Re: The manufacture of capacitors

To: tesla-at-pupman-dot-com
Subject: Re: The manufacture of capacitors
From: Richard Wayne Wall <rwall-at-ix-dot-netcom-dot-com>
Date: Tue, 10 Dec 1996 15:58:37 -0800

You wrote: 

>Re: Oil dielectric capacitors
>	Why not go the whole way and eliminate the solid dielectric
>material between the plates?  I have an article in an old (circa
>1921) QST describing an 0.01 mfd, 30 kV capacitor using only oil
>as the dielectric.  Quite a construction job  to get the plates
>flat enough to avoid excessive average spacing, but genuinelyh
>genuinely indestructable!!!!!!  By the way, this one worked at
>the "special" wavelength of 350 meters, or about 857 kHz, so the
>inductance must have been pretty small.
>	Why doesn't some get ambitious?  Or, more likely, will
>someone who HAS been ambitious describe his results.
>Ed Phillips
>

12/10/96

Ed,

I've put some big cheap hamfest air variables in plastic cases and have 
done just this by adding oil.  Voila!  An oil variable cap.  The 
capacitance increases at a ratio of about oil k over air k (1).  But 
not as much as you might think.  The larger air caps can often be 
disassembled and reassembled with smaller washer spacers so the oil gap 
can be made smaller.  But, a point of deminishing return appears as oil 
break down voltage is somewhere around 5 kV.  I thought of using SF6, 
but its not worth the time and expense.  

If you make a fixed oil cap you may consider several sections in 
series.  Also, the oil has to be boiled or otherwise desicated and the 
cap has to be sealed against moisture.  

Getting the right design and getting rid of all the poly, air bubbles, 
vacuum etc., would a boon to home cap builders.  We certainly know how 
to build salt water caps, so why not switch it around and use a liquid 
dielectric rather than solid and metal plates rather than salt water 
plates?

Let us know how it works out if you build one.

RWW