Re: Transparency Caps

To: tesla-at-pupman-dot-com
Subject: Re: Transparency Caps
From: Jan Florian Wagner <jwagner-at-cc.hut.fi> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Sat, 12 Feb 2000 09:53:40 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Jason,

> After hearing about anothers (someone on the list but can't 
> place the name :-) recent succes w/ some plate caps using 
> overhead transparencies and either Al foil or flashing, I 
> was wanting to try it myself on my small coil. The only 
> problem is that I don't know what the transparencies are 
> made of and what the dielectric strength/constant would be 
> for them.

Well, not really sure about the _exact_ dielectric constant and strength
for different sheet types/materials, depends pretty much on the
manufacturer, but "generally" for an A4 sized sheet of which the inner
part 1" away from the corners is used, you should get 4-6nF per sheet -
and as C = e * (plate surface)/(sheet thickness) you could calculate the e
dielectric constant from this.

About RF losses, someone (can't remember the name, sorry) had the
idea of placing a sheet in the microwave oven and see if it warms
up. If it get's warm or hot, it's not the right material for TC RF
conditions.

Regarding the voltage: in my assembly I have 800VAC accross each sheet
and it works well - no corona, at 8kVAC input to the sheet stack. I did
also some tests with a car ignition coil, and a single sheets seem to
stand at least 15kV pulses, and also tiny tesla coil streamers. But
if it handles a constant 2kVAC or so is another thing - it pretty sure
won't.
A "rolled cap" maybe is a not so nice a thing to try with those sheets.
You probably have to either cut the transparency roll to sheets, or fold
it.

A stacked capacitor, remotely like those MMC style HV caps, would be the
way to go. 

See www.hut.fi/~jwagner/tesla and there Coil description, under tank
cap, for some (vague for now) details.

greetz,
Jan