Dimensions of my flat spiral coil

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

Original poster: "David Thomson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-volantis-dot-org>

Hi Malcolm,

I have wound a total of four flat spiral coils so far (I'm winding two more
tomorrow.)  The experiments that I have described on this list were
performed on two particular coils.

Before I go on, I want to share that large is not necessarily better for
transformers of 15KV 60mA or less.  The inductance of my 29" coil was so
strong, or there is a strange effect on the voltage, that my LCR meter could
not take a reading.  Also, no matter what capacitance I used in the primary,
8 turns on the primary with a 15KV 60mA transformer could not start
oscillating.

My 13" coils have provided ample flat spiral action and can be put into
action with 3.5 turns on the primary and .026uF of capacitance in the
primary circuit.  I could not get a 15KV 60mA NST to start oscillations in a
flat spiral coil at the measured resonant frequency.  I've had to operate my
coils at about 3 times the resonant frequency to get any action.

The first 13" diameter coil is made from 21 gage magnet wire and wound from
the center out.  There is no inner radius other than the width of the 1/4"
brass machine screw.  The coil is single layer and there are no cross over
wires.  The finished coil has a slight oblong shape due to the difficulties
of winding.  It has a measured inductance of about 35mH.  The calculated
inductance was 5.7mH!

The second coil was 13.75" diameter and also made from 21 gage magnet wire.
The coil started with three independent strands connected to the 1/4" center
post.  All three were wound parallel in a single flat layer.  There were no
crossed over wires in this coil either.  It was actually easier to wind this
"wye" coil as I call it as three wires required 1/3 the number of turns to
complete the winding.  On this coil I ended the three wires at 120 degrees
(more or less) from each other.  This resulted in three different
inductances in each of the three wires.  The inductances were 6.20mH,
6.23mH, and 6.25mH.  Oddly enough, each of the three wires had pretty close
to the calculated inductance!

The purpose I originally intended for the wye coil was to feed it with three
phase alternator current.  Had I realized the inductance difference between
the three wires I would have had all three wires end at the same degree.

Even without running the above coils, just the fact of the inductance
measurements is odd in itself.  A single wound coil yielded, in this case, a
7 to 1 gain over the calculated inductance.  In the wye coil, each wire
measured close to the calculated inductance, but there were three of them.

I am very interested to hear the explanations for the discrepancies between
actual design and calculations from the skeptics.  If everything we need to
know about coils is already known, what is the simple answer to these
measurements?

When I characterized the frequency of the single wound coil, the resonant
frequency band was from 50KHz to 100KHz.  But I can't make the coil operate
at that frequency.

I look forward to your report as to the characteristics of your coil.

Dave

>That strikes me as being a very fair comment. So fair in fact that
I'm considering winding such a coil. First question: is it single
layer? Please post the physical winding details so it can be
duplicated. I will figure out the mechanics of winding it and when
time permits, do so and do some measuring. I've already decided to
wind a single wire job and run it as an extra coil as I described
earlier - just to make an interesting magnifier if nothing else.

Regards,
Malcolm