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TC Negative Charge


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From:  John H. Couture [SMTP:couturejh-at-worldnet.att-dot-net]
Sent:  Friday, March 20, 1998 12:26 AM
To:  tesla-at-pupman-dot-com
Subject:  TC Negative Charge


  To All -

  There appears to be some interest in the details of the two types of tests
I used to find the negative charge on an operating Tesla coil. It is obvious
that it is not possible to test the terminal directly so indirect tests must
be used.

  In both tests a small Tesla coil was used. The TC secondary terminal was a
2 inch doorknob and the test terminal a 7 inch oblate on a plexiglas stand.
The two terminals were about 2 feet apart. The test oblate was connected to
an electrostatic voltmeter with the ground side connected to the bottom of
the secondary coil which was not grounded.

  The TC was operated for a short time to charge the test oblate. The
voltmeter indicated about 2000 volts. The E meter indicates voltage but not
polarity so an electroscope was used. The electroscope was charged with a
negative charge leaving the leaves fully open. When the electroscope was
brought near the charged oblate the leaves collapsed indicating a positive
charge on the test oblate.

  The test oblate and the secondary terminal are the two metal sides of a
capacitor with the air between acting as the dielectric. Because the test
obblate was positive the TC terminal would have to be negative. The
electroscope was also charged with a positive charge leaving the leaves
partially open. When brough near the charged oblate the leaves opened
further apart again indicating a positive charge on the oblate and a
negative charge on the TC sec term.

  To confirm the above results a different type of test was setup using a
25-0-25 microamp null meter. In order to have the meter indicate correctly a
simple ungrounded loop circuit was used. The loop consisted of the TC sec
term - TC sec coil - null meter- electrostatic voltmeter - test oblate - and
air dielectric back to the TC sec term. The positive terminal of the null
meter was connected to the bottom term of the sec coil which was not grounded. 

  With this setup if the null meter needle moved to the right the current
was coming from the TC sec coil and term and moving to the voltmeter and
test oblate and back to the TC term thru the air dielectric. This would
indicate the sec coil bottom connection was positive and the top of the coil
negative. As the sec term was connected directly to the top of the sec coil
the sec term would also be negative. If the needle moved to the left the
opposite was happening and the sec term would be positive. The loop circuit
was not grounded because this would complicate the circuit and give
incorrect indication at the null meter.

  Several tests were made and it was found that the null meter always went
to the right indicating there was a negative charge on the sec term during
TC operation. It should be noted that Tesla had the instruments at his
disposal to make the same tests with small coils.    

  John Couture