slappynuts

Ok well I have one transformer rewound and I measured out the output voltage at 12v. I was kinda hoping for 20 so I guess I messed up on the counting when I unwound the secondaries. If I hook up the other one in a series I should be able to get enough voltage out. Now for 120v@20a and two transformers I should end up with 24v@ about 100amps ac.

stealthiskey

Lookin good. I built an AC stick welder from two rewound microwave transformers. It worked pretty well, been thinking about taking a shot at a tig. Just be careful with the current on that high voltage. What do you have in mind for pulsing/reversing the output?

babowc

upddddddddddaaaate!

WTF

is this chuc from BF ? well i have to say your smarter then you look if it is

icecubetray

If you want to get real fancy......this one is pretty sweet....

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

Aaron Cake

What you are making could very well kill you.

There is going to be a LOT of 60Hz on the output of that ignition coil. The lamp dimmer and capacitors for a very basic oscillator, but it is very dirty as well. Having 60Hz at the output will negate the skin effect of typical high frequency high voltage AC and could kill you if you come into contact with the output of the torch.

I would highly recommend ditching the lamp dimmer circuit and using a proper high frequency oscillator. Here's an example:
http://www.aaroncake.net/circuits/hvgen.asp

Even that is a poor example as the frequency can vary a lot with load. A better circuit is based on the 555 timer. You can find them with a Google search for "solid state tesla coil 555 timer".

slappynuts

I have built the 555 timer circuit before and it works fine until you shut it down. The coil would kick back and fry the transistor and your done. not ideal . The high frequency from the light dimmer should do just fine for this set up but before anyone build this I want to test it a little more. As far as it being dangerous,its basically mimicing the voltage and frequency in any tig machine and if your concerned you should be welding

I do think the 555 timer circuit and a bosch ignition module would be a better choice and I will be very quick to switch if I run into any problems with this set up.

Thanks for the quality input. What are your thoughts on my plan for the ginormous SCR on the power feed to the transformer? I am probably going to use the 555 timer on this circuit because the because the big *** caps are kinda hard to come by and the 555 parts are available at any radio shack.

mosheen

If you're frying transistors, you need to put a diode across it in reverse bias. It wont conduct while the circuit is running because it's backwards, but it will shunt the fly-back from the coil once you switch it off. It's a common technique for relays, solenoids, etc. That's assuming you're using DC in that part of the circuit.

Smith-02

did you electrocute yourself yet?

slappynuts

I thought about that but I think if we use a ignition module from bosch it will be more reliable. Its made to be used with that coil and can be found on any european vehicle form early 80 till late 90s. The other problem is if you use the 555 timer you need a power supply. Its not a problem because you will probably need one for other 555 timer circuits in the machine. The main goal was to keep the parts list down but I guess computer power supplies are cheap and more than capable.