Re: More Coupling...

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

> Ed Phillips <evp-at-pacbell-dot-net> wrote:
> 
> > I suppose one could do it by computing M for each of the turns and
> > then summing it,
> 
> Indeed. That's how my little acmi [3] program works. It's quite
> accurate for a closewound coil of many turns, ie a secondary.
> Primaries built from thick wire or pipe are likely to be less well
> modeled by the current filament approximation used in the program.
> 
> > but that sounds like a lot of work and have never tried it.
> 
> Not really all that much effort for me, largely due to the efforts
> of a chap called Grover who went to the trouble of making up a set
> of tables [1] for inductance between concentric current filaments.
> acmi is just table lookup and summing.

	Grover (and BS C74) have occupied honored places on my book shelf for
many years!  I'll look up Grover's tables at work tomorrow.  I never
really studied that part; just copied his formulae and tables for
solenoids.

> 
> > I see a lot of fellows using flat primaries, and wonder how much
> > coupling they actually get.
> 
> Me too. I welcome info on measurements of M (made at low frequency)
> to help get a feel for the accuracy of acmi. At tesla operating
> frequencies, inter-winding capacitance rears its head to complicate
> matters. I don't have a good handle on that one yet [2], so getting
> the right overall coupling is still a matter of trial and error as
> far as I'm concerned.
> 
> Just for fun, I used the (recently fixed) acmi to produce a graph of
> k factor against separation for a pair of flat coils [4]. The coupling
> at close range seems asymptotic to about 0.68 for this choice of turns
> and radii. A larger outer radius gives a higher maximum coupling. If
> this trend is real and not an artifact of the program, then some quite
> small separations are needed to achieve the k factors required for a
> magnifier secondary. Some real measurements to confirm this picture
> would be very nice.
> 
> Please note that k calculations of the type done by acmi, which assume
> a uniform current in each winding, are only approximately valid for
> tesla secondaries due to the non-uniform current prevailing at high
> frequencies [2]. Hence the need to measure M at frequencies well below
> the self-resonances of the windings involved.
> 
> [1] F.W. Grover, 'Inductance Calculations', 1946;
>     Reprinted by Dover, 1962.
> 
> [2] tssp will be addressing these issues in the near future.
>     http://www.abelian.demon.co.uk/tssp/
> 
> [3] http://www.abelian.demon.co.uk/acmi/
> 
> [4] http://www.abelian.demon.co.uk/tmp/n10x40x100.gif
> 
> Regards,
> --
> Paul Nicholson,
> Manchester, UK.
> --

Thanks for the dope.

Ed