[TCML] SISG Damage Report

[FIFTYGUY@xxxxxxx]

Folks-
 
    Finally, I've got some useful info!
 
    Today I repaired the SISG4 board I blew up in my  last run. I thought I 
only had one bad module, but when I looked closely, I  realized that I'd blown 
two on the same board. Amazing how the coil keeps  running fine when the 
circuit boards are on fire! Try that with your  DRSSTC...
 
    The important thing is, this board had the 2nd and  3rd modules 
(sections) that I'd blown up. Here's the damage report from all the  bad sections so 
far:
 
    1st blown section I had posted about earlier. I  believed at the time 
that it suffered a direct secondary strike to the SISG4  board. This section had 
all 3 SIDACs failed, 1 blown wide open, the other 2 with  their cases cracked. 
In fact the blown one arced so bad, it welded its lead into  the copper board 
trace.The 24V TVS failed with its case visibly cracked. The  IGBT looked 
fine, but it was a dead short to all three leads.
 
    The 2nd blown section also had all three SIDACs  failed, 1 with a cracked 
open case, the other 2 looked fine but were dead  shorts. Again the 24V TVS 
failed (even though it looked OK). And again the IGBT  failed, even though it 
looked fine.
 
    Now for the good part:
 
    The 3rd blown section again had all 3 SIDACs  failed. Again, one blew up 
so violently the fiberglass board material was  cratered and the traces 
completely vaporized. Carbon coating everything nearby.  The other 2 SIDACs look OK 
but were again dead shorts.
    The 24V TVS is fine!
    The IGBT is fine!
 
    In all 3 cases, the 33V TVS's were OK. And all the  little 40V Schottky 
Diodes were OK. As far as I can tell all the .1 uF caps were  OK, too. But I 
replaced all the semi's and caps anyhow (cheap insurance). I'm  keeping the good 
IGBT, though!
 
    All this leads me to believe that the SIDACs are  the weak link. 
Obviously they failed in the 3rd module, but the IGBT is still  fine. I know the IGBTs 
are getting mighty hot with the abuse I've been giving  them. But I'm 
thinking of gluing on heatsinks to the SIDACs to help them out. 
 
    What do you electronics guys think? 
 
    In other news, maybe we'll be using Silicon Carbide  transistors in our 
TC's one day:
 
_http://powerelectronics.com/power_semiconductors/transic-competes-with-igbt-0
514/_ (http://powerel
ectronics.com/power_semiconductors/transic-competes-with-igbt-0514/) 
 
-Phil LaBudde
Center for the Advanced Study of Ballistic  Improbabilities



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