Re: Capacitor voltage - AC or DC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Matt,

At 09:10 PM 8/27/2005, you wrote:
> In a message dated 8/27/05 10:41:58 P.M. Eastern Daylight Time, 
> tesla@xxxxxxxxxx writes:
> Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
> Hi,
> Somehow, someday, somebody, has to do something... :-))
> Probably the "last unknown" of MMCs is how long the (CD 942C20P15K)
> will tolerate say 60Hz at 6000Vp-p....
> Maybe do a bunch of different voltages to make a nice graph of
> 'lifetime vs. over voltage'...
> That would tell us all we still want to know...
> Cheers,
>          Terry
>
>
> Hi Terry,All,
>
>    To get a meaningful number, we would need to look at the 
> distribution of lifespans of, say, 6 to 10 caps at each voltage. 
> This would also result in some QC data for the "identical" caps. 
> Soon as I free up ~$200 I will be happy to kill some some caps for 
> science. My gut feeling is that higher voltage = both shorter lives 
> AND narrower distribution of lifetimes. It will be fun to find out. 
> Thirty caps at each voltage would provide really statistically 
> significant numbers. Maybe 3 people testing 10 caps at each 
> voltage, or 5 people testing 6 at each voltage?
>
> Matt D.

I don't think the statistical distribution between caps is very 
great.  Probably "three" is fine to detect a distribution 
error...  We could "go back and look" If there seemed to be a 
problem...  If the cap failures are an "hour, week, and then a 
month"...  Then we are all out of whack...  But if the failures are 
at say 78 hours, 82 hours, 81 hours....  Close enough ;-))  One could 
take the distribution of just three cap failures and find the error 
limits!!!  If the failures are "close", no problem ;-))

But probably a pretty plain "wear out" of the dielectric due to ion 
damage...  Don't make me go "weibull" ;-))

The real problem is having a "cool place" where say a CD cap is 
across a NST on a variac and the cap goes ballistic in big flames... 
I just don't have a fire proof, no burning the house down, "place" to 
do the testing...

"I" could supply the "materials" to a dedicated trusty tester 
;-))))  Probably three caps across a MOT on a variac with a timer thing...

Cheers,

        Terry