Re: Unusual capacitor dielectrics

To: tesla-at-pupman-dot-com
Subject: Re: Unusual capacitor dielectrics
From: Bert Hickman <bert.hickman-at-aquila-dot-com> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Sun, 01 Nov 1998 20:47:06 -0700
Approved: terryf-at-verinet-dot-com
Tesla List wrote:
> 
> Original Poster: Steven Ivy <adder_black_the-at-yahoo-dot-com>
> 
> Thanks for the info Bert.
> I guess that must be part of the story I heard about, not megajoules,
> but big never the less. Shame their cap didn't work out. I have
> sources that indicate that work in that area is still on going and
> funny thing about reports like the one you sited it seems like the
> negative results reports always seem to somehow get released to the
> public but good results just get a new classification as secret and we
> never get to hear anything about them : (
> 
<SNIP>

This could be - the latest references on this topic in my personal
library only go to about 1995. It could be that later work WAS
successful, or that successful results weren't published.

> 
> Since you seem to have access to some fairly obscure data I was
> wondering if there are any other liquids, preferably non-polar
> liquids, that have dielectric constants better than or equal to good
> plastics? It seems like immersing a bunch of parallel plates into a
> decent liquid dielectric would be a pretty easy way to make a
> capacitor. 

There are many kinds of liquid dielectrics, both polar and nonpolar,
that could be used. In order of increasing cost, these include petroleum
oils, synthetic hydrocarbons, halogenated hydrocarbons (non-PCB's),
silicones, organic esters, and phosphate esters. Most commercial higher
k capacitor dielectric fluids tend to be polar. Unfortunately, only a
few of these dielectric fluids are commonly available to the casual
experimenter, and fewer still are available and specifically refined,
dried, and filtered for dielectric applications. Examples of relatively
commonly available dielectric fluids include mineral oils, and silicone
oils (such as refrigeration oils). 

> I have heard of people placing a common aircore variable RF
> capacitor in oil to make high voltage variable capacitor but they
> failed to mention what effect the oil had on the value of the
> capacitance I would think that the value would most likely go up quite
> a bit. 

Typically, the capacitance of a high voltage variable cap increases by a
factor of 2.2-2.3 versus what it was in air when immersed in mineral
oil, and the breakdown voltage is significantly increased (easily 5-10X
or more depending upon oil purity). A number of coilers have made HV
tuning caps using this technique.

> How about wax potting not just as the final step but as a way
> to introduce a dielectric?

> 
> Later: Steve Ivy
> adder_black_the-at-yahoo-dot-com
> Dallas Texas
<SNIP>

Paraffin is an excellent, low loss dielectric. Unfortunately, it tends
to shrink as it hardens, often tends to entrap air, and becomes very
brittle at lower temperatures. As long as the impregnating technique can
overcome these problems, and the use is at room temperature or above, it
can work quite well. A solution of melted LDPE in paraffin has also been
mentioned as an excellent castable dielectric.

Hope this helps!

-- Bert --