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Re: Dialectrics in Plate Capacitors
Tesla List wrote:
>
> Original Poster: Apollo <ollopa-at-jps-dot-net>
>
> I have two sheets of 60mil 4'x8' HDPE. I need to make a capacitor for
> my 15kv 60ma NST. I'd like to make a .02uf capacitor, but I'm not sure
> if I can. Will I need to put two caps in series to handle my NST?
>
> Since I have 60mil HDPE, there's no way I can roll a cap and I've decided
> that I'd rather build a stacked plate capacitor anyway. My research
> suggests that I should let the poly hang over the foil by at least one
> inch on all sides, but I don't understand why this is necessary if I submerge
> the plates in an oil with a dialectric strength equal or greater than that of
> the poly. If it won't puncture .06in of poly, why will it arc from end
to end?
> What if there was only a quarter-inch of poly overhang that was sealed with
> silicone sealant?
>
> Thanks - Rick Richard
Hi Rick...
first off your 15KV NST can develope up to 30 KV + in the cap due to
resonate rise and those wonderful secondary to primary strikes... all
the oil does is reduce the formation of corona that WILL develope at the
corners of the metal plates in the cap. and Silicone sealant it
doesnt work that close to the metal plates in the cap for some reason
HV loves to eat it ( besides you need the oil to saturate the spaces
between the plates and plastic sealing would only trap in air )
I did some calcs for flat plate cap at 60 mils
K=2.2 Dth =.060 Area = 81sqr " X 32
you need approximately 32 aluminun plates -at- 9"X 9"
34 plastics -at- 11.5"x11.5" considering you can get 32 12X12's out of a
4X8 sheet of plastic you are looking good
the uF would be approximately .0201 +- 5% depending on how clean
construction is
Scot D