SISG failure report

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

I got a chance to look at the SISG we used for the ball lightning / 
plasma ball test.  As expected (now :o)) the 875 joules just melted 
the IGBTs down and everything was a dead short on all their 
leads.  But no outside visible damage at all unlike DRSSTC IGBT failures ;-)

But all the 33V TVSs on the gates were all at ~21V now too!!!  I 
tested a new one and it was fine at 33V.  So they all must have 
gotten equally "cooked" a bit.  Sort of obnoxious since it would 
'not' be an obvious failure if one did not test it carefully.  It is 
hard to blow IGBTs "normally", but one should probably replace the 
gate TVSs too just in case.  I suppose I could use the 1.5kW instead 
of the 600W too.  I guess the gate TVS was a "good idea" ;-)  It 
might have saved the other few gate drive components.  Everything 
else was fine including all the SIDACs.

So I have the 33V TVSs all replaced and I will glue heatsinks to new 
IGBTs and get them put in and right back in business!!  I am now 
pretty sure the only way to kill the SISG in Tesla coil service is 
just by too much RMS current way overheating them which is really 
hard.  Maybe but a giant current pulse into a dead short too.  But 
the thing is darn tough!!!  I would not be too surprised to seeing 
them in the can and coin crusher world rather soon with "giant" 
IGBTs...  the very fast pulse currents there don't heat things much 
and IGBTs like big pulses ;-))  But they would have to be "big 
ones"...  Maybe a good place for giant SCRs there with the SISG 
drivers...  The "silent" can crusher :o))  SCRs might work too for 
the plasma ball thing with some careful inductances added to control 
dI/dT...  When you can "just buy one at Wallmart", that is how they 
will run ;-))

Cheers,

	Terry