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Re: Safety Gap
From: Edward V. Phillips[SMTP:ed-at-alumni.caltech.edu]
Sent: Monday, November 17, 1997 1:27 PM
To: tesla-at-pupman-dot-com
Subject: Re: Safety Gap
"Yes I have matched the capacitor to the neon for Max power transfer.
I was also wondering that if I only run the coil for a minute or so
at time if I could use a larger capacitor. The neon is a 10,000Kv 50ma.
This give a source impedance of 200000 Ohms and at 50Hz a
capacitor of 15nF. But the transformers DC resistance if only 5.6K.
The inductance is greater than 20H (off the scale on meter)"
1. With the "matched" capacitance you have a series resonant circuit
composed of the reactance of the transformer - 200000 ohms, the capacitive
reactance - (-) 2000000 ohms, and the transformer resistance of 54600
make that 5600 ohms. It the transformer did not saturate with the
higher voltage you should be able to get a maximum voltage of
10000 x 200000 / 5600 with the spark gap opened so it won't fire.
Of course, the transformer (core) will saturate or the transformer
insulation will fail long before the maximum voltage is reached. Point
is, a "matched" condition such as you have set up is an ideal way to
blow up the transformer and/or capacitor if you aren't careful and
if you don't use a safety gap which "almost fires" at the normal
transformer output voltage. [I see an error above. The capacitive
reactance should have read 200000 ohms!] Of course, the transformer
reactance isn't exactly 200000 and varies with output voltage, but
still a dangerous condition for the unwary.
2. The transformer inductance is equal, in principal, to its
leakage reactance (200000 ohms) divided by the frequency in
radians/second, or 2*pi*f. In your case the value comes out
to be:
L = 200000/(2*pi*50) = 636.6 henries.
Ed