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McMaster Carr Mica Sheets
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From: Hollmike [SMTP:Hollmike-at-aol-dot-com]
Sent: Wednesday, April 01, 1998 12:32 PM
To: Tesla-2; tesla-at-pupman-dot-com
Subject: McMaster Carr Mica Sheets
Hi coilers,
I have recently discussed the use of mica sheets obtained from McMaster-
Carr as a dielectric in a plate cap. The catalog claims 20kV per mil
dielectric strength. I, however, just proved otherwise by accident. I set up
a full-wave bridge rectifier using 10kV diodes from my 12kV neon. As I raised
the voltage to the neon, everthing was fine until I reached full voltage.
The peak voltage was at 19.7kV(perhaps a wee bit more). I heard the fizz of
the dielectric puncturing and shorting two of the plates. No damage occurred
to anything(except of course the sheet of mica), but I thought those
interested should be aware that the 4 mil thick sheets of this mica should be
considered to have a maximum of 20kV per SHEET, not per mil thickness. I had
intended to use 3 layers between each of the plates, but must have suffered a
brain fart at one point while assembling my cap. It has been fixed now and
checked for the right number of layers. I will be testing it again later(
after allowing it to sit for awhile as the capacitance tends to rise with
time).
Incidentally, 5kV per mil dielectric strength is consistant with values I
have seen for mica, so it makes sense not to assume the value given by the
catalog.
I believe that three layers of this mica will prove to be adequate for 15kV
neons, but I will post results when I confirm this. I hope it works well as
this makes for a nice compact cap. It also is easier to put together than
rolled caps and can be assembled under mineral oil to eliminate air bubbles.
A 0.01uF cap can be made with 8 plates of 4 X 6 inches using three layers of
this mica. I cut 1 inch radius curves on the corners of the plates to reduce
stresses so the area is 23.1416 sq. inches per plate.
Party on!!!!
Mike Hollingsworth