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Re: Capacitance of Tesla secondary coi
Original poster: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>
Partha Sarkar wrote:
> I want to calculate the inter-turn capacitance of the
> secondary windings, or the capacitance between any two
> turn on the secondary.
For the capacitance between neighbouring turns, the Palermo
formula is an approximation,
C = 2 * pi^2 * epsilon * coil_radius / (ln(a) + sqrt(a^2 - 1))
where a = 1/spacing_factor = winding_pitch/wire_diameter
and ln() is natural log. See A.J. Palermo, 'Distributed
Capacity of Single-Layer Coils', Proc IRE 1934, Vol 22,
p897; I can probably email you a scan of this article if
you need it.
Palermo's experimental measurements are dubious, but the
above formula has a straightforward derivation.
However, this direct turn-to-turn capacitance only becomes
a significant determining factor of the propagation
characteristics at high frequencies - well above the quarter
wave fundamental axial mode resonance used by Tesla coils.
For the resonant modes involved in coiling, the longer range
internal capacitance is much more significant - this is the
combined effect of the large number of small capacitances
between the pairs of well-separated turns.
Bart Anderson's JavaTC program will calculate the
quarter wave resonance of conical coils,
To see the secondary C calculations that go into this,
Also, Antonio Carlos M. de Queiroz has some excellent
physical L and C calculators at
None of the above formulas/programs take account of E-flux
passing through the coil former dielectric. They assume
'air cored' coils, ie thin walled tubes.
Hope that helps,