# Re: K Quiz

```Subject:  Re: K Quiz
Date:   Thu, 22 May 1997 18:42:32 +0000
From:   "John H. Couture" <couturejh-at-worldnet.att-dot-net>
To:   Tesla List <tesla-at-pupman-dot-com>

At 04:58 AM 5/21/97 +0000, you wrote:
>Subject:  K Quiz
>  Date:   Tue, 20 May 1997 14:14:03 -0400 (EDT)
>  From:   msr7-at-po.cwru.edu (Mark S. Rzeszotarski, Ph.D.)
>    To:   tesla-at-pupman-dot-com
>
>
>Hello coilers,
>        Here is a little food for thought.
>     "K" is the term applied to the degree of magnetic coupling between
>the
>primary and secondary coils of a conventional tesla coil (or the primary
>and
>driver
>coil in the magnifier configuration).  Typically, we aim for values
>between
>0.1 and
>0.25 or so for a conventional tesla coil, and 0.4 or higher for
>magnifier
>primary/driver coil systems.  "M" is the amount of mutual inductance
>between the
>primary and secondary coil.  We define:
>K = M / SQUARE_ROOT [ Lp x Ls ]
>where Lp is the primary inductance, Ls is the secondary inductance,  M
>is the
>mutual inductance, and K is the coefficient of coupling between the two
>coils.
>
>Consider the following scenarios:
>
------------------------------------  Big snip
>
Regards,
>Mark S. Rzeszotarski, Ph.D.
>
----------------------------------------------------------------

Mark -

Your "K Quiz" would have delighted Tesla because the quiz includes one
of
the many TC parameter combinations that point out the character of Tesla
coils. Your Quiz was apparently inspired by my "K Factors" post about a
week
ago.

In my post I stated that the K factor could be changed by only
changing
the number of secondary turns instead of the relative positions of the
pri/sec coils. This is based on the conditions that the wire size remain
the
same and only the number of turns and length of winding change.

So when I saw the length of secondary winding did not change in your
quiz,
I figured you had found an interesting combination of parameters where
the K
factor did not change. I immediately went to the JHCTES program and
discovered this was true. You had reversed engineered the problem to
find
these special TC parameter combinations, no easy task. I was pleased to
find
that there are coilers on the Tesla List that have the ability to do
this.

I do not want to minimize the importance of the coilers that build and
test Tesla coils. The data obtained from this work is invaluable in
developing  a coherent picture of how the TC works. The pursuit of both
theory and practice of coiling is necessary if Tesla coils are to be
used
for anything except for spectacular electrical devices.

The equation you used   K = Lm/sqrt(LpLs)  has two unknowns K and Lm
that
are difficult to find. You said that you actually tested for the K
factor.
There are several ways to test for the K factor. I would be interested
in
which method you used.

It might interest you to know that the JHCTES program also gives you the
necessary pri capacitor, operating frequency, Q factor, log dec, and
several
other interesting TC parameters for your pri/sec coil combos. Many other
interesting TC characteristics can be explored with the program. The
program
coordinates 46 TC parameters and keeps them all in tune at the flick of
a
mouse. However, it takes some study of how the program works to get the
most
out of it.

John Couture

```