Re: [TCML] 942 destructive high voltage test

[Bert Hickman <bert.hickman@xxxxxxxxxx>]

Hi Mark,

That's great information! The capacitor initial DC breakdown voltage of 
about 4500 VDC appears to be fairly consistent across the sample. 
Assuming ~100% voltage reversals (%VR) in TC use, this suggests that the 
caps may withstand 2kV of RF (4 kV peak-to-peak) as long as they are 
operated below their RMS current limit (about 8A).

As Jim mentioned, overvolting (including %VR) has a dramatic impact on 
lifetime. Maxwell uses the following formula to estimate lifetime a 
elevated voltage versus rated voltage:

Life at V2 =(Life at V1)*(V1/V2)^n

While the historical value for the exponent (n) is about 7 for 
polyester, it is about _15_ for polypropylene! Although catastrophic 
failures in MMC caps are usually prevented by self-healing, continued 
overvolting and faulting/clearing will rapidly convert your cap's 
metalization system to Swiss cheese.

Bert
--
Bert Hickman
Stoneridge Engineering
http://www.capturedlightning.com
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Mark X2 wrote:
> A little while ago I posted to find out if anyone did some recent testing
> on the 942 caps.
>
> There was no response, so I decided to sacrifice 5 of my 942s for the
> cause.
> (In the mean time I found that Terry Fritz tested one of these caps back in
> 2001
> http://www.tb3.com/tesla/capacitors/GeekCaps.htm)
>
> Each cap was hooked up to the output of a BAUR PGK 25 High Voltage Test Set
> to measure the leakage current while increasing the (dc) voltage until they
> finally started to fail internally or blew up.
>
> Anyone who's interested in the results: 942 cap
> test<https://www.dropbox.com/s/qjcuskwabhhrsat/942%20Cap%20test.pdf>
> I'd like to invite you to draw your own conclusions and to discuss them
> here.
>
> Mark
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla



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