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Gizmo

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Joined: 05/06/2004
Location: Australia
Posts: 5167

Posted: 11:29pm 20 Dec 2025

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Hiya

I have a old AC welder and plan to use this as a power source for my TIG welding. Currently I use a cheap inverter welder, but I cant switch that on or off with a foot switch ( I have a contactor I can switch on and off with a foot switch ).

I also want to try TIGing aluminum, so need AC from time to time.

This old welder is a adjusted by a crank at the top, to move the primary coil inside the transformer. It works OK, though draws about 150 watts at idle.

The TIG part is a HF spark generator that is connected in series with the lead to the welding torch. Its operated by a button on the torch handle.

So, I need to add a rectifier to my welder. I have a pair of 100Amp bridges on a heatsink for that. Now I have questions about the bypass / suppression capacitors I should be using. The TIG box adds energetic HF spikes to the circuit that will kill the rectifier in the welder. So I'll need a add capacitors across the welders ( new ) DC terminals to stop this spike getting to the rectifier, and I believe I should be adding caps to the mains input to stop spikes getting into my mains supply.

Any suggestions to what value and type of capacitors I should be using for this?

Glenn

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Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 604

Posted: 08:31pm 21 Dec 2025

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That sounds like an interesting project Glenn.
I have a combination welder but it is only DC so aluminium welding is out as far as i have heard.
I mainly use MIG and Stick welding as i don't have a TIG torch yet.
I know that in the past I have heard of high frequency pulses being used for welding but I did not know that Tig welders needed that too.
Is the high frequency part on the Tig welding section only used to strike the arc?
Sorry I don't know about the capacitor sizes you need, I am guessing that they need to be designed to soak up the high frequency so would need to be sized to suit the actual frequency of the pulses but that is out of my level of knowledge.
Good luck
Pete

johansen
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Joined: 01/08/2014
Location: United States
Posts: 10

Posted: 12:03am 22 Dec 2025

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You only need something on the order of 1 to 10uf on the rectifier to bypass the high frequency ac to start the arc. Any common film cap will work. I would use something rated at least 400 volts. The welder may only output 70vac max but the leakage inductance on the secondary can generate a lot more when the arc breaks or stops. 10uf is probably enough to absorb it.

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