K Quiz

To: tesla-at-poodle.pupman-dot-com
Subject: K Quiz
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 20 May 1997 23:58:18 -0500
Approved: tesla-at-stic-dot-net
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:

Primary coil A:
     flat pancake coil, 10 turns, inside diameter = 12", outside
diameter=22"
     Lp=56.6 uH

Primary coil B:
     flat pancake coil,  5 turns, inside diameter = 12", outside
diameter=22"
     Lp=15.8 uH

Secondary coil #1:
     solenoidal coil, 24" tall, 8" diameter, 888 turns #22 wire, Ls=45.8
mH

Secondary coil #2:
     solenoidal coil, 24" tall, 8" diameter, 566 turns #18 wire, Ls=18.7
mH

Secondary coil #3:
     solenoidal coil, 24" tall, 8" diameter, 288 turns #12 wire, Ls= 4.8
mH

where: uH is microhenries, mH is millihenries and dimensional units are
in
inches.

     Assume the bottom turn of the secondary coil is aligned with the
plane
of the flat
pancake primary coil for all cases.  For primary coil A used with
secondary coil
#1, I experimentally measure K=0.23 with M=375.2 uH.
     My question is this, what happens to K as we try the different
combinations
of primaries and secondaries above?  Think about it.  (BTW, I know what
the
answer is!)

Primary   Secondary        K
   A              #1               0.23
   B              #1                  ?
   A              #2                  ?
   B              #2                  ?
   A              #3                  ?
   B              #3                  ?

Regards,
Mark S. Rzeszotarski, Ph.D.