capacitor question

From:  baumann-at-proton.llumc.edu [SMTP:baumann-at-proton.llumc.edu]
Sent:  Wednesday, January 28, 1998 1:41 AM
To:  tesla-at-pupman-dot-com
Subject:  Re: capacitor question

On 28 Jan, Jim Heagy wrote:

> instead of building a bunch of caps and stringing them in series to get a hv
> rating, why can't you just stack alternate aluminum and plastic sheets, making
> connections to the outer two Al sheets only. it seems like this should give
> the same effect with a lot less construction involved.
> jim heagy

Jim: this is exactly what anyone building a plate cap does. 
There are 2 things involved that cause the decision (at least in my
case) to 'string together' multiple caps.

First (and foremost!) since muliple caps in series distribute the
voltage potential (and dielectric stress) equally along the series,
lower voltage capacitors may be used. Reducing the voltage across the
plates and the stress greatly enhances the potential life of the cap.
Remember that the high potentials across the caps will promote corona -
a Bad Thing That Shall Be Avoided.

Second: Just how big would you want that cap to be? My 0.007 cap,
which I figure is good to about 20KV (5x6mil sheets) is made of
3 internal 0.021 units, each consisting of 44 leaves of aluminum, 
with 220 sheets of plastic needed.. granted I was going for a cube
shape, not a tall-thin, but you get the idea. Had I chosen to 
make it a single cap, I would have been trying to keep 15 sheets
of plastic in place.. and had a 6" thick stack to try and control
I don't even want to think about it.

[ and of course, I just re-read your post.. and wonder if you meant
to have a number of 'lay' sheets in there.. this does not
increase capacitance enough. ]
Michael Baumann  Optivus Technology Inc.|Loma Linda University Medical Center
San Bernardino, California. (909)799-8308 |Internet: baumann-at-llumc.edu