RE: Tesla Coil K Factor (was: I've lost my k. Can someone help me find it?)

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

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>


Paul -

You have apparently misunderstood my test data regarding the K factor. The
results of the  test I show below are for the "two resonant mode" (two
humps) test and not the open/short test. The calcs are comparing my calc
method with your calc method that you posted. The open/short test is a
different test and the calcs use different equations. These equations are
also shown below.

The two "Two mode" test equations
  JHC    K = (F2-F1)/Fr
  Paul   x = F2/F1    K = (x^2-1)/(x^2+1)
These JHC and Paul equations gave results with about 0.7 percent difference.

The open/short test equations
  K = sqrt(1-(Fo/Fs))   or  K = sqrt(1-Ls/Lo))
The Fo and Fs frequencies are different frequencies than the F1, F2, and Fr
frequencies.

Note that I am not advocating any of the methods to find the K factor. In my
post to Dan I showed four different methods to find the K factor without
recommending or advocating any of the methods.

John Couture

--------------------

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, September 25, 2002 4:15 PM
To: tesla-at-pupman-dot-com
Subject: Re: I've lost my k. Can someone help me find it?


Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<paul-at-abelian.demon.co.uk>

John Couture wrote:

> The results of K factor tests of one of my coils. I calc a
> K of .1720 compared to .1708 using your calcc method. About
> 0.7 percent difference.
>  F1 = 425
>  F2 = 505
>  Fr = 465

>  K = (F2-F1)/Fr = (505-425)/465 = .1720

The above is correct when F1 and F2 are the two secondary
resonant frequencies obtained with the secondary top is
open-circuit and short-circuit, in the way John describes
below:

> Look for a resonant frequency with the secondary coil ends
> open with no connection and also the resonant frequency with
> the secondary coil ends connected together.

Please don't confuse these with the two resonant mode frequencies
which comprise the beat envelope.  The mode frequencies are the
two resonances that you will detect if you sweep the coupled coils
with a signal generator (primary gap closed and the secondary with
its normal topload and grounding).  This latter method is much
better than the one you suggest, because it reports the actual mode
frequencies that appear during operation.  When F1 and F2
refer to the mode frequencies (as opposed to the short/open test
frequencies) then k is calculated with

   x = F2/F1;
   k = (x^2-1)/(x^2+1);

This represents the real k factor that is in effect during operation.

I hope everybody has got this clear now!  There are two different
methods here, one which the original question referred to, and the
other which John is advocating.  Two different formulas.
--
Paul Nicholson
--