[js530]

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]

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]

Do you have a wiring schematic for this. I bet I could scrounge up most of this.

[siciunas]

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]

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 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]

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

[Hamadamj]

Very interesting !

[sanddrag]

I'd like to see a bead you've layed with it.

[js530]

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]

Wheres the thread on your DIY Plasma Cutter?

[slappynuts]

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]

Here is the answer to all of your questions.

http://www.geocities.com/CapeCanaver.../simpleign.htm

[iEdd]

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. (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]

Yep. (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]

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/k..._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).

[js530]

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]

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

[toolmanx]

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

[js530]

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]

Great work. Its certainly coming together.