Re: My first TC

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

Original poster: "William Swanson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <swansontec-at-yahoo-dot-com>

Hi All,
Here are all the juicy details you wanted about my
Tesla coil with the flat secondary...

The secondary is 45 turns of 24 AWG magnet wire spaced
1/3" apart, for a total wire length of about 200 feet.
The coil is wound on a form consisting of sixteen 1/4"
dowels 24" long arranged like the spokes of a wheel.
The "hub" of the wheel is a piece of pipe with an OD
of 1.67 inches. The first turn of wire touches this
hub, and the outer turn of wire is roughly 31 inches
in diameter. Before I wound the coil, I first made
pencil marks every 1/3" along the dowels as a spacing
guide. I then wound the coil using a hot glue gun to
secure the wire to the support structure, with the
pencil marks to guide me. The secondary only took
about 4 or 5 hours to build, which is pretty fast for
this sort of thing, I guess. I chose hot glue mostly
because it hardens almost instantly, cutting out
drying time. Hot glue is also relatively clean, easy
to apply, and easy to remove if you make a mistake.

The secondary has an inductance of 610 uH (Wheeler
formula), and a self-capacitance of 25 pF (back
calculated from an observed frequency of roughly 1.2
MHz). The primary has a 3.6 nF capacitor and 6.97 uH
of inductance. (My first statement that my capacitor
was 6 nF was incorrect. Sorry.) I calculated the
inductance of the primary using the formula for the
inductance of a single straight wire, as opposed to
the Wheeler formula. My thinking was that the Wheeler
formula would be inaccurate for a single turn of wire,
since it was designed for a coil. I calculate that I
need 17 pF of topload capacitance for proper tuning,
which is the equivalent of 6 inch diameter sphere.
Just for the record, I did most of these calculations
on a custom spreadsheet which I created for this
particular coil.

As for the connections of the coil, you are quite
right that I'm taking my arcs off of the center of the
coil. The outer turn of wire is grounded, just as
Tesla showed on his drawings. I think that since most
of the inductance of the coil is in the outer turns,
it is appropriate for the primary to be right on the
outside of the coil where it can get some decent
coupling. My primary gap is static, and is connected
across the transformer as opposed to the more popular
wiring method with the capacitor across the
transformer. My thinking was that the gap would act as
a safety gap as well, and would protect the
transformer from high frequency by short-circuiting it
right out of the resonating system. The capacitor is a
homemade mica job. I hope that this is enough
information. :-)

-William

--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Barton B. Anderson by way of Terry
> Fritz <twftesla-at-uswest-dot-net>" <tesla123-at-pacbell-dot-net>
> 
> Hi William,
> 
> That truely is an interesting coil. Great job!
> 
> Where do you take spark from? the center of the
> secondary or the outer
> edge? Looking at it, I might try
> winding the primary below the secondary nearer to
> the center and place a 2"
> x whatever diameter toroid
> along the outer edge of the secondary. Just a
> thought. I would image using
> the Archimedes Spiral
> calculation for the secondary. Do you have
> dimensions you could throw our way?
> 
> Take care,
> Bart A.
> 

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