Ive been using one of those 53uF 3500V caps for about 25 years at 2500V no
load and it barely feels above ambient after being on for many hours. Its a
good cap for a couple of 3CX800's, 813's, loafing 3-500Z's or similar tubes
Ive heard about and seen the results of one letting loose when run at close
to 3500V. The problem is a high ESR that cant handle the ripple current of a
HV PS, especially a doubler.
OTOH Ive been running a 4KV real oil cap with yummy PCB's at 3900V in the 2M
amp for about the same length of time and it stays at ambient.
Carl
KM1H
----- Original Message -----
From: "Steve Thompson" <g8gsq72@gmail.com>
To: <amps@contesting.com>
Sent: Monday, June 20, 2011 2:51 AM
Subject: Re: [Amps] Using an oil capacitor
>> I have been following this thread with some concern. My oil filled
>> capacitor measures
>> 4 3/4" X 4 1/2" X 9 1/4", its markings are as follows. General Electric,
>> Capacitor, Made in U.S.A.,
>> 25F492, 25uf at 4000 VDC. How can one tell if this capacitor is suitable
>> for a HV power supply.
>
> It can be very hard to tell - if it was designed for low duty
> pulse discharge the designer could concentrate on size, weight and
> price without worrying much about getting heat out from the
> inside. In a PSU heat generation is more sustained and it could
> end up cooking on the inside before you notice it's getting hot on
> the outside. Some people have similar caps which have run for
> years, others have them fail in a few months.
>
> If you decide to use it, I'd suggest fusing the transformer
> secondary so things are protected if the cap goes short.
>
> Steve
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