Re: Hurray, I destroyed my homemade cap!

To: "'Tesla List'" <tesla-at-poodle.pupman-dot-com>
Subject: Re: Hurray, I destroyed my homemade cap!
From: Tesla List <tesla-at-stic-dot-net>
Date: Sun, 30 Nov 1997 16:16:34 -0600
Approved: tesla-at-stic-dot-net

From: 	Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: 	Sunday, November 30, 1997 10:22 AM
To: 	Tesla List
Subject: 	Re: Hurray, I destroyed my homemade cap!


> 
> From: 	Rick Holland[SMTP:rickh-at-ghg-dot-net]
> Reply To: 	rickh-at-ghg-dot-net
> Sent: 	Saturday, November 29, 1997 5:36 PM
> To: 	Tesla List
> Subject: 	Re: Hurray, I destroyed my homemade cap!
> 
> Tesla List wrote:
> > 
> > From:   Adam[SMTP:absmith-at-tiac-dot-net]
> > Sent:   Thursday, November 27, 1997 12:56 PM
> > To:     Tesla List
> > Subject:        Re: Hurray, I destroyed my homemade cap!
> <SNIP>
> > So then, how about solid corona protection, like paraffin wax?  I could
> > get this cheaply at the grocery store, melt it in a double boiler and pot
> > the cap.  This would make the cap a lot more difficult to repair, but if
> > I over engineered it in the first place it should survive a few years of
> > Tesla use, right?.  I am using 120mil of very high quality LDPE (4 x
> > 30mil) and operating at 9kV, so my cap is not likely to blow anytime
> > soon.  Mostly I just want to make something without that horrible oil!!!
> 
> Adam,
> 
> I don't know from personal experience, but all the old texts I've read
> recommend a 50/50 mixture of paraffin and bee's wax, applied just as you
> describe. They all warn against scorching, though. The nice part to this
> approach is that when melted and hot, the combination flows like water,
> and should be much easier to wick than oil. As a matter of fact, it just
> occurred to me that heating the capacitor oil might improve wicking.
> Hmmmm.
> 
> -- 
> 
> 	Rick Holland
> 
> 	The Answer is 42.
> 
> 

Rick & Adam,
The advantage of oil is that it is fluid. With any form of solid 
insulation you have to be aware that even a pinhole in it can lead
to catastrophic failure.

I have used beeswax to insulate things like Oudin coil resonators
and some HV DC capacitors that I built many years ago. I have not
tried using beeswax for Tesla coil capacitors, but I am sure that
such a cap would be better than a dry cap, but not as rugged as 
an oil filled cap.

Paraffin is much too brittle, I would think, and the beeswax is
fairly expensive. A 50/50 combo would be cheaper than beeswax alone,
and might be do-able. If *I* were trying to fabricate such a dry
cap, this is what I would do:

Build it as a flat plate cap. Use Kraft paper in the construction,
between all surfaces. Each sheet of Kraft paper should be soaked
in liquid wax and applied while still warm and liquid. Apply heat
and pressure, and build up the cap a layer at a time, always keeping
the level of liquid wax in the container high enough that it covers
the layer being added. Final assembly would ideally involve holding
the unit together under high compression while it was allowed to
SLOWLY cool.  If all air could be expelled and the unit sealed
tightly in say a plexiglass container, then you might have a decent
capacitor. Hopefully any heating would simply re-melt the wax and
thus actually help keep the cap free of bubbles. It would not
be as good as an oil filled cap, but for small portable applications
it might be reasonably useful.

Note: The container itself could be the source of compression.
Maybe 1/2" thick frame of plexiglass so you could really tighten
the screws, so to speak :)

I am not sure if plexiglass will distort under the kinds of
heat that would be used in the building of this type of cap,
but the only way to really find out is to build one and see what 
happens.

By the way, As the wax cools it will contract and tend to form
concave depressions at the surface. You might have to compensate
for that by adding more molten wax as the cooling progresses.

Hope this helps.
Fr. Tom McGahee