Re: Increasing Capacitance...
From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Friday, September 19, 1997 2:43 PM
To: Tesla List
Subject: Increasing Capacitance...
> From: bmack[SMTP:bmack-at-frontiernet-dot-net]
> Sent: Sunday, September 14, 1997 10:42 PM
> To: Tesla List
> Subject: Re: Glass/poly and more...
> To All
> A while back , perhaps 5 moths ago, I made a saline cap from
> a very tall cylindrical wine bottle (Rene' Junot). The outside was
> wrapped in aluminum foil, water softener salt was poured in to the
> shoulder level, then water added to cover, motor oil filled
> the remaining space as a sealant.
> A small hole was drilled in the cork, and a #12 bare copper wire
> was forced through it . The wire was then worked down the length
> of the bottle as the electrode.
> I then let it "settle" and it seemed that the air bubbled up into
> and out by itself! (cork was not fully installed).
> Next step was AC seasoning with about 5KV for a few hours at a
> Shortly after it's construction and preping, it measured 680 pf.
> I must mention that was never used in TC service, but sat on the
> floor for those 5 months. Now it reads 1200 pf.
> Guess using a wine bottle makes it get better with age. (I'm
> Maybe the copper reacting with the salt is making copper cloride
> lowers the internal resistance and thus the impedance seen by the
> I know you were looking for oil cap experiences, but I thought I'd
> little experience in the ring anyway.
> Jim M
The above post has resulted in a number of subsequent posts in which
various reasons have been put forth for the Growing Capacitance of
Jim's salt water capacitor. While I have found the posts on the
possible influence of WATER interesting in their own right, I have
found it somewhat amazing that all the replies so far have focused on
what might possibly be going on INSIDE the bottle.
May I turn everyone's attention to the OUTSIDE of the bottle for a
second? You will note that Jim's bottle capacitor is covered on the
outside with aluminum foil. This method of constructing saltwater
caps is notoriously BAD because it is very difficult to get the
aluminum foil to come into good contact with the surface of the
glass. As many readers of this list know, you can increase the value
of your saltwater caps by NOT using aluminum foil, and instead
immersing the base of the bottle in its own saltwater solution.
When you use aluminum foil, a considerable portion of the interface
is Foil/Air/Glass/Salt Water. The real culprit here is the AIR
between the Foil and the Glass. My guess is that as Jim's saltwater
cap has Aged, it has probably picked up some moisture that has worked
its way between the Foil and the Glass. Anything that displaces the
Air is probably going to increase the capacitance of the saltwater
cap. Heck, I bet if you built two saltwater caps and just dipped the
foil for the second one into saltwater or water or even oil before
applying it to the second cap that you would find the capacitance of
the second cap was much greater than the first. The maximum of course
would be to do away with the foil completely and just immerse the
bottle in saltwater up to the level of the saltwater INSIDE the
If you find the saltwater immersion method too messy for your tastes,
then liberally coat the outside of the bottle and the inside of the
aluminum foil with something like Spar Varnish (or your favorite HV
insulator). The HIGHER the dielectric constant, the better. Measure
the capacitance of this type saltwater cap, and note the improvement
in capacitance value.
Does anyone out there notice the similarities here between THIS post
and my posts concerning Richard Smit's idea for a poly/glass
capacitor? Richard Hull, I believe in one of your tapes you
disassembled an OLD HV cap that had an extremely high capacitance
value for its size. It was a rolled affair, and I believe your
conclusion was that the darn thing was using an oil with a very high
dielectric constant. I think we coilers would do well to identify
which oils out there are readily available that have the higher
dielectric constants. Sunison appears to be one that has a constant
of about 4. Castor Oil is even higher. Alfred Skrocki mentioned that
he also used Sunison oil successfully. But he didn't mention whether
he noted the increase in capacity over using regular mineral oil or
With the cost of Tesla capacitors being fairly high, even when they
are homemade, it just seems to me that we coilers should be
aggressively investigating what oils we can use that will give us an
appreciable increase in capacitance. Would anyone who has First Hand
knowledge of an oil with a dielectric constant greater than say 2.2
that has successfuly been used in Tesla coil capacitors please post
to the List, or e-mail me at tom_mcgahee-at-sigmais-dot-com with as many of
the details as you can recall. Thank you.
Hope this helps.
Fr. Tom McGahee