Capacitors

To: tesla-at-pupman-dot-com
Subject: Capacitors
From: Wesley Brzozowski <brzozoww-at-rchland.vnet.ibm-dot-com>
Date: Thu, 19 Sep 1996 12:55:03 -0400 (EST)

Jim Fosse <jim.fosse-at-bdt-dot-com> wrote: 

> "I wonder if my poly caps are blowing because of small 'points' in 
> their surface? The recommended method of running the caps for weeks to 
> break them in, which I did not do because I had vacuum outgassed them, 
> was to remove the air bubbles. What if it's effect really was really 
> to EDM (electrical discharge machining) off the sharp points that 
> sanding missed or created?" 
>
> After an hour, I could not see any difference in the surface texture 
> under 50 power magnification. 
>
> Has anyone examined or proposed this hypothesis?           

There was a bit of discussion some months back that was similar. Someone  
mentioned mentioned getting failures right at the edge of the foil and I 
suggested the possibility of a voltage gradient problem. I'd also  
hypothesized that those who sanded the edge of heavier aluminum flashing 
to prevent scratches to the plastic might have also created small flakes  
whose sharp edges could cause breakdowns elsewhere in the poly due to an 
increased voltage gradient. The whole thing was very speculative and  
died for lack of data. Perhaps you've come up with a good way to get  
some preliminary data on the matter. 

Wes B.