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Re: Coupling seems a bit high

Hi Bart,

Your numbers are not "too" surprising.  You are on the edge with 0.23 but
with 2 inch spacing, the fields are spread out a bit more than most so you
can get away with it.  This is interesting.  We usually try to keep
secondary to primary spacing fairly close but perhaps this limits our
coupling and promotes racing arcs more than is needed!!  Perhaps more
secondary to primary spacing is a good thing.  Hmmmmm...

Cheers,

	Terry

At 10:19 AM 03/12/2000 -0600, you wrote: 
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