Measurements of a cap's ESL, ESR (fwd)

---------- Forwarded message ----------
Date: Fri, 22 May 98 08:44:23 EDT
From: Gary Lau  22-May-1998 0834 <lau-at-hdecad.ENET.dec-dot-com>
To: tesla-at-pupman-dot-com
Subject: Measurements of a cap's ESL, ESR


I have done an experiment to determine the ESR and ESL parameters of my
tank capacitor.  This is a surplus unit, .01 uF, 100KVDC, 2.5"x5"x10",
marked F-C-I, KM14-1000-10, .01 MFD-100KVDC, DEC 1983.

To measure this, I hooked my cap to a 50 Ohm sine wave generator, in
series with a 54 Ohm resistor.  I monitored the voltage across the cap
with a scope and tuned for minimum voltage.  The applied voltage was 14V

I saw two minimums.  The sharpest minimum was at 1.9 MHz, with Vc = 0.3V.
This corresponds to an ESL value of 0.702 uH.

There was also a lesser minumum at 15.4 MHz, Vc = 5.4V, with a slight
maximum at 14.4 MHz, 15.0V.  Not sure what caused this.

For calculating ESR, the voltage across the 54 Ohm R at 1.9 MHz was 13.6V
while Vc was 0.3V.  Assuming the Vc at resonance is due entirely to
I*ESR, ESR comes out to 1.19 Ohms.  However, I think this measurement is
flawed (way too high) as the 0.3V waveform was distorted and likely due
to harmonics from the signal generator.

I'm thinking that ESL is the more significant parameter in terms of being
a predictor of a cap's usefulness in Tesla coil service.  I was wondering
if anyone else had made similar measurements of home-made or commercial
caps that I could compare my figures to?

Gary Lau
Waltham, MA USA