

Safety considerations and design of the circuit can be found in many websites.. google it. Again, be careful -even if you just buy it- and don't use it until you fully understand it. Take into account the heat dissipation requirements of the dimmer, they dissipate about P = 1.5 Volts * I ... if i'm right.

If the result goes up many amps, it can be too expensive, so you might consider using a smaller but detachable dimmer, only when requiring low power, and protect it with a fuse or thermomagnetic switch (it might not be enough, but it's something). I´ve seen a commercial welder with a rather small triac.

bye!

Josue Tortola
02-17-2012, 10:33 AM
Si soy de Guatemala!!!! Saludos!!!
As is said in your country "Sos un monstruo vos" thank you very very much for everything!
Have a nice day!!

burt007
03-15-2012, 04:27 AM
Here is the whole plan for free.

Access point (http://www.filecrop.com/10623736/index.html)

burt007
03-15-2012, 04:30 AM
Here is the pdf file for free.



Jaja si, soy de Argentina. Vos de Guatemala? Eso dice el usuario :P

By "argon tube" i meant the high pressure vessel, the tank, which in our case works at 140 bar of pressure. Argon regulators often deliver 5 bar, and some can be setted to lower pressures. If you don´t have it, consider it can be expensive.

Adding a dimmer is something electrically "incorrect" but works; I´ve seen commercial welders with them. A dimmer for a welder should be designed for inductive loads. And yes, dimmers work better at the primary, because of the lower currents.
If you make or buy a dimmer, remember that their cases, heatsinks and even perhaps knobs can be connected directly or somehow to the mains (TRIAC and SCR heat dissipation tabs are often connected to a terminal), so electrocution risk is high.
*** BE VERY CAREFUL! *** , don't take risks and don't use it if you don't fully understand it. Ask the seller for the dimmer's instalation procedure or standar housing, also.

Here's a homemade design: Homebuilt arc welder · Dan's Workshop Blog (http://www.dansworkshop.com/2008/03/homebuilt-arc-welder)

Selecting voltage capability of a dimmer or its components is not so hard: If your mains is 220V, that is it's RMS value, kind of a power equivalent to DC voltage. If you want to select a SCR/TRIAC, it´s datasheet will probably specificate peak voltage; sine wave AC has a peak voltage of 1.41 ( = sqrt(2)) the mains RMS voltage: 220Vrms * 1.41 = 311Vpk, so any 400Vpk component should work okay.... at least from what i know.

The current capability of the dimmer needed to control a welder is a bit hard to estimate, at least for me. First of all, you should look at the plate of the welder and try to figure out peak primary current, "I1max" probably.
If that is impossible, you can measure the current with a clamp inductive amp meter, and try every possible use (vary power, weld with a long arc, a short arc, and stick the electrodes in short circuit). As a last resource, you can calculate power output of your welder, calculate amps needed at the primary, and apply a generous safety coefficient. Stick welders usually deliver around 20V at medium amperages, TIGs are around 14V @ 30A. Be warned that welder are highly inductive loads, so their power factor is poor and draw extra current that flows but -due to not being in phase with voltage- does not deliver active power; that means that a welder delivering 2200W@220V will need 10 amps of "active" current and some more (some times a lot more) of "reactive" current... if the welder data plate specificates power factor or Cos(phi), you can calculate the reactive current.

Safety considerations and design of the circuit can be found in many websites.. google it. Again, be careful -even if you just buy it- and don't use it until you fully understand it. Take into account the heat dissipation requirements of the dimmer, they dissipate about P = 1.5 Volts * I ... if i'm right.

If the result goes up many amps, it can be too expensive, so you might consider using a smaller but detachable dimmer, only when requiring low power, and protect it with a fuse or thermomagnetic switch (it might not be enough, but it's something). I´ve seen a commercial welder with a rather small triac.

bye!

burt007
03-15-2012, 04:31 AM
Here is the pdf file for free.
Access point (http://www.filecrop.com/10623736/index.html)



Jaja si, soy de Argentina. Vos de Guatemala? Eso dice el usuario :P

By "argon tube" i meant the high pressure vessel, the tank, which in our case works at 140 bar of pressure. Argon regulators often deliver 5 bar, and some can be setted to lower pressures. If you don´t have it, consider it can be expensive.

Adding a dimmer is something electrically "incorrect" but works; I´ve seen commercial welders with them. A dimmer for a welder should be designed for inductive loads. And yes, dimmers work better at the primary, because of the lower currents.
If you make or buy a dimmer, remember that their cases, heatsinks and even perhaps knobs can be connected directly or somehow to the mains (TRIAC and SCR heat dissipation tabs are often connected to a terminal), so electrocution risk is high.
*** BE VERY CAREFUL! *** , don't take risks and don't use it if you don't fully understand it. Ask the seller for the dimmer's instalation procedure or standar housing, also.

