/diy/ - Do It Yourself

>>1665374
>If it's 30V it would need about to 5A to be 135W. I'm sorry I don't have more info on this, but I believe they are saying the resistor is rated for 135W and at 30V and 15 ohm, it would be dissipating 60W, well within its rating. The thing that doesn't make sense is that as you bring the brush up the resistor to the +30V end, the resistance drops as low as 2 ohms which seems like it should be frying the resistor if it's only rated for 135W.
>What kind of load
I guess I'm not sure, somehow the voltage and current coming out of the variable resistor are going into one set of windings in a transformer and varying the output current of the other side of the transformer. Pic related if it means anything to you. I know this says 24V on the supply to the variable resistor but I'm pretty sure mine is reading high 29's, I will check later.
>>1665381
Yes it is for a welder. 220V 1PH 72A AC in, 300A 32V DC or AC out.
Full wiring diagram attached
> transistors deal in dc only
> if you PWM
This would only be replacing the DC variable resistor that's controlling the output of the transformer that's actually putting out the welding current. I'm not sure yet how it's doing this, but it's a definitely a DC only control circuit on the welder that I'm trying to emulate.
That said your point about semiconductor caveats is concerning, this thing has an AC spark gap high frequency generator to start the arc, and beings it's a >300A transformer, they recommend to have any electrical cables, including lights, shielded with a ground rod every 10' if they are within 50' of the welder.
Thank you both for your knowledgeable and encouraging replies.