Blown Cap

Hello fellow coilers,
 well I can say that coiling is a learning expierience. Just yesterday
 I blew my newly
made rolled cap. It was a slight deviation to the standard design we have
all seen, the difference being an extra layer of 20 mil LDPE for a total
of 80 mil. This added thickness, I thougth, would allow me to use it in
service with my 15 KV 120 Ma neon.  Dead wrong! After leting it sit for a
few days and then breaking it in at 7.5 KV, I wired it up to my Resonator
with the full 15 KV and only using 30-40% possible gap distance (point
series with high velocity muffin fan). The first three days no problems (
average run times: 10-40 seconds, a couple around 60 seconds). So I was
getting 36-40" sreamers (not to good for a resonator at that power, but
I'm still working on the design) and then it died! Today I dismantaled the
cap (a messy job) and located a hole the size of my pinky, it was allong
the edge of the flashing threw the plastic. I was very carefull in sanding
and deburring the alluminum and inspected the poly prior to assembly.
  I would like to say that obviously the standard schools of thought do
  not apply in TC
and especially resonator practise. I asumed 600 DC volts/mil breakthrew
voltage and then divided by three for the TC voltage for 16KV. Now
I would sugest dividing the DC breakthrew voltage by four, but would
wonder about that?
 Obvously the way to use homemade rolled caps is to build four and wire
 two in series
and parrallel them for double the voltage rating. But at around $80 US
per cap it is probibly wiser to just buy a commercial cap. Has anybody
had any problems with the Condencer Products caps at 15KV?
 Learning the hard way,

 David Trimmell <dwt-at-efn-dot-org>