Here's a homemade design: Homebuilt arc welder · Dan's Workshop Blog (http://www.dansworkshop.com/2008/03/homebuilt-arc-welder)

Selecting voltage capability of a dimmer or its components is not so hard: If your mains is 220V, that is it's RMS value, kind of a power equivalent to DC voltage. If you want to select a SCR/TRIAC, it´s datasheet will probably specificate peak voltage; sine wave AC has a peak voltage of 1.41 ( = sqrt(2)) the mains RMS voltage: 220Vrms * 1.41 = 311Vpk, so any 400Vpk component should work okay.... at least from what i know.

The current capability of the dimmer needed to control a welder is a bit hard to estimate, at least for me. First of all, you should look at the plate of the welder and try to figure out peak primary current, "I1max" probably.
If that is impossible, you can measure the current with a clamp inductive amp meter, and try every possible use (vary power, weld with a long arc, a short arc, and stick the electrodes in short circuit). As a last resource, you can calculate power output of your welder, calculate amps needed at the primary, and apply a generous safety coefficient. Stick welders usually deliver around 20V at medium amperages, TIGs are around 14V @ 30A. Be warned that welder are highly inductive loads, so their power factor is poor and draw extra current that flows but -due to not being in phase with voltage- does not deliver active power; that means that a welder delivering 2200W@220V will need 10 amps of "active" current and some more (some times a lot more) of "reactive" current... if the welder data plate specificates power factor or Cos(phi), you can calculate the reactive current.

Safety considerations and design of the circuit can be found in many websites.. google it. Again, be careful -even if you just buy it- and don't use it until you fully understand it. Take into account the heat dissipation requirements of the dimmer, they dissipate about P = 1.5 Volts * I ... if i'm right.

If the result goes up many amps, it can be too expensive, so you might consider using a smaller but detachable dimmer, only when requiring low power, and protect it with a fuse or thermomagnetic switch (it might not be enough, but it's something). I´ve seen a commercial welder with a rather small triac.

bye!

toolmanx
04-03-2013, 07:52 PM
I was reading through your forum and I thought you guys might be interested in my project. I bought a defective Chinese TIG welder on E-bay and repaired it. I bought it because it had an inverter in the front end. I had hoped that I could just bring out the A/C output from the inverter and do thin aluminum welding.

I originally lifted the center taps on all 4 secondaries on the 2 output transformers. (They use 2 output transformers in parallel). I checked the phases of the secondaries and tied all 4 in parallel. The biggest problem I faced was converting all the control items from the original DC output to work the same as it was now seeing in A/C. I solved that problem by simply rectifying the A/C for the control inputs. When done I had perfect PWM control and could vary the intensity of a large flood lamp load from almost out to so bright I thought I might blow the bulb. The spark starter worked great and I thought I had successfully pulled it off.

I set up my gas and tried to weld on a scrap piece of thin aluminum. I barely got enough current to carry an arc. I then hooked up (5) 1 ohm wire wound resistors in series so I could read the voltage drop at full short to see how many amps I was getting. At full PWM setting I was developing 12 amps RMS. I couldn’t pull a sick prostitute off a pot with that kind of amperage. With a huge amount of labor I then put my welder all back to the original DC TIG to see if it was still working. I accidentally bumped my TIG torch to the plate I was using to make a dead short on the line for testing and it blew a hole in the plate. Plenty of amps back. I measured it and got as much at full low as I got from full high using the A/C.

I then experimented thinking maybe I was loosing some thing in the transformer windings. I tried one secondary with the others just swinging in the breeze. I lost about ten percent of what I got with all four in parallel. Then I put each transformer secondary and its sister in parallel and put the two doubles in series for higher output voltage. I still ended up to low for welding.

I then gave up this approach and decided to pulse the secondary DC to give me the A/C I needed. I have engineered a pretty good looking system with one major obvious problem I haven’t come up with a fix for yet. The pulsing MOSFETS carrying the high current are expensive and I don’t want to fry a bunch of them. They will be hit by the very high voltage and frequency of the spark starter. I don’t know how to handle that yet.

Any ideas?

I don't get to much time to get back to forums. If you would like to discuss my project or see my latest proposed diagram e-mail me directly.

Toolmanx@peoplepc.com

jurgen4
08-26-2014, 07:09 AM
anybody have plans about to build tig welder ?
Regards.

55 dude
10-22-2014, 11:37 AM
cool idea!