[Prev][Next][Index][Thread]

Advice needed on capacitor tests



Dear All,

I finished my first layered cap today, and decided to give it a test
run. I had oiled all the plates as I built it, and given it a quick duck
in a bath, but the testing was done 'dry' so to speak. I hooked the
thing to a variac and gapped the terminations about 1/4 inch apart for
safety. I turned up the voltage on the variac, and got really loud
sparks across the termination leads at only 20 volts in!

Then I increased the gap to nearly half an inch, and got huge,,
deafening bangs at just about 32 volts input to my neon, which I worked
out was only just over 1300V on the output! I then gapped further, and
just past 35 volts in the gentle hiss from the cap lowered in pitch very
suddenly and got a lot louder - and no more sparks on the output.
I bumped up quickly to 45V in and still no spark, but the hum stayed the
same.

To put it bluntly, this worries me. I have layered my plates with an
inch of gap on all sides - I was hoping this will be enough with 2 caps
in series across my 10kV NST. I have heard that others have been fine at
15kV with 1.5 inches of minumum inter-plate distance at the edges. But
if I can only get up to a fifth of the voltage on the input at most in
this 'damp' state (admittedly there are air gaps at the edges) can I
expect them to take 5kV each when they are fully flooded with oil? Is
this just a case of me being premature and should I wait until I have
run them in in my deep-fat bath before I get too worried? i know this
sounds like corona discharge drawing extra current from the transformer
and thus limiting the output, but will my corona be five times less
severe when there's no air left in the thing? Maybe it's doing resonant
charging (0.04uF on a 10kV, 150ma short-circuit current neon) and I'm
getting a serious voltage rise)?

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