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Skin effect (was:Primary and copper)
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From: Jim Lux [SMTP:jimlux-at-earthlink-dot-net]
Sent: Wednesday, April 01, 1998 9:59 AM
To: Tesla List
Subject: Re: Skin effect (was:Primary and copper)
> The problem is that this alone doesn't give correct results for long
coils. I have
> a secondary coil, made with rather thin wire, where I get Rdc~=Rac=142
Ohms
> (Rdc measured, Rac calculated) at the resonance frequency. Measurements
of
> the coil characteristics by several methods give a consistent result of
> Rac~=1000 Ohms at the resonance.
> I know that the formula is imprecise at this condition, and that the
proximity
> of other wires in a closewound coil increases Rac by a good factor, that
> dielectric losses in the PVC form add some resistance too, and that there
is some
> radiation resistance. But I don't know yet how to take these effect in
account.
For a close wound coil, I suspect that you could, at some level, treat it
as a long cylinder of copper with the current flowing around the cylinder.
In this case, the adjacent turns "shields" the conductor of interest,
reducing the effective cross sectional area.
For radiation resistance and the effect of dielectric losses in the coil
form, perhaps some of the Corum's work, or reference to a text on antennas
(Kraus?) might be helpful.
FWIW, has any one tried modelling a tesla coil using something like NEC to
do a complete EM simulation?