PC board Capacitors
Subject: PC board Capacitors
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Mon, 5 Feb 1996 01:42:00 GMT
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Quoting rickh-at-ghgcorp-dot-com (Rick Holland):
> ... I wanted to share my discovery that double sided PC board
> blanks seem to make decent capacitors. I etch a 3/4 inch border
> on them and solder the leads on. I've used these on a 7.5kv
> neon with no breakdown. Of course, I have no idea what their
> efficiency is, but I imagine Mr. Quick has stumbled across this
> before and may have some data for us (I hope I'm not presuming
> upon Mr. Quick).
Ah well, since you stuck my name in there I feel I should
comment. This capacitor design is a simple extension of the foil
and glass caps of yesteryear. Reprints of these are constantly
turning up, one recent one was the 1994 booklet _HIGH VOLTAGE
CAPACITOR DESIGN HANDBOOK_ by K.R. Scott and printed by Lambda
Publishing. Circuit board capacitors are outlined.
While these work fine on smaller coils running lower tank circuit
voltages, they simply don't scale up very well. Problems include
the high RF dissipation factor of the dielectric (glass or
printed circuit board), and a large exposed surface area that
promotes corona losses. As I mentioned, for a smaller coil these
will work OK, but scaling up to get something like a .01 -at- 15kvac
is not really practical. You can't really stack them unless you
have circuit board blanks (no copper) that can be placed between
plates in the stack: even with blanks and oil submersion, you
can't escape the high RF dissipation factor of the dielectric.
The last word in homemade capacitors are plastic film dielectrics
submerged in mineral oil. They rate right up next to commercial
plastic film pulse discharge caps.
... If all else fails... Throw another megavolt across it!
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