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: "Metlicka Marc by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <mystuffs-at-orwell-dot-net>

> I have found that i get the best readings with the coil placed directly
> on my ground grid placed on the floor, I connect one lead to one wire of
> the coil (base or top) and connect the other to the grid. The grid is
> not connected to external ground, just the meter. For the flat coil i
> placed it on a teflon ring that i have to allow some space and connected
> the same. I use twisted pair wire for the leads of my gen rad cap bridge
> and this gives the best results.
> I have also found that i can get fairly accurate toploadC readings
> reading without and then with the topload in place, I first tried this
> last year while getting tssp measurements, mostly because i didn't know
> it wouldn't work?

It seems that you are measuring the capacitance between the coil and
the ground plate, when the distance between them is small.
In a practical Tesla coil using a flat secondary, the distance between
the coil and the ground would be larger, and so the capacitances would
be smaller. You should make the measurement in a configuration similar
to the normal one for an operating coil. Anyway, this measurement puts 
all the coil at the same potential, while in a Tesla coil one of the
ends 
is at zero potential.
The measured capacitance in this way results to be about twice the 
"self-capacitance" of the coil.
Twisted wire adds significant capacitance, that must be discounted
from the readings.

Antonio Carlos M. de Queiroz