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



---------- Forwarded message ----------
Date: Sun, 24 May 1998 17:31:04 -0600
From: terryf-at-verinet-dot-com
To: tesla-at-pupman-dot-com
Subject: Re: Measurements of a cap's ESL, ESR (fwd)

Gary and Bill,

        According to my muRata data book, the ESR for NPO and other typical
ceramic leaded caps (low voltage) ranges from 0.05 to 0.2 ohms.  Jennings,
ATC and the High power RF types run at 0.005 to 0.02 ohm.  ESR can be almost
impossible to measure when the Qs get above 1000.  They usually run high RF
currents through them and guess at the Q judging by how hot the caps get.
Skin effects and all the parasitics mess up measurements with plain test
equipment. Usually when we press the high power cap guys for Q numbers the
say greater than 2000.  They really don't know the Qs accurately at all.
Best just to run it and see if it heats up too much.  If you need the
numbers for modeling, look in data books for similar caps.  They all run at
about the same range.  For most uses the ESR can be ignored or a rough guess
will do.  I would guess about 0.1 ohm for the one mentioned.  The other
circuit resitances are probably more significant.

        Terry




At 09:31 PM 5/22/98 -0600, you wrote:
>
>
>---------- 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
>
>All:
>
>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
>P-P.
>
>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?
>
>Regards,
>Gary Lau
>Waltham, MA USA
>
>