Re: Cap materials

Subject:  Re: Cap materials
   Date:  Wed, 16 Apr 1997 09:48:20 -0700
   From:  Bert Hickman <bert.hickman-at-aquila-dot-com>
Organization: Stoneridge Engineering
         To:  Tesla List <tesla-at-pupman-dot-com>
Gary Lau wrote:
> I'm about to start building some rolled poly caps, and have a question
> about sourcing materials.  .09" thick polyethelene is not commonly
> available, but .006" thick is.  Is it reasonable to use 16 layers of
> this thin stuff, or would this many layers be totally unwieldy?
> I don't have access to a vacuum pump to pump the cap down to remove >the bubbles.  Would the multi thin layers pose a greater problem in
> harboring air bubbles?
> Also, for the mineral oil, what kind of place does one go to for this?
> Auto supply store?
> Gary Lau
> Waltham, MA


A number of thin sheets of dielectric is better than 1 or two
thicknesses of thicker material. The flat plate caps I use each 4 mil
thick material, since this was very easy and economical to get. 8 layers
are used per plate cap, and 4 caps are tied in series to yield a total
thickness of 132 mils. 96 mils is probably more than adequate for even
15 KV Neon use as long as you make sure you've eliminated most of the
air between the layers. I originally was going to make rolled caps out
of this material, but trying to wind the multiple thicknesses proved to
be very frustrating, and totally unsuccessful. A couple of coilers have
reported success making rolled caps from stacked layers of this stuff,
but a high degree of skill and patience is warranted (and I lacked a
sufficient amount of either!  : ^) ). 

If you orient the materials so that the plates are vertical, air can
escape naturally over a period of time, especially during a lower
voltage break-in period in Tesla Coil use. This lets you get by without
needing a vacuum pump.

Mineral oil can be purchased at Veterinary supply places, drug stores,
and petroleum products dealers. Local utilities also use this oil for
transformers, and will often sell you some (or even give you some). 
Transformer oil brand names include Shell Diala-X or AX, Exxon Univolt
60, Esso Voltesso 35. For Tesla Coil caps, pure USP mineral oil, like
Tulco Lubsnap 100, Shell MVI-65, or USP Veterinary Grade will work just
fine. Even baby oil will work - and it smaells alot nicer that Diala-AX!
Some coilers have even used plain old SAE 10 or 20 weight engine oil,
this often contains additives that may degrade its perfomance in Tesla
Coil capacitors. Let your fingers do the walkin' in the Yellow Pages -
you should be able to find a number of sources - go with the cheapest

Safe cappin' to you!

-- Bert --