distributed capacitance... was Re: secondary question

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

This distributed turn to turn capacitance will cause some self resonance,
but I think the dominant capacitance effect on a tesla secondary (other than
the top load) is the capacitance of the secondary to ground (aka the
Medhurst capacitance).  For all intents and purposes, the secondary acts
like a big conducting cylinder sticking up at right angles to a ground plane
(i.e. the primary, or maybe a real ground plane).


> Since the TC secondary looks and behaves like a distributed
> capacitor, each pair of adjacent wires is a mini cap and the
> charging and storage of the charge of these mini caps depend
> on the dielectric constant (this would be the wire insulation
> and air gap between the wires and also dependent upon the
> resistivity of the coil form), you would have a gradient charge
> on the coil.  The higher the resistivity of the coil form the
> less drainage of the capacitance and thus the longer it will
> maintain a charge. This would explain why the higher up
> you go the more intense the shock and why some coil forms
> are less susceptible to the effect. Looks something like this:
>
> GND-----|-----|(------|-----|(-------|----|(------|--0
>                 |----res-----|----res------|----res----|
>
> where 'res' is the coil form resistance/interwinding leakage
> and --|(-- capacitance of each winding pair and '0' is the top
> load.  So, if you have a 1000 turn secondary you would
> have 500 mini capacitors in series.