Re: Small TC experiments

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

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

Ed Phillips <evp-at-pacbell-dot-net> wrote:

>>> ...If you keep the winding dimensions the same the inductance goes
>>> up as the square of the number of turns, while the resistance only
>>> goes up as the wire diameter.  Net result is that the Q stays the
>>> same.

> This applies exactly to the ratio of the inductances of two coils
> of the same dimensions, ...

Of course. Apologies - I should have read your post more carefully.

> ... and also assumes that there is no insulation on the wires to
> reduce the winding factors as the wire diameter goes down.  See
> Grover [71], p 117 and others on following pages.  Of course, the
> inductance of a long coil of variable length doesn't go up as N^2.
> There's the little factor of Nagaoka's constant, etc.

> By the way, have you seen the expression for a very accurate
> closed-form calculation of Nagaoka which was in IEEE Proceedins a
> few years ago?

I have 

 'Inductance Formula for Single Layer Circular Coil'
 HC Miller,
 Proc IEEE, 1987, Vol 75 pt 2, pp256-7.

which uses a straightforward iteration of the elliptic integrals to
obtain both the bulk inductance and the mutual between filaments.

I haven't actually tried the method outlined so I don't know how it
compares with Grover - something else on my things-to-do list!

When it comes to calculating the Nagaoka inductance, I'm fond of
Lundin's formula, given in 

 'A Handbook Formula for the Inductance of a Single Layer Circular
  Coil',
 R. Lundin,
 Proc IEEE, 1985, Volt 73, pp1428-9.

which presents a neat little formula for the inductance which is
claimed to be equivalent (to 6 figures) to interpolation over the 160
values of the original Nagaoka tables. I've found Lundin's formula to
be very reliable and easy to use.

Regards,
--
Paul Nicholson,
Manchester, UK.
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