So there is some hope for my poor fried critter. I blew another first fet today, had no more spares so I replaced it with a larger type that I did have. So far, the new fet has passed every test. Is this the solution? Well, I still don't have an inverter that works. But, I've connected the HotBox to a variety of loads that I do have and it now handles them as expected, no arcs, no sparks and no blown fets. I don't have enough capacitors to match the inverter load of 2500uF, but I have connected 1500uF and switched it many times, in parallel with a light bulb so I can tell it is working, discharge the cap quickly and get a good inrush too. A friend loaned me a really big capacitor, 8,000uF so I tried that. As Spice predicted, that trips the protection circuit because it can't charge fast enough through 0.5 ohms at more than 200 amps. So that part of the circuit has been tested and passed. And since the large capacitor is almost the same as connecting with a short circuit load, I tried that too. It worked! Red light, no smoke, all good.
Today's fet failure happened while I was using the switch. Possibly the current spike was happening too often for the junction to cool off, losing some SOA. It was working fine during connect and disconnect. But the new fet seems fine with the switch or the sequential connector. I replaced IXFH160N15T2 with IXFK220N17T2. That gave me this possibly important improvement in SOA.
- 220-160-SOA.PNG (33.12 KiB) Viewed 248 times