Re: Why do my caps keep blowing?

When you connect the transformer and the capacitor up together
with no primary and no secondary, then you will experience the
full effects of what we call RESONANT RISE. With a 12KV 
transformer you can easily be creating a resonant rose of 60KV 
or more. This is probably what is killing your capacitor...
you are lucky it didn't take out your transformer, too!

I have been able to get over 100KV of resonant rise from a 
12KV transformer. At that point there were nasty white arcs
snaking across the entire surface of the HV insulators!

Always test with a spark gap, safety gap, primary and
secondary system in place!

Fr. Tom McGahee

> > Date: Tuesday, January 26, 1999 5:01 AM
> > 
> > Original Poster: "David Hosking" <davidhosking-at-bigpond-dot-com> 
> > 
> > 
> > Hi all,
> > I am making my first tesla coil and am having trouble with caps blowing
> up.
> > I am making them from 1mm thick poly (10layers of 100um) 
> > They are vacuumed & filled with fresh transformer oil.
> > When I place 12kv30ma a.c. across them (0.008uf)  with no load to test
> them
> > they puncture through the middle of the poly within 5 minutes.
> > Perhaps I shouldn't test them like this? 
> > I clean everything with alcohol and wearing rubber gloves during assembly
> > then vacuum them for 4 days.