Re: Equivalent lumped inductance and toroidal coils (fwd)

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Original poster: Tesla List Moderator <mod1-at-poodle.pupman-dot-com>



---------- Forwarded message ----------
Date: Sat, 17 Jul 2004 20:01:41 +0100
From: Paul Nicholson <paul-at-abelian.demon.co.uk>
To: tesla-at-pupman-dot-com
Subject: Re: Equivalent lumped inductance and toroidal coils

Bart wrote:

> I think the approximation should read:
> Ldc~= mu * N^2 * rt^2/(2*r1)

Yes, that works better, I think that must have been
a typo.  But still the error against the more complete
formula is quite high.  Not that it matters because there's
no incentive to use it in preference to the other.

> time for measurement and verification.

Yes, I was hoping Jared might chip in some inductance measurements
of his coils.

> Also, is aircore preferred over say a foam core?

Doubt there's any difference as far as modelling is concerned.
I can't see us being able to compute the capacitance distribution
for this case very soon...

I don't seem to be having much luck with that expression for mutual
coupling between filaments, either.  

You know, one of these days we'll have to figure out how to use
the method of partial inductances, so that we can get away from
circular filaments and symmetry restrictions. Then we can calculate
the inductance of funny shaped things. Like for example OLTC primaries?

As for toroidal coils, I don't quite see where to go with those. They
don't seem to have much inductance for the amount of wire that goes into
them.

> If I get the itch to wind a toroidal coil, is there an approximate
> dimension desired (24 awg).

Have you got some particular experiments in mind?  We could of course
check out that inductance formula, and measure the velocity factors
for each mode.  Wonder what the Q factors are like - poor wouldn't
you guess?  But there's little hope of giving that class of coil our
customary detailed quantitative comparison with a model. 
--
Paul Nicholson
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