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Re: Advice needed on capacitor tests
In a message dated 4/2/99 3:39:59 AM Mountain Standard Time, tesla-at-pupman-dot-com
writes:
>
> This cap took me two days to build and I don't want to go through it all
> again!
>
> Any help would be deeply appreciated.
>
> Alex Crow
>
Alex,
It sounds to me like you have punctured the dielectric in your cap(s).
The hissing is the sound made by the currrent passing between the plates. I
tested some dielectric materials to failure once to see just how much they
could take and heard the hissing noise you spoke of on failure. The lack of
a spark across the gap would tend to support this. You should have placed
them in oil before use and vacuumed the air out before ever using them(the
corona helps to break down the poly). You should also have somewhere for the
energy to go(like a tesla coil eg.). All that energy has to go somewhere
and you only gave it the resistance of the spark gap to dissapate that
energy. When you opened that gap up, you also placed a very high voltage
stress on the caps which lead to the failure of at least one of them. You
are lucky the transformer secondary didn't go up in smoke too. The energy
that was not dissapated in the gap would be sent back into the secondary and
since you matched the impedance(for 60 Hz) as many do, you experienced a
resonant rise in voltage which is why you got such big sparks at the low
input voltage before the cap failure.
Mike