Re: Measuring self-capacitance directly (Re: flat secondary)

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

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

Coil capacitance is a real problem to measure direct. The only way I know
how to do it is indirectly. I use copper tape and etched board  coils for
high frequency because the edge to edge capacitance of the turns is small
while the current carring cross section is high,providing high "Q". Round
wire should have common edge to edge and side to side capacitance so a
measuring plate on the side should be aproximitly the same measurement. If
measured on one side only away from the ground with a plate the same size as
the coil and no over-lap.
    Robert  H 

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Sun, 24 Feb 2002 22:34:19 -0700
> To: tesla-at-pupman-dot-com
> Subject: Re: Measuring self-capacitance directly (Re: flat secondary)
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Sun, 24 Feb 2002 22:46:09 -0700
> 
> Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
> 
> Tesla list wrote:
>> 
>> Original poster: "Steve Greenfield by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <alienrelics-at-yahoo-dot-com>
>> 
>> I must admit I'm confused.
>> 
>> This will measure capacitance to ground, but what
>> about turn-to-turn capacitance? Or is this just meant
>> as sort of a rule-of-thumb sort of measurement? Isn't
>> it likely that a flat coil will have a very different
>> self-capacitance than a solenoid coil?
> 
> The turn-to-turn capacitance has a small effect only
> in a coil with many turns and a single layer.
> An example: Assume a turn to turn capacitance of
> 100 pF (quite big), and a coil with 1000 turns. You have
> then 1000 100 pF capacitors in series. The total
> capacitance would be then 100/1000 = 0.1 pF. The body
> capacitance of a typical coil is much larger.
> 
>> I wouldn't expect connecting your cap meter across the
>> leads of a coil to work, regardless of AC or DC output
>> of the meter.
> 
> Ok, but a meter could be designed to make valid measurements
> in this way. An inductance meter can measure an inductance
> with a capacitance in parallel, by using only low-frequency
> signals in the tests. A meter using high-frequency signals
> could measure a capacitance, even with an inductance in
> parallel with it.
> 
> Antonio Carlos M. de Queiroz
> 
> 
> 
>