Hi everyone,
New to the board, built my new foam cutter using Hobbycnc board and motors, but am having trouble with building the power supply out of a computer power supply. Anyone with experience in this care to helo me out a little?

Walt

Walt,

Hi! Not sure I can help at all, but maybe you can elaborate a little about what you've done, what your looking for or expecting, etc. Fill us in...

Lance

Well I tried to convert a pc power supply per the instructions from hobbycnc, but I am not getting any power at all. I am a little confused as to what kind of power supply it is, at or atx as the computer I got it from says it is a atx but I looked up the part # on the internet and it says at. Atx power supplies also are supposed to have a green wire and the only green one that I see is the ground wire. I have not installed a switch yet either which may be the whole problem but I do not know which wires to hook up to the switch. Any clue?
Thanks
Walt

Walt,

Sorry, but no, I haven't a clue. But there's bound to be someone here who can help...hang tight. And good luck!

Lance

Thanks I hope so I got airplanes to get cut!

Walt

whats the voltage for this hot wire, how many amps does it need,
does it need to be adjustable,
does the power supply work ( tried it with a computer)
are you activeting the power good line on the power supply.
does the fan turn.
did u try it with an old hard drive or something like that plugged it.
did u put a volt meter on it to see if u get 3.5, 5, 12 volts.
ps: these psu's are small, quiet , but they can kill you, be carefull.
let us know

Maybe it will be help you.It is the electrical circuit of a power supply for a foam cutter.
http://nsrca.org/technical/tip_tricks/foam_cutter/foam_cutting_power_supply.htm

a computer power supply is not a good replacement for this foam cutter power supply.
look around at electrical places or ask the guy in the next electric contractor truck you see stopped. ask for a 24v controle transformer at 2 amps or more.
if you are lucky $15.

Folks,
The power supply is for the "CNC" control. NOT the BOW power supply. 12VDC is more than adequate for this purpose.

Dave Rigotti
HobbyCNC.com

I suspect this (http://www.rcgroups.com/forums/showthread.php?t=182628) is what your after.

All the best

Barry

OK Dave, What about a power supply for the bow or hot wire? I've seen everything from 600 watts to 800 watts needed to use a 8' wire or to run 2 wires.

Thanks.

http://wiki.ehow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

this should answer all your computer power supply questions.

http://wiki.ehow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-Supply

this should answer all your computer power supply questions.


Thanks for the info.

I used a Wal-Mart 6 amp battery charger for my Motor Power supply. It will provide anything from about 6 to about 34 volts depending on how you wire it. It comes with a switch for 6 and 12 volt settings. You can easily tap off the transformer with a full bridge rectifier and a smoothing capacitor for voltages higher than 12. I've been using one for the last 6 months or so to run 3 motors at about 1.5 amps each with chopper driver boards. This is not a regulated power supply but it works great for chopper boards since the current is regulated by the chopper anyway.

I used a Wal-Mart 6 amp battery charger for my Motor Power supply. It will provide anything from about 6 to about 34 volts depending on how you wire it. It comes with a switch for 6 and 12 volt settings. You can easily tap off the transformer with a full bridge rectifier and a smoothing capacitor for voltages higher than 12. I've been using one for the last 6 months or so to run 3 motors at about 1.5 amps each with chopper driver boards. This is not a regulated power supply but it works great for chopper boards since the current is regulated by the chopper anyway.

What does your wiring diagram look like? Also, will CAT 5 wire be heavy enough for the motor connections?

Here is a photo. Normally the negative battery cable is connected to the center tap on the secondary winding of the transformer and each end of the secondary goes through a diode to the the positive battery cable. By simply going straight from each end of the secondary (see gator clips in photo) to a full wave bridge rectifier you can increase the voltage since you are using the entire winding all the time instead of just half at a time like in the original configuration.

I made a simple power panel to hold all the components together. I have a couple of 4700 uF capacitors between the + and - output of the recifier to smooth out the power. I also have 4 fuse protected outputs for 4 motors (only 3 pictured). Each has a diode across the fuse to prevent back EMF if a fuse blows (I learned about this the hard way).

