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Re: Pri to Sec capacitive coupling
Tesla List wrote:
>
> Original Poster: Terry Fritz <twf-at-verinet-dot-com>
>
> Hi All,
>
> I measure the capacitance from my primary coil to my secondary
coil at
> 55pF. That seems high to me but I don't think I am doing anything wrong.
> Of course, all external connections are removed for the measurement.
>
> This brings up the effects that mutual CAPACITIVE coupling may
have in
> Tesla coil operation. We all always talk of inductive coupling but never
> of capacitive coupling.
>
> In my system (center grounded tap neon), the primary coil is
floating in
> such a way that as the starting turns on the primary are going negative,
> the outer turns or going positive. Perhaps this cancels the effects that
> such capacitive coupling would have. However, if one were to ground one
> end of the primary I would thing this would start to significantly affect
> coupling?
>
> Just a thought...
>
> Terry
The effect of mutual capacitance (in addition to inductive) coupling is
discussed in many texts on Radio Receiver design. Depending on the
magnitude and polarity, it can cause dips outside the normal pass band.
The value you measure may not be the effective capacitance, if you just
connected a bridge between primary and secondary. I suspect that most
of the capacitance is between the primary and the "low" end of the coil,
and hence won't have much of an effect. One easy way to tell would be
to put a Faraday shield (bunch of vertical wires, grounded at the bottom
end, between your primary and secondary. If this makes a significant
difference (other than perhaps a path for strikes from the upper
terminal). then mutual capacitance is having an effect. I doubt that it
does, but have never made measurements such as you have.
Ed