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After slight snubber circuit modifications (more below), I was able to test my bridge under full welding power of 199 amps.
I also added a cooling fan to cool the main heatsink with IGBTs, as well as a heatsink for the big ass diode in the snubber circuit. I drilled a hole in that second heatsink and tapped it for 3/8-20 NF thread, and screwed the diode in.
It is cold in my garage, perhaps 35F. Given that, and the fan action, all parts of the bridge stayed cool, except for the main heatsink, which became warm. Under full power, the IGBTs are expected to produce approximately 1.2 kW of heat.
Snubber modifications: I added a little Christmas tree of 150 V rated varistors (total of 5 now), as well as a small 0.33 uF capacitor across the DC rail. I also remounted the snubber diode by drilling a tapping a heatsink that I had, and screwing the diode in.
The test (among many tests at smaller amps) went on for a couple of minutes, until the breakers blew. Like I said, nothing warmed up.
