RE: New Inductance Formula

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

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Malcolm,

>Sucker that I am, I tried your formula on two different coils and it
appeared not to work. Perhaps you would like to show us
all the fine details of the arithmetic as applied to the following helical
coils:

Thanks for helping out.  That's why we're supposed to bring our stuff to
peers, so our mistakes can be pointed out.  As seen in a previous post, the
formula wasn't correct.  This formula gives the same values as Wheeler's
formula except in the correct units:

                   (N*R)^2 * 2.46063
henry = --------------------------------------
        ((9*R)+(10*H)) * c * Cd * pi^2 * 10^-1

Coil 1: 4 turns, radius 13", height 5"

                   (4*13in)^2 * 2.46063
henry
= --------------------------------------------------------------------------
--
        ((9*13in)+(10*5in)) * 2.99x10^8 m/s * 2.112x10^-4 siemens* 3.14159^2
* 10^-1

                   2704 in^2 * 2.46063 / 39.370079
henry
= --------------------------------------------------------------------------
--------------
        (117 in + 50 in) * 2.99x10^8 m/s * 2.112x10^-4 siemens * 3.14159^2 *
10^-1

                 169 m^2
henry = -------------------------------
        167 m * 6.25 x 10^4 coul^2/kg*m

                1.012 m
henry = -----------------------
        6.25 x 10^4 coul^2/kg*m

        .000016192m
henry = -----------
        coul^2/kg*m

        .000016192 kg m^2
henry = -----------------
             coul^2

henry = .016mH

>and Coil 2: 980 turns, radius 4.9", height 45"

46.669mH

Dave