Reply with QuoteEXCELLENT! I'll be looking forward to reading your posts.
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.
Last edited by punisher454; 09-11-2008 at 03:12 AM.
EXCELLENT! I'll be looking forward to reading your posts.
I'll second that!Pics are always very welcome.
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.
Amy word on your build?
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 :-(
Last edited by marcgvky; 12-08-2008 at 11:55 AM. Reason: Didn't want to be rude
Not yet, I have most all of the parts, just need a little time to work on it. Soon I hope.Punisher, any word on your success?
I don't know if it would be any use but I have a schematic for my tig?
Spark plugs are fine.
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.
Last edited by iEdd; 12-25-2008 at 02:43 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!
Uh... ****. I bought "resistor type" Champion spark plugs on eBay.Originally Posted by OrionBlade2003
Will all NGK spark plugs work? I assume I need 4 of them.
If all you have...
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.
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.
I'll have to look at the drawing...
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.
Aww, hell!
You're talking about the copper block in the upper right hand part of the enclosure?
http://www3.telus.net/public/a5a2631.../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
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
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!
Low MHz preferably. I think they can be from about 100kHz to 10MHz...
Just a word of caution...
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
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.
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.
Pics?
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@$$.
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