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Re: Specs for used eBay Maxwell capacitors



Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>



>>From: "Tesla list" <tesla-at-pupman-dot-com>
>>To: <tesla-at-pupman-dot-com>
>>Sent: Wednesday, February 26, 2003 7:14 AM
>>Subject: RE: HV Capacitors - Good stuff for sale
>I have been using the 31XXX series Maxwells for over 3 yrs now and they 
>still are holding up... ( hmmm   now watch... I'll burn them up since I 
>talked about them)   at present I have 4 in series for 200KV total -at- 
>.1mf   being pushed by  34KV+ .
>
>they have seen many hours of use ( 3 haunted house applications and at 
>least 3 hrs per month elsewise..)   hmmmm lets see...
>
>2X  (6 nites a week for 4 weeks 5 hrs a nite ) -at- 50% duty cycle  + 4 nites 
>-at- 50% duty cycle ( 5 hrs a nite)   + 3 hrs a month for 33 months = 133 hrs
>
>133X 60 = 7980 minutes      X 60 =  478800 seconds    X 54KHZ  = 25.8 
>billion pulses      or to consider just the primary charge pulses...
>28.7 million ...
>
>Id say they are handling things well  ;)

Aha... you have been operating these things derated.. The life is a 
function of many things... voltage reversal and applied voltage being the 
notable ones.  http://home.earthlink-dot-net/~jimlux/hv/caplife.htm has a 
description of the equations, oddly enough, for Maxwell caps (polypropylene 
dielectric, which is what's relevant..the exponents change for other 
dielectric systems)

Most important for life is the voltage, since the life goes as the 7.5 power!..

If you're putting in 34kV, and the string is rated at 200 kV, you should be 
getting 5.9^7.5 life out of it..that's about 600,000...

If it was rated at, say, 100,000 shots before, now it's rated at 
600*100*1E6 or 6E10 shots..
60 billion... You're probably running a pretty high voltage reversal, and 
the typical rating for low rep rate caps is 10%.. but, that's only a 1.6 
power (for Q..)...
Say you've got a Q of 10 instead of the rated value (assume 1 for the rated 
value)..

OK, now you're down to about 15 billion shots... a long, long way from 30 
million...

Moral of the story.. run lower than rated voltage and get long, long life...