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Re: Primary and Secondary winding direction



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

warpath-at-wtp-dot-net wrote:

> I, too, have heard of the "1/4 wavelength secoundary winding".
> Could someone explain what this is and where it came from?

This particular myth apparently goes back all the way to Tesla, and
unfortunately, like the smallpox virus, is not quite extinct yet.
At present there is no known useful relationship between the wire
length of the secondary and its resonant frequency. 

Sadly, this notion, regularly peddled on tesla related web sites, can
still be found incorporated into tesla design software even today,
despite the fact that a quick check demonstrates that the resonant
frequency of the coil is typically between 20% to 100% higher than the
'wire quarter-wave' would suggest - the discrepancy being greater for
the larger h/d coils. This occurs because the mutual coupling between
the turns of the winding raises the effective velocity within the
solenoid well above that which the straight wire would possess - more
than offsetting the reduction of velocity caused by the increased
effective capacitance created by coiling the wire.

Pete Lawrence wrote:

> I myself fell for the "1/4 wave length secondary wire" myth, and ever
> since have been doubting as much as possible everything I read, and
> try to verify things with my own experiments as much as possible).

Well said! Sadly, Tesla coiling is a minefield of mysticism and pseudo-
science, in which all sorts of daft and faulty notions continue to be
pervaded, often by those who really ought to know better. The beginner
is well advised to follow Pete's example and cultivate a skeptical
attitude.

For more about the wire length myth, see

 http://www.abelian.demon.co.uk/tssp/misc.html

Concerning winding direction, it must be borne in mind that there is
both capacitive and inductive coupling between the primary and
secondary windings. In one winding sense these will cooperate, and in
the opposing sense they will oppose one another. Therefore we might 
expect to see a small difference in coupling factor when the relative
winding sense is reversed. Whether this effect is large enough to be
measureable I don't know. It would be fairly easy to test for.

Regards,
--
Paul Nicholson,
Manchester, UK.
--