Re: measuring secondary parasitic capacitance?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Black Moon by way of Terry Fritz <twftesla-at-qwest-dot-net>" <black_moons-at-hotmail-dot-com>


lol, thats the simplest thing to figure out.
Take ground wire, stick into one side of cap meter
attach secondary to other side :) now walk away as far as you can, and 
place it in whatever envorment your going to run it in as capasatance will 
change with envorment





>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: Re: measuring secondary parasitic capacitance?
>Date: Mon, 04 Nov 2002 08:16:45 -0700
>
>Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" 
><jwagner-at-cc.hut.fi>
>
>Hi!
>
>On Sun, 3 Nov 2002, Tesla list wrote:
> > Original poster: "Laurence Davis by way of Terry Fritz 
> <twftesla-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>
> > just out of curiosity i tried to measure the capacitance of a secondary.
> > my meter kept giving the out of range error, then at one point started
> > to give a reading.
>
>Probably a DMM? This means low frequency measurement, and the inductance
>of the coil dominating the capacitance => high current from DMM => it
>thinks there's a very high capacitance there.
>
>Maybe adding a resistor in series with the coil (say at least 500kOhm)
>will give you a better reading. But check first with a know capacitor that
>the reading is still correct. :)
>
>Real LC meters _might_ work better. Altough, the one I tested didn't, so
>I'm not sure about this...
>
> > it wasnt stable.  the lowest I read was .150 nf.
> > I didn't do the tesla calc thing on the secondary, but I would expect
> > two things.
> >
> > should be .015nf (or 15pf) or rounds 'bout there.
>
>As such, a good idea, but... Much depends on how you made the measurement,
>and what exactly you want to measure.
>
>The self capacitance consists of a lot of factors, see
>  http://www.abelian.demon.co.uk/tssp/pn2511.html
>
>Hooking up an LC meter right accross the ends of a TC secondary will give
>you _some_ reading allright.
>But, at 400Hz or so, the voltage distribution accross the coil is quite
>linear, so you get a different reading for capacitance than you would get
>at around f_res measuring frequency.
>
>OTOH, all depends on what you take "true self capacitance" is assumed to
>mean... ;o) Medhurst capacitance, free space self capacitance, etc.
>
> > I didn't do the tesla calc thing on the secondary, but I would expect
> > two things.
> >
> > should be .015nf (or 15pf) or rounds 'bout there.
> >
> > parasitic capacitance has to be measured with higher
> > voltage.
>
>Concur there. It doesn't depend on the applied voltage, but on geometry
>and surroundings and voltage (vs charge) distribution.
>
> > perhaps the lower voltage requires more sensitivity
> > to measure the capacitance than that of higher voltage.
> > or design a piece of test equipment to measure it.
>
>Hmm, well, you're right there. If your LC meter doesn't extend into the
>pF range then it's really hard to measure any pF's reliably. ;)
>
>But if you'r LC meter or DMM measures small 22pF capacitors correctly, but
>not the TC secondary, then there's something wrong in the measurement
>setup.
>
>Maybe the series resistor trick helps?
>
>cheers,
>
>  - Jan
>
>--
>*************************************************
>  high voltage at http://www.hut.fi/~jwagner/tesla
>  Jan OH2GHR


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