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Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]

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Refrigerator:
Hooked up my scope to the gate of one of the low side MOSFETs to capture the waveform during oscillation.
I also made a quick and dirty current clamp with an inductor core and a clothespin, with 100 turns and a 100Ω resistor it should give me 1mV/1mA.
Yellow - gate voltage, Red - transformer current.
Any idea where this could be coming from? Connecting a 23.5Ω load on the output stops the oscillation.

magic:
I would guess the PWM controller just drives it that way. :-//

Refrigerator:
I decided that the 23Ω load resistor is an ok fix and ran some tests at full voltage.
For these tests i made a 2Ω load resistor out of some old welding wire, but 2Ω was a bit much so i stepped it down to 1Ω and later ~0.75Ω for my tests.
Checked the voltage range and it goes from 18V to 25V, testing was done at 25V with the aforementioned resistances.
I let the welder do its thing for about 15 minutes and checked the temps. Both heatsinks were warm, could say almost hot but not bad, considering there was no fan plugged in, that's with the 1Ω load.
Too bad i don't have a temp probe so i can only go by feel. Of course i unplug and discharge everything before i go poking my fingers inside.
Before i do any more testing i'll go make a temperature controlled PWM speed controller for the fan i'll be using because it uses a PWM input and is very loud at full power (afc1212de).


Edit: had to downsize the image.

Refrigerator:

--- Quote from: magic on August 16, 2019, 02:18:32 pm ---I would guess the PWM controller just drives it that way. :-//

--- End quote ---
When the trigger is released the GDT drive transistors are turned off along with the controller output (DTC pulled high) so it's not the controller.
I guess it was because there was no current going through the GDT that allowed the oscillation, anyways it's fixed now.

Refrigerator:
I think it's ready for a true weld test, but i'll do that tomorrow, because it's dark already and all the mosquitoes have come out to bite me in the arse.
It's quite amazing what a little airflow can do, with the fan barely idling the MOSFET heatsink is only lukewarm and the diode heatsink is ice cold when running just shy of 700W.
I also "accidentally" melted the load resistor i made.  >:D When i shorted the melted ends out i got some hissing arcs.
One thing i'm not feeling too confident about was the squeal coming from the inverter during moderate loads (above 1kW).
Last time right before it blew up it started squealing, which is why it worries me so much.

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