McMaster Carr Mica Sheets

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
   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
   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