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

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Steve Greenfield wrote:
> This will measure capacitance to ground, but what
> about turn-to-turn capacitance?

The capacitance between neighborouring turns contributes very
little, 1% or so, to the total effective capacitance, at least in
solenoids.  We don't expect flat coils to be very much different,
because the voltage distributions are broadly the same.  The
turn-turn capacitance would start to become significant only
if most of the voltage was developed across just a few turns.

Usually, in solenoid coils the effective cap is around half
that of the DC, for example (data from tssp model):

System   H/D     Cdc     Ces at Fres    Ces/Cdc

pn1      1.4    69.2pF    30.1pF         0.43
pn2      2.8    94.6pF    41.5pF         0.44
tfltr    2.9    50.6pF    20.1pF         0.40
sk20b49  3.3    25.5pF    16.9pF         0.66
mm3      4.7    36.7pF    20.1pF         0.57 
tfsm1    6.1    29.3pF    12.1pF         0.41
mm1      8.9    20.4pF    11.6pF         0.57

For flat coil models, I have only two, tentatively, because the
software is still under test,

System   H/D     Cdc     Ces at Fres    Ces/Cdc
dt1      0.0    12.7pF    8.5pF          0.67
mm5      0.0    20.6pF   13.9pF          0.67 

--
Paul Nicholson
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