Re: Oil Paper Caps.

From: 	Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: 	Friday, December 12, 1997 9:33 AM
To: 	Tesla List
Cc: 	RE.Davis-at-btinternet-dot-com
Subject: 	Re: Oil Paper Caps.

> From: 	Robert Davis[SMTP:RE.Davis-at-btinternet-dot-com]
> Sent: 	Wednesday, December 10, 1997 3:08 PM
> To: 	'tesla-at-pupman-dot-com'
> Subject: 	Oil Paper Caps.
> Dear All,
> I am half way through building a small coil (<100W) and want to build the 
> tank capacitor.  I want to build an oil/paper cap, I will be using Kraft 
> paper and Medical Grade Mineral Oil.  The capacitor will be enclosed in PVC 
> tube and sealed at each end.
> I intend to seal the unit with Outdoor Silicon Sealant, the label says the 
> product emits acetic acid on curing, do you think this will contaminate the 
> oil unacceptably?  If so, would two part epoxy resin be better?

I have used the stuff rather extensively, and it has never given me a 
problem. I use only the clear silicone sealant, and I buy it in the big
tubular dispensers meant to be used with a caulking gun. I have never
had contamination problems. The vapors dissipate without too much 

The surfaces must be dry and clean. If the surface is oily then you may
experience difficulty. I use the stuff for sealing in electrodes to
my flat plate caps. I do the sealing BEFORE any oil is added.

Epoxy works great too. The silicone sealant is quite flexible, and there
are places where it is superior to epoxy. And vice versa! Use the sealant
whenever you desire a degree of flexibility.

> I think electrically the silicon sealant should be OK, I think also it will 
> be resistant to oil leakage, is this correct?

Electrically it is excellent. For years I have used it in HV DC projects
to prevent corona. Again, I use only the clear stuff. Once it is set,
it is very oil resistant. I have samples inside oil filled containers
that have been hanging around for years. I have not noticed any degradation
other than a slight darkening over the years.

> Does any one know the dielectric constant of oil/paper?
> Does anyone know the break down voltage of oil/paper?
> If not, I will assume break down voltage half that of oil, for safety, and 
> dielectric constant to be the mean of the two.

Under separate cover I am sending you dielectric constant data in the
form of a table. I don't want to clog the Tesla list.

> Thank you in advance for your help, all comments appreciated.
> Best wishes, Rob Davis (UK)

I hope the above interspersed comments are useful to you (and others).
The key is to NOT introduce any oil until you have fully sealed
your container. 

By the way, a useful construction technique is to build a plexiglass
container and then surround it with a plywood box that is snug. That
way the stresses are on the plywood box, and you can get by with a 
thinner grade of plexiglass (and save money!). I recommend that
the HV terminals only go through plexiglass, however, as plywood
can absorb water from the air and become slightly conductive. I use
an outer plywood box that is sort of a "sleeve".

Hope this helps.
Fr. Tom McGahee