Re. Started winding today (rolled cap poly thickness)

>Original Poster: Esondrmn-at-aol-dot-com 
>I have built two rolled poly caps and lost them both due to overvoltage.
>I also used only one layer of .062 poly originally.  Two .030 layers
>would be much better and three .020 layers would be even better.  In my
>opinion .062 poly is only good up to about 9 or 10 kv and will fail at 12
>kv.  I think three layers of .030 for .090 total is good up to 12 kv
>(talking ac, rms here) and I think you need either four layers of .030
>for 15 kv or perhaps six or more layers adding up to .090 total.
>What experience have others had in this area?
>Ed Sonderman

I too have built and lost two rolled poly caps, both with 15KV NST's.
#1 was built with two layers of .04" poly, immersed in mineral oil but
not vacuum pumped prior.  It lasted a few dozen 30 second runs.

#2 was built as two series units, each using one layer of .04" poly.
This one was vacuum pumped prior to mineral oil backfilling.  One of
these units failed after a 7 minute continuous run due to corona heating
at the edges of the foil.  Complete details on my web page:

Regards, Gary Lau
Waltham, MA USA