Re: Czpacitor Question- Repost

[Terry Fritz <twftesla-at-xxxxxxxxxx>]

Hi Ronn,

	One of the best things about MMCs is that you can take a bunch of caps and
do all kinds of destructive testing on them without a second thought.  Not
so easy to do with a cherished homemade capacitor.  I think two things kill
caps, voltage and current as a function of time.  Voltage is the first and
easiest thing to check.  Carefully noting resonant rise effects, run the
cap with 22kV (peak) at 60 HZ (no gap or anything) and let it cook for a
few hours straight.  That will verify that the voltage standoff and basic
construction is sound.  If you cap is 10nF.  You might be able to play with
it so as to run 60mA RMS though it too but that is a far cry from the 10
amps RMS it should run at.  So, you need to hook it to a primary with no
secondary in place and let it rip in a primary spark gap circuit.  You are
looking for heating and failure.  Run it for a short time at first and
check it over (discharge it first ;-)) for problems and then be more
aggressive.  If you can't blow it up with the voltage or the bare primary
circuit test, you can pretty much call it good.  The "number" of spark gaps
is not an issue.  You just need a gap that will last longer than the cap ;-)

I would definitely have a protection circuit for the NST!  Also, be careful
of fire and other disastrous things happening.  Just be ready to handle a
failure especially if it is oil filled.  Safety glasses and all that stuff
should be used and have the off switch and fire extinguisher handy as well
as a direction to run in if it goes really bad...

Cheers,

	Terry



At 12:39 PM 11/28/2000 -0500, you wrote:
>Hi Terry and fellow coilers,
>
>This question is for all you 'seasoned coilers' out there. I have a new idea
>for a rolled poly cap, and I wanted to test it to destruction to see if my
>calculations for rating are correct and to see how much abuse it would take.
>The question is: What would be the best way to set up a circuit to test this
>cap using a 15/60 transformer?  I plan on using a variac to control power
>and a HV probe to monitor input to the cap. How many spark gaps should I
>use? I assume some sort of protection filter circuit would be in order to
>save the transformer. 
>Thank you for your help.
>
>Ronn
>(Teslamanian Devil)
>