Re: poly cap
Professional cap builders use 1.0 mil dielectric and build up 2-3 layers to
make a single "cap element". This cap element normally has 20 times the
capacitance required. 20 such units are series connected to produce the
The 2-3 layers helps insure flashover protection in the event of an impurity
in the dielectric material. Each cap element generally has a voltage rating
of 1,200 volts RMS . With 20 units in series the overall DC rating would be
in excess of 50-60 kV. The ACrms operating potential for such a cap is
around 20 kV which makes them suitable for use with neons and pole xmfrs.
The oil used to fill these caps is constantly stored under vacuum to prevent
any moisture from entering. The caps are vacuum impregnated in cases and
sealed ---- under oil to prevent any air or moisture from entering. You
could probably skip this step for personal use, but the details in para 1 &
2 will give you a near bullet-proof cap construction.
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Saturday, June 12, 1999 3:04 AM
Subject: Re: poly cap
>Original Poster: Bert Hickman <bert.hickman-at-aquila-dot-com>
>Tesla List wrote:
>> Original Poster: "Kevin Wahila" <knw2-at-lehigh.edu>
>> What is the best poly thickness to be used in a rolled cap with a 9kV
>> kevin wahila
>It depends to some extent on the thickness of the poly that you're using
>and how "bulletproof" you want to make your cap. Thinner sheets of poly
>actually have a higher breakdown voltage (in volts/mil). Also, it's
>critical that you have at least 2 sheets of poly between plates to
>prevent a single dielectric defect from destroying your cap. I'd
>recommend using at least 50-60 mils of poly if you're using 25-30 mil
>material. If you're using 6 mil poly or thinner, you could reduce this
>to 35-50 mils. You can always go thicker... going thinner simply pushes
>you closer to the edge of breakdown but saves on the initial cost and
>size of the cap.
>In any case, it will be inmportant to remove as much entrapped air as
>possible by either drawing a partial vacuum or by running the cap
>vertically and using an extended break-in period at lower power levels.
>Safe cappin' to yoi!
>-- Bert --