Re: measuring secondary parasitic capacitance?

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

Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi Larry,

88pF is high. If your secondary is say inside a room or garage with a 
topload mounted and with a primary, I would expect about 27pF or so. As a 
bare secondary (alone in the universe), then something like 8pF is real and 
the dc meter should measure about 15pF. But the reality is, it's not alone 
in the universe. There's a groundplane, probably walls, a ceiling, objects 
here and there, etc... It all adds up. IF you had the coil surrounded in an 
enclosure about 40" all around the coil, then you might hit about 35pF with 
all the components on the system.

I found this note at RadioShack regarding your model: (see operation).

        The lowest capacitance ranges have an internal capacitance that is
        the actual input capacitance of the instrument.  If you want to
        make measurements at very low ranges, subtract the internal
        capacitance from the measurements.

So, if you can find out what the internal capacitance is.....

Just go to www.radioshack-dot-com and search on   22-174. Your meter should 
come right up (search the on-line catalog). There's a lot of info on your 
particular model.

Take care,
Bart


Tesla list wrote:

>Original poster: "Laurence Davis by way of Terry Fritz 
><twftesla-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>
>
>tried with a series connected 10m carbon film resistor.
>meter consistently read 88pf +- 1.
>sec spec: 4.5" coil form, 20" winding length, 30awg heavy build.
>IIRC 1200 or so turns, around 1350ft.
>meter is a radio shack dmm, model 22.174 rev b.
>
>higher than i expected. perhaps a more accurate meter would help.
>larry.
>
>>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.
>>
>>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. :)
>>
>>Maybe the series resistor trick helps?
>>
>>cheers,
>>
>>  - Jan
>>
>>--
>>*************************************************
>>  high voltage at http://www.hut.fi/~jwagner/tesla
>>  Jan OH2GHR
>
>
>
>