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Re: [TCML] SISG Damage Report

Hi Phil,
If you do heatsink the Sidac's, I expect you'll tie all 3 Sidac's together at each module? I would be interested if that causes any problems. I don't expect it to as the tab (pin 2) is not tied to anything on the board, but not sure if tying pin 2 to the other Sidac's would cause any changes in switching (I'm not sure where it's tied internally and the data sheet simply says not to use pin 2). But if the Sidac's are getting hot, then it makes sense to sink them. However, if it's simply due to a strike and the Sidac's are remaining cool, then sinking the Sidac's won't help.
Something that has confused me a little here is that you think the boards took direct strikes. If that's the case, the Sidac's aren't really the problem. They are however the sharpest point on the board and are probably likely to be hit by a strike if allowed. I'm curious, are they getting hot! 

Take care,
Bart

FIFTYGUY@xxxxxxx wrote:

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
**************Wondering what's for Dinner Tonight? Get new twists on family favorites at AOL Food. (http://food.aol.com/dinner-tonight?NCID=aolfod00030000000001) 
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