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Re: Coupling seems a bit high
Bart:
This sounds accurate. Similar to some 12 and 14 inch dia coils we have used
in the past.
As an example, on a 24 inch dia coil we found we need to be approx 8 to 8
1/2 inches above the horizontal plane to set the coeff. of coupling for best
performance.
Most coils I have seen above 10 inch dia are definitely overcoupled. Most
tuners never check this very important factor.
Dr. Resonance
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Sunday, March 12, 2000 5:22 PM
Subject: Coupling seems a bit high
>Original Poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net>
>
>Hi all,
>
>Yesterday, I decided to measure the mutual inductance on my coil and was
>surprised at how high the coupling value ended up. I used the method of
>120VAC, 60Hz into the primary with R and meter in series. Measured the
>current at 10.95A. Then with 1uF, 10k ohm resistor across secondary, I
>measured the voltage. Here's what I got:
>
>Bottom of secondary 1 inch below primary = 2.59V
>Bottom of secondary even with primary = 2.24V
>Bottom of secondary 1 inch above primary = 1.99V (Typical running setup)
>
>Using M = V / (w * I) for mutual inductance
>(w = 377 radians per second at 60 Hz), V = Sec. V, I = Pri. current,
>and using
>K = M / sqrt(Lp * Ls) for coupling coefficient, the following was found:
>
>At 2.59V, M = 627.4uH, K = 0.302
>At 2.24V, M = 542.6uH, K = 0.261
>At 1.99V, M = 482.1uH, K = 0.232
>
>Coil size is 12.5" x 43.5" using a flat spiral primary with 2" spacing. I
>use a pole pig and typically run with bottom of the secondary about 1"
>above the primary. This is the point where racing sparks don't occur.
>
>The K of 0.232 seems a bit high to me. Has anyone else found they can run
>at this high of K? It may have something to do with the coil size and power
>levels used. Just curious if this seems high to others in your typical run
>modes.
>
>Thanks,
>Bart
>
>