With this setup I can get the following voltages under load:

With the original setup on the charger:
Switch setting on charger Voltage
6V/6A 7V
12V/2A 10.1V
12V/6A 11.9V

With the rewired setup:
Switch setting on charger Voltage
6V/6A 15.8V
12V/2A 26.3V
12V/6A 32.2V

I have been running 3 motors at 1.5 amps per phase so that would be anywhere from 4.5 to 9 amps depending on exactly where the motors are. I usually use the 26.3V setting but I haven't had any problems with the 32.2V setting. I plan on adding 1 more motor but I need to build a new driver board first.

Wal-Mart (Schumacher brand) battery chargers are awesome. I use them for everything from anodizing aluminum to building TIG welders to CNC power supplies to (can you imagine) charging batteries. They are very versatile and relatively cheap at approx $25 apiece. Harbor Freight sells a very similar one that you can sometimes get for about $20.

Anyway, I hope this helps.

Oh yeah, the Cat 5 wire question. I'm not sure what size Cat 5 is. I usually use 18 to 24 gauge for the motors with no problems. 4 conductor 24 gauge telephone wire seems to work fine for 1.5 amps.

That's Cap. I'll have to look into this some more. Are you using bipolar motors or Unipolar, and where do you buy them?

Bipolar motors. The 2 x axis motors are 142 oz*in Pacific Scientific motors I bought off ebay. The y axis motors are Applied Motion 60 oz*in motors I bought from www.alltronics.com. They are item number 25M002. In hindsight, the Applied Motion motors would have probably worked fine all around.

WHat are you driving with these motors and what driver are you using?

i used a power supply i got off ebay, some sort of photocopier power supply actually, but in its own metal case, made to go inside a machine, not terribly pretty or user friendly but it was only 25 bucks and its lasted 2 years now. it was a 24v 6.5 a. I remember having to choose between several that were for sale. Im surprised there arent more to be found now.

Thanks Erase - I found a schematic for one that has 12v, 2.2 amp transformer, going through a triac (400v 8 amp) a few resitors and a capacitor. The guy uses it on 24" and 48" bow for cutting wings. I hope it'll power a longer wire but I'll have to wait and see. I want to use an 8' cutting wire.

WHat are you driving with these motors and what driver are you using?

I'm driving 3 of the 4 motors on my CNC hotwire. 2 of them are 142 oz*in Pacific Scientific motors on the x axis and the 2 y motors are 60 oz*in Applied Motion. The motor drivers are all homebrew half stepping bipolar boards with current chopping. I'm only running 3 of them with the power supply because I've only built 3 drivers that have choppers on them. The 4th motor is driven with an earlier driver prototype that doesn't have current chopping on it. I intend to replace it with one that does but everything is working fine right now and I'm spending my time cutting foam instead.

I'm driving 3 of the 4 motors on my CNC hotwire. 2 of them are 142 oz*in Pacific Scientific motors on the x axis and the 2 y motors are 60 oz*in Applied Motion. The motor drivers are all homebrew half stepping bipolar boards with current chopping. I'm only running 3 of them with the power supply because I've only built 3 drivers that have choppers on them. The 4th motor is driven with an earlier driver prototype that doesn't have current chopping on it. I intend to replace it with one that does but everything is working fine right now and I'm spending my time cutting foam instead.

Well, I'm just getting started, so I have to ask a lot of questions. The 4 motors I have are 98 oz, unipolar and on the next machine I'm thinking about servo motors. Where did you buy the 142 oz motors?

I bought them from ebay (don't remember where exactly) for $20 apiece. To tell you the truth, I'm much more impressed with the 60 oz*in motors that I bought for $7.95 apiece from Alltronics.They have 6 wires so you can wire them unipolar or bipolar. Under the conditions I've been using them, they actually feel stronger than the 142 oz*in motors. Probably because I'm running them at 1.5 amps which is closer to their max rating of 2.3 than the "larger" motors which max out at 2.8. I could increase the current but I'm not having any problems with any of them and more current just equals more heat to have to cool on my driver boards.