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

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

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