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Registered Member #75
Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711
This goes into chatting since I don't have much of a clue what I am talking about. I have never dissected a welder, but I imagine there is not much but a IGBT bridge, a fat ferrite transformer and some kind of PWM circuitry, basically an ATX supply on steroids. Welding would sure be fun so this seems to be something that should be tried out. I wonder if anyone beat me to it, otherwise I might try modifying my small induction heater for welding.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
There are two different types of TIG welder: DC and AC. The DC type is just a switched mode power supply, like you say, that puts out around 30V open circuit and around 100A short circuit, with roughly constant power limiting in between.
The AC type follows that mess up with a H-bridge inverter to chop the DC output back into a low frequency square wave. The frequency is sometimes adjustable between about 50 and 500Hz, and I believe the duty cycle (positive vs. negative) is too. In practice, I don't know whether these stages are separate, or whether the inverter is part of a synchronous rectifier.
There is also often a HF assist circuit, similar to a Tesla coil, that superimposes a high voltage RF signal on the welding electrode, to help start the arc and keep it going. Cheaper TIGs don't have this and are known as "scratch start".
The DC type will weld steel only. If you want to weld aluminium, you need the AC unit, and a lot more skill. AC welders tend to be bigger and more powerful, since aluminium takes more current to weld than steel. The last guy I saw welding aluminium was using one of the old fashioned TIG welders based around a large 50Hz transformer and saturable reactor, with a real spark-gap Tesla coil for HF assist. It was about the size of a washing machine, needed three-phase service and water cooling, and put out 300A.
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Homebrew TIG welder?
