Re: for Inductance Calculation

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Mddeming-at-aol-dot-com>

In a message dated 4/13/01 9:00:05 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes: 



>
> Hi Matt and everyone, 
>
>    The formula L=Nr*2/9r+10h........for a single layer air coil. 
>
> Matt, the 9 and 10 in the denominator equation, are those a constant of 
> some sort??? and of what sort??? 
>
> This is the formula I have;  L=N(squared) x permeability x A / l 
>
> L is inductance in henries 
>
> N is # of turns 
>
> Permeability is a constant of 1  (for air cores) 
>
> A = area of core 
>
> l = length of coil 
>
> Anyway, 
>
> Wade



Hi Wade! 
        As I said, this is a quick and dirty, convenient numerical 
approximation, accurate for single layer, air core coils. It is from the time 
before PCs when practical calculations were done with a pencil and gray 
matter. There are more complex formulas that are 1-2% more accurate. It's 
just like using 22/7 ~Pi instead of 3.1415926535.... 

The formula I gave can be found in: 

1.     Tab Handbook of Radio Communications.  by J.J.Carr (K4IPV) 1987 
2.     Modern Tesla Coil Theory by Duane A. Bylund 1990 
3.     Old ARRL Handbooks 
4.     Most older texts on radio communication written for technicians. 

If you use the formula, don't forget the proper parentheses. (Nr)^2/(9r+20h) 

Matt D.