drsstc - catastrophic failure!

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Original poster: "jimmy hynes by way of Terry Fritz <teslalist-at-qwest-dot-net>" <chunkyboy86-at-yahoo-dot-com>


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A few days ago I had it running at 280 volts, pulsing the primary coil and 
capacitors for 2 cycles (400 amps peak) every second. But now it is dead.

I was running it with 150 ohms in series with the ac hot, and it was 
working fine up to around 280 volts. At around 280 volts, the 
microcontroller started freaking out every few pulses and sometimes shut 
off. I am almost certain it picked up noise from the primary coil a few 
inches away. I then looked at the power line to the micro. It was all over 
the place from 0 to six volts, following the 60khz current in the 
primary.  I had forgotten to add a decoupling capacitor. That was stupid, 
as it could have saved my project. I will put some fat ones on before 
running it again ;-).

I was just about to turn the thing off, when I heard a loud pop, and the 
dog ran into the bedroom to hide under the table  After I turned it off, I 
looked over and saw smoke.  If the capacitor bank was at 280 volts, there 
were  88 joules in there. The pop killed seven out of the eight IGBTs that 
I was using! These things are tough, but not indestructable.  I can find 
ways to break anything ;-). The IGBTs are all in one piece but every pin is 
shorted together. I think that happens when they are over-volted. My guess 
is that the microcontroller got confused and told all of the IGBTs to go on 
at the same time (I have no shoot through protection).

I might try some brick IGBTs, because my assembly was pretty much 
destroyed, only the diodes are  left on the heatsink. There are some on 
ebay now that look fast enough, so I might snatch them. I am also trying to 
contact Powerex about their complete Pow-R-Pak modules. I want to finish 
this thing!

I've also gotten advice from Bill Reass, who designed a resonant pulse 
transformer for physics research at Livermore Labs.

<http://arxiv-dot-org/ftp/physics/papers/0008/0008125.pdf>http://arxiv-dot-org/ftp/physics/papers/0008/0008125.pdf

I want dibs on his power supply when they scrap it out :-). They're pulling 
10MWatts peak and 1MWatt average power!






Jimmy



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