Re: Inductance of a capacitor? (fwd)

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Original poster: Gerry Reynolds <greynolds@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Sun, 17 Dec 2006 16:17:41 +0900
From: Peter Terren <pterren@xxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Inductance of a capacitor? (fwd)

Some big caps like my pulse caps come with the inductance stamped on the 
side.
http://tesladownunder.com/PulseCapsAerovoxlabel.jpg
The individual caps are 80 + 40 + 40 nH in parallel. To calculate the 
inductance of the whole bank and associated wiring I measure the resonant 
frequency.  This was 25 khz (period 45 us) for the 215 uF. it is measured by 
looking at the ring frequency on the CRO with a small energy discharge into 
the wire short circuit. This gives 200nH wheras the sum of inductances was 
160nH.
For a smaller cap like a TC tank cap just scan with a frequency generator 
and a resistor in series and watch for the voltage peak across the cap at 
resonance should give the resonant frequency and the inductance can be 
calculated back from that by
F (freq in Hertz) = 1 / {2 * pi * sqrt [ L (Henries) * C (capacitance in 
Farads)]}

Peter

> ---------- Forwarded message ----------
> Date: Thu, 14 Dec 2006 19:23:50 -0700
> From: Terrell Fritz <terrellfone@xxxxxxxxxxxxxxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Inductance of a capacitor? (fwd)
> Hi,
> You just "resonate" it...  "Typically" it is done with high dollar network
> analyzers for fancy caps with "Q"s that really cannot be measured...  But
> say 100nF at 10nH resonates at 5MHz...  Pretty easy to do with simple
> equipment with caps like we use.  The signal generator's internal
> resistance (50 ohms) might be a problem in some cases for the
> measurement.  But in general, for the caps we like, pretty simple test
> equipment can resolve the resonate frequency of the cap and thus the
> internal "L"...  But really, it is always too small to "care" for us...
>
> Cheers,
>         Terry
>
> ...........
>
>>It is my understanding that capacitors have some - even small - amount of
>>inductance.
>>
>>Anybody know how to calculate such inductance amount?
>>
>>Tnx,
>>Steve