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QUESTION ABOUT POLYETHYLE

Quoting Ed Harris:

 EH> Hi all,
 EH> I was looking over the notes on building polyethylene
 EH> capacitors in Chip's FAQ and I was puzzled by something. 
 EH> I believe Richard comments that after the mineral oil is     
 EH> added and one pumps the cap with a vacuum pump, the cap will 
 EH> "outgas" for quite some time. In fact, it seems that         
 EH> Richard says they will contine to outgas to some
 EH> degree for as long as he has has patience to pump.

I don't think those are my words. The file you are looking at is
most probably from a Texas coiler by the name of Bert Pool. Bert 
and I have  some differences of opinion reagrding capacitors,
vocalized when we met a couple of years back at Richard Hulls'
lab in Virginia.

 EH> What is outgassing? The oil,or the poly? 

Neither. Even a very tightly rolled, or highly compressed stacked
plate capacitor ends up with trapped air between the plates and
the dielectric. This air may in fact be in the form of a thin
"film" of air molecules rather that trapped "bubbles". The
capacitor is not fully broken in until oil has been completely
soaked through the entire cap, and all trapped air has been
displaced. The oil must work it's way through so that all of the
surface area where the plates and dielectric are in contact are
"floating" on an oil layer perhaps only a few molecules thick.

I have tried constructing capacitors where oil was brushed over
all of the plates and dielectric prior to assembly. Caps built in
this manner do not require excessively long break-in periods, but
they are nearly impossible to work with: plates and dilectric
slip and slide out of position, and a nice tight, high value,
capacitor is virtually impossible to make. 

Richard Quick


... If all else fails... Throw another megavolt across it!
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