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Measurements of a cap's ESL, ESR (fwd)
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From: Gary Lau 25-May-1998 1447 [SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Monday, May 25, 1998 2:25 PM
To: tesla-at-pupman-dot-com
Subject: Re: Measurements of a cap's ESL, ESR (fwd)
>> From: Gary Lau 22-May-1998 0834 <lau-at-hdecad.ENET.dec-dot-com>
><snip>
>> 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?
>
>From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
>I would say that ESR is by far the more important parameter of the
>two. It directly relates to internal dissipation in the cap. ESL is
>only a tiny fraction of total tank L. Any R = a power loss. I haven't
>measured any of my Tesla caps but will make a note to do so when time
>permits.
>
>Malcolm
Hi Malcolm:
I agree, ESR is certainly related to internal power dissipation, but I
thought the real culprit in cap self-heating was dielectric losses? I
didn't mention this previously because I had no idea of how this is
measured, given that it is frequency-dependant. My (flawed) technique
for measuring ESR could only work at the cap's self-resonant frequency.
Or is ESR and dielectric losses actually the same thing?
While a cap's ESL is certainly small as compared to the tank inductor, I'm
seeing in PSpice simulations that parasitic tank inductances outside of
the primary (like ESL) have a profound effect on things.
Terry Fritz's measurements using fiber optic probes have shown that a gap's
conduction ceases briefly at each zero current crossing at the tank Fres.
Each reignition of the gap excites high frequency oscillations due to
parasitic L's and C-self of the primary. I believe significant losses
occur due to this, and this is the reason it's so important to have very
short and beefy tank wiring, minimizing stray L's.
If ESR of a cap is high, then it may well be the more significant
parasitic and I was wrong to discount it, especially if it's another name
for dielectric losses.
Regards,
Gary Lau
Waltham, MA USA