Re: Conical and Pancake Coil Arguments... (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 18 Jun 2007 21:55:24 +0000
From: Jeff Behary <jeff_behary@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: Conical and Pancake Coil Arguments... (fwd)

Hey Peter,

Well done with the coil, the photos look good from the link.
Actually the cotton coverings worked perfectly for this.  The cotton acts 
like a "wick", and the oil can actually permeate it and flow throughout.  
(The same is true for hot wax)

The trick is to heat the oil first.  Around 100 degrees Centigrade works 
well.  No need to deep fry the coil(!), the heat just helps the oil to flow 
and permeate things.  Also, it helps to operate the coil on very low power, 
even a small 30 watt tank circuit will do.  (I have a modified Violet Ray 
circuit for this).  You'll find that the oil is agitated rapidly by the 
electrostatic action of the coil, and air bubbles tend to float to the 
surface from within should there be any voids.

Waxes are easier to work with than oil.  I highly recommend a portable 
induction stove for melting wax or heating oils or any resins.  They are 
lousy to cook with, but are very sensitive with their controls in that you 
can maintain a temperature safe to melt wax and not have it spontaneuosly 
combust - again 100 degrees C is more than enough for this.  The traditional 
method is a double boiler, but this gets a bit tedious.

Also, if you can maintain the heat of the insulation for some time air 
bubbles tend to get driven off too.  For example, place it in a warming oven 
and simply leave it there a few hours at a very low temperature.  This gives 
the insulating medium time to permeate everything properly.

[This is why polyester resins and epoxies are hard to work with at home - 
they often cure before they reach all of the internal spots of the coil, 
leaving massive voids]

When cooling wax or oil, it is best to do it slowly. With wax esp., cracks 
can form if it is cooled too quickly.  If using Paraffin wax, adding about 
40% stearic acid to the wax makes a very hard composition that resists 
cracking.  Also, if you have a nice container for the coil a mixture of 
paraffin oil (kerosene here in the US) and wax makes for a softer and 
cheaper alternative to pure wax alone.  Wax toilet seals work great for 
container coils too, they are more or less wax and oil mixtures.

Beeswax and rosin in equal parts is very expensive but makes the perfect 
insulation.  As we've mentioned, we have coils 100 years old that still work 
fine with this mixture - and they were stored in conditions that by all 
rights should have completely ruined them electrically and it thankfully 
wasn't the case.

Jeff Behary, c/o
The Turn Of The Century Electrotherapy Museum
http://www.electrotherapymuseum.com

>Your comments on pancake coils are of interest to me. I still have (in the
>loungeroom for the last 2 years or so) the materials for a 20 layer pancake
>coil to be immersed in oil.  What has been stopping me going further is the
>concern about air voids as you say.  I can see the rationale for cotton
>covered wire here but oil soaked cotton is not going to let air out easily
>either so it may not be the complete answer.
>Peter
>http://tesladownunder.com/Tesla_coils_intro.htm#Multilayer%20Tesla%20coil

_________________________________________________________________
Don’t miss your chance to WIN $10,000 and other great prizes from Microsoft 
Office Live http://clk.atdmt.com/MRT/go/aub0540003042mrt/direct/01/