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Re: Something For Nothing
From: Mark S. Rzeszotarski, Ph.D.[SMTP:msr7-at-po.cwru.edu]
Sent: Wednesday, October 29, 1997 7:24 AM
To: Tesla List
Subject: Re: Something For Nothing
Hello Malcolm and all,
Malcolm stated in part:
>I have finally done a definitive test of
>a stacked spiral primary and it works extremely well. The something
>for nothing bit is that if you built the bundle of copper tube I
>bought into a single flat spiral you might scratch 50uH from it.
>Arranging it in two layers with a sheet of acrylic in between brought
>it close to 80uH simply by making use of mutual inductance. The
>tubing is 3/8". It came as a 2- layer coil that spiralled in on one
>layer then back out again on the next. If you lifted the outer turn on
>one side it would form what looked like an hour-glass.
I have built a few flat spiral coils and they have some interesting
properties. I have never stacked them before, however. Sounds like a good
idea.
Pancake coils tend to have rather high distributed capacitance (okay
for the primary, not great for the secondary). In addition, most of the
inductance is in the outer few turns while most of the A.C. resistance is in
the central few turns. For maximum inductance for a given wire length, the
coil winding thickness should be about 1/4 of the outer diameter.
I used one as a driver coil for a magnifier a while back: solenoidal
primary surrounding a flat pancake driver with the center lead of the
pancake leading to the extra coil. I got pretty good results but the driver
coil had a tendancy to arc rather easily due to lack of consideration on my
part of the high voltages encountered in a magnifier driver circuit.
Regards,
Mark S. Rzeszotarski, Ph.D.