Re: [TCML] SISG Damage Report

[FIFTYGUY@xxxxxxx]

In a message dated 5/17/08 6:39:30 P.M. Eastern Daylight Time,  
bartb@xxxxxxxxxxxxxxxx writes:

 
>If you do heatsink the Sidac's, I expect you'll tie all 3 Sidac's  
>together at each module?
 
    No, definitely not! Keep them all electrically  isolated in every way! 
I'm thinking of gluing a little solid piece  of aluminum to each one. I didn't 
see any off-the-shelf heatsinks that  would lend themselves well to the 
packages and spacing requirements.Even then,  they could be physically mounted to the 
same heatsink, so long as they were  electrically isolated from each other.
 
>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).  

>From the way Terry tied SIDAC tabs together with  brass screws to short them 
out (for Piranha II tests), it would appear the  tabs are definitely 
electrically hot and tied to one of the leads.
 
>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.



Of course.

>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.
 
    The first section that went was on the outside  edge of the coil, in a 
very susceptible area. So I felt pretty sure it was a  secondary strike. 
 
    The other two sections happened during a later  run, after I had put up 
steel shielding around the bottom of the coil. One of  the blown sections was 
on the *inside* of the underside of the coil, where it  was least likely to 
take a secondary strike.
    Or who knows? Maybe those streamer-to-primary  strikes aren't harmless 
after all. The thing takes a lickin' and keeps on  tickin'. Maybe the loss of a 
section carries a disproportionate increase in  breakrate that keeps the 
streamer behavior relatively constant? But it might  "avalanche" where the faster 
breakrate increases the thermal load to the  remaining operating sections...
 
> I'm curious, are they getting hot!


I'm curious, too, but I'm not getting anywhere  near the thing at full power 
(not even close enough for an IR thermometer. I  guess I'd have to set one up 
in a shielded jig near the coil, and read it from  a safe distance. Or have a 
*really* well-isolated RTD glued to the things.Or  maybe a thermal imager 
would suffice (if you were crazy enough to bring one  close to a TC!).
 
-Phil LaBudde




Center for the Advanced Study of Ballistic  Improbabilities



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