Tank caps -- teflon and Kapton

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Mark Snoswell by way of Terry Fritz <teslalist-at-qwest-dot-net>" <mark-at-cgCharacter-dot-com>

Hi... OK I am about to go a bit over the top on the tank caps.

I have just received my first roll of Teflon -- wow!.. I have never seen
any film hold a static charge like the Teflon does. It's a roll of
0.001" film 6" x 425 foot... I got it directly from Dupont. For anyone
interested it cost me about A$180 -- on today's exchange rate that's
about US$106.

I also have a roll of Kapton -- 0.00065" film 9" x 1000M.

These films were actually intended for other projects -- but I might as
well use them for tesla tank caps.

Now to my question: ... Has anyone else had experience with creating and
running caps from Teflon and Kapton?

In particular I am looking for empirical data on lifetime vs. applied
potential... Dupont's data for Kapton shows that the CSV (Corona Start
Voltage) is about 5% of the dielectric strength (DS = breakdown
voltage). To achieve a long lifetime (1000's of hours) you must not
exceed the CSV... But at just 5% of the DS that's a pretty big reduction
in working voltage! -- OK, I know I can stress the film for short
lifetime TC caps -- but it's a logarithmic scale so you cant increase
the working voltage much without approaching 1 hour life time pretty
quickly!... So is there anyone out there with practical experience with
Kapton in TC caps?
As it is the Kapton film I have has a DS of 4.8 KV  but a lifetime
working potential of just 272 V

Try as I might I can't find the CSV for Teflon... Can anyone help here?
The film I have has a DS of about 6.8 KV but I have no idea what the
corona characteristics of Teflon is as you approach the DS -- can anyone
help?  (I got the film to make 600V caps originally). Even with a
de-rating to 600V working voltage I have enough film to make about 0.02
uf at 20 KV -- with a DS of 200 kv. I have some large bus bars and
copper shim so that this cap will be about the best possible for HF and
pulse applications.

cheers

Mark

PS. A little practical tip for making plate caps -- spray a small amount
of Teflon on the film and then roll out all the air -- this yields just
as good results as you can get -- compared to "dry" pressure
construction you can improve the capacitance of Kapton film plate caps
by almost 10x with this method. You do have to make sure that all the
solvent from the Teflon spray is removed -- it's heptane and very
flammable/explosive.

---------------------------------------------------------------
Dr Mark Snoswell.
Creator & Head Dude                        www.cgCharacter-dot-com