RE: Mutual inductance and K factor

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <couturejh-at-telocity-dot-com>


Weazle -

Thank you for sending me the test data from your coil. I am aware of Terry's
method for finding the mutual inductance but I am not very familiar with the
typical calculations. My notes on his method are buried somewhere in moving
boxes and I do not have his address for the test.

Your caculations appear to be incorrect in that the mutual inductance should
reduce instead of increase when the secondary is raised. Also, are your
coils pri to sec distance (1.0) and the pri inside radius (3.05) and outside
radius (7.55) of the used turns agreeing with the program outputs? I hope
that you can soon test your coil with my method which requires no
calculations by the user. With the proper amps (2.65 or 3.18) in the ammeter
you only have to read the mutual inductance uh from the DVM meter.

The program shows a mutual inductance of 83.57 uh (you show 32.36) for zero
inches distance of the sec above the pri and 66.15 uh (you show 42.97) for
1.0 " distance. The 32.36 to 42.97 should be a decrease not an increase in
mutual inductance. The K Factor of .075 to .100 should also be a decrease.

If Terry would give me the address for his method I can determine what the
calcs should be. Thanks Terry.

John Couture

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


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, October 24, 2001 10:36 AM
To: tesla-at-pupman-dot-com
Subject: Mutual inductance and K factor


Original poster: "J. B. Weazle McCreath by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>


At 01:05 PM 23/10/01 -0600, you wrote:
>
>Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<couturejh-at-telocity-dot-com>
>
>
>Weazle -
>
>Click on the following for tests of the mutual inductance and the K
>factor.  Your computer will need the Acrobat program.
>
>     http://www.mgte-dot-com/kfactor1.pdf
>or   http://www.mgte-dot-com/kfactor1.gif
>
>This test should give you the mutual inductance that agrees with the
>JHCTES Ver 3.3 TC program.  Two other tests that should be made are
>for finding the actual operating frequency and the K Factor.
>

Hello John, coilers,

The methods and formula that you refer to above are very similar to those
used by Terry in his method of determining mutual inductance and from it,
the K factor of the coil.  I wasn't able to measure the primary current
to the degree of accuracy shown in your setup, which allows for a direct
readout of the secondary volts as being the mutual inductance.

I chose to use a value of ten amps in the primary winding, as this made
the calculations as shown below easier to do.  Listed below this are the
actual measurements that I made at four different relative positions of
the primary and secondary windings.  In my coil's construction, coupling
is varied by moving the primary up and down.

The mutual inductance is found by:  M = V / (w * I)

Where:  M = Mutual inductance in Henries.
        w = Line freq. in radians per second (377 for 60 Hz.)
        I = The measured current in the primary in amps A.C.
        V = The measured secondary voltage in volts AC.

K can then be found by using the formula:  K = M / sqrt(L1 * L2)

Actual measurements taken from my coil are listed below.  All where
taken with 10 amps of primary current.

  No spacers under Pri. supports: Sec. V. = .122  Mut. I. = 32.36 uH.
  0.50 " spacers                : Sec. V. = .146  Mut. I. = 38.76 uH.
  0.75 " spacers                : Sec. V. = .154  Mut. I. = 40.84 uH.
  1.00 " spacers                : Sec. V. = .162  Mut. I. = 42.97 uH.

L pri. = 0.0165 mH. (16.5 uH.), L sec. = 11.27 mH. (11,270 uH.)

  No spacers under Pri. supports: K = .075
  0.50 " spacers                : K = .089
  0.75 " spacers                : K = .095
  1.00 " spacers                : K = .100

I believe my math is correct, but as I said before, it's not one of my
strongest attributes!  I'm wondering why the my figures differ so much
from the ones generated by your program?  You already have the other
parameters of my coil, so perhaps with these additional figures I've
provided, you can retry it and see what the outcome is this time.




73, Weazle, VE3EAR/VE3WZL

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  http://www.hurontel.on.ca/~weazle