Re: Equivalent lumped inductance and toroidal coils

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

Original poster: Bart Anderson <tesla111-at-sbcglobal-dot-net> 

Hi Paul,

Yes, the approximation for inductance need not be used. You hypothesized a 
typo, so I just figured if true, it would be easy enough to find (it was).

As for measurements, I agree that it would be great if Jarad could perform 
some of these since his coils are already wound. If he decides to do so, I 
hope he would seek measurement advice prior to taking measurements. That's 
something I always like to do to ensure everyone is on the same page.

My hat is off to Jarad for building outside the norm with his toroidal 
shaped coil. It captured our attention as any new shape might. It came with 
his best reasoning, which is great he's thinking about the physics of the 
coil. Others might wind a coil of this nature to simply see how it would 
perform and not care to even think about the physics. I hope he researches 
more about what was mentioned in various posts.

I agree the inductance is an obvious measurement and easy enough to 
perform. I also agree the Q will most likely be low. The capacitive 
distribution will be interesting considering the turn to turn arrangement 
as well as the even distribution around the coil. Should be rather high.

I'll begin looking around for a suitable form. If following measurements, 
the coil ends up impractical, it should still make a decent topload.

Take care,
Bart

Tesla list wrote:

>Original poster: Paul Nicholson <paul-at-abelian.demon.co.uk>
>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
>--
>
>