# Fw: New Inductance Formula

```Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>" <scepp-at-mts-dot-net>

Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jwagner-at-cc.hut.fi>

*This is a REPOST since the first one got messed up from word rap around.*

Hi Jan, Dave, and the list,

I've modified and tested this one for all metric units.

1.55*10^-3 * (N*R)^2 * kg * m
L = --------------------------------------
[(354.3*R)+(393.7*H)] * coul^2

(R and H in _metres_, N is unitless)

Obviously it's more complicated that the original, a person could round off
some of the multiplication factors, like Jan had done to make it look more
...nice, and easier to use. I've left then as they worked out to be, this
way to keep it accurate.

contra

> >>               (N*R)^2 * 10^-6 * kg * m
> >> henry = -------------------------------
> >>               [(9*R)+(10*H)] * coul^2

> >> The units N, R, and H are still in inches.

> >Because a Henry is defined as m^2 kg / Coul^2 and Coul=s*A

Also Henries are measured in Webers per Ampere which is Magnetic flux per
ampere, Which is also equal to Volt econds per ampere.  Also What Dave
derived and another version too.  See below.

Wb            V  *  Sec
L =    -------   =  --------------  =
Amp              Amp

Kg  *  m^2                   Kg * m^2
-------------------  = -------------------  =  Henries
Coul^2                Amp^2 * Sec^2

-- These units I obtained from a physics text and Circuit analysis book.

I have a question about Wheelers formula, In Modern Resonance Transformer
Design Theory, a 1985 version, it uses in the demoninator  [8*a + 11*b]
instead of 9 and 10, is this an older version of the equation or slightly
different application?

This discussion got to me so I had to look it up.

*This is a REPOST because the original message got messed up from word wrap
around.*

Shaun Epp

```