# Re: Primary calculations

• To: tesla-at-grendel.objinc-dot-com
• Subject: Re: Primary calculations
• From: mrbarton-at-ix-dot-netcom-dot-com (Mark Barton)
• Date: Fri, 19 Jan 1996 01:57:51 -0800
• >Received: from ix12.ix-dot-netcom-dot-com (ix12.ix-dot-netcom-dot-com [199.182.120.12]) by uucp-1.csn-dot-net (8.6.12/8.6.12) with ESMTP id CAA22664 for <tesla-at-grendel.objinc-dot-com>; Fri, 19 Jan 1996 02:58:23 -0700

```Ed,

I'm really surprised you find Wheeler's formula in error.  I have found it is
quite accurate even when pushed to weird dimensions and aspects which you are not
doing.  Are you sure you are using the radius of your coil and not the diameter
in the formula:

L(uH) = (r^2) * (N^2) / (9*r + 10*h)

where:
r = coil RADIUS in inches
N = number of turns
h = coil height in inches

If I'm being obvious and insulting, please ignore this message, but occasionally
even the best of us misses something.

Zap,
Mark

===================================================================

>
>Does anyone have a formula to calculate the inductance of a primary wound on
>a cylindrical form?  I am talking about 3/8" copper tubing wound on a 6.2"
>dia form with 3/8" spacing between turns.   Wheelers formula doesn't seem to
>work.
>
>Thanks,  Ed Sonderman
>

```