Re: Flat spiral vs Solenoid Wire Length/Inductance Observations

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

To a first order, yes, you could look at a flat spiral as a solenoidal
coil....  But, the significant thing that you're not handling is the
different configuration of  mutual inductance between turns, which does have
an effect on the overall inductance.  In both cases, turns that are farther
apart don't have as much flux linking them.

The standard Wheeler approximation equations are also quite similar...

Both have inductance that is roughly proportional to N^2, which is the
dominant thing.. In fact, if the turns were all collocated(infinitely thin,
and in the same place), the inductance of a N turn inductor would be N^2
that of a 1 turn inductor of the same dimensions.  All physical realizations
have to spread the turns out somewhat, reducing the coupling of the turns,
so the inductance will be less...

That said, I'll bet, without looking in detail at the problem, that there
are fairly significant ranges of dimensional parameters (no doubt those that
crop up in tesla coiling) where the approximation you propose would be
within 10%..


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, October 20, 2002 6:48 AM
Subject: Flat spiral vs Solenoid Wire Length/Inductance Observations


> Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
>
>
> Is it not true that the inductance and length of wire in a flat spiral can
be
> deduced by considering it a solenoid with same average diameter/number of
turns
> as the flat spiral?
>
> In the course of winding my spiderweb TC primary I used formula wl
=2*pi*r*n to
> calculate the total wire needed to complete the winding where wl is the
average
> radius of the spiral, r the average radius and n the number of turns;
>
> And if the wire needed for flat spiral with maximum Q ie. with width to
radius
> ratio of 8:11 were calculated with the method above would this be the same
as a
> solenoid with maximum Q i.e. height to radius ratio of 9:10?
>
> The wire on my spiderweb primary is wound spirally on a flat board of
minimal
> thickness -is there any reason why the inductance should not be equal to
L=
> r^2*n^2/[8*r+11*w] -the same as for a flat spiral?
>
>
>