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Re: Twin coils - PSpice model development



Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:

 > Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
<Rscopper-at-aol-dot-com>

 > PSpice output:
 > 
<http://www.hot-streamer-dot-com/rscopper/trace1.bmp>http://www.hot-streamer-dot-com/rscopper/trace1.bmp
 > output with shorted secondaries:
 > 
<http://www.hot-streamer-dot-com/rscopper/trace1.bmp>http://www.hot-streamer-dot-com/rscopper/trace1.bmp

You sent the same trace two times.

 > What is missing is the coupling between secondaries.  That's why I was
 > asking for some actual measurements vs. calculated values.

This would make just a small change. My program, and the others, still
don't calculate coupling between coils with a lateral spacing. This is
easy to implement numerically, but I suspect that analytical solution
is not possible. I will take a look when I have time.

 > Many twin
 > systems have been built, but I don't think they have been studied as well
 > as they could. It's difficult to operate coils as large as my Twins and
 > take measurements (in my front yard anyway).  I don't have a table-top twin
 > system to experiment with (yet...)

Many important details can be observed by exciting the circuit at low
power, with the gap replaced by a low-impedance square wave generator,
and observing the transient waveforms directly in an oscilloscope. The
high-voltage waveforms are basically just scaled up versions.

 > I don't think a bipolar coil arrangement has the same variables as a twin
 > system either because of interactivity due to proximity and transmision
 > line characteristics.

A bipolar coil (one primary, one secondary with balanced output) is
essentially identical to a conventional Tesla coil. The capacitive
loading of the secondary coil is composed by two grounded capacitors,
one at each side of the secondary. The lumped model has only two
resonances, and a possible DC common-mode voltage at the secondary
outputs (a 5th-order system).
A Twin coil (two primaries, two secondaries) is a 6th-order system
(3 resonances) that reduces to 4th-order (2 resonances) when it is
perfectly symmetrical.
If the center of the secondary coil in a bipolar system is grounded,
it is also a 6th-order system, because the currents at the two
sides of the secondary (lumped) are not restrained to be equal, and
the outputs can't anymore sustain a DC voltage.

Transmission line effects in these system are measurable, but have
little effect in the regular operation, that is adequately modeled
by a lumped model. The main reason for this is that with the use
of top loads significantly larger than the "self-capacitances"
of the secondary coils, the main resonances are far below the first
"transmission line resonance", that is at about 3 times the first
frequency where the secondary coils resonate, without top load.
Add to this large frequency difference the increased losses at higher
frequencies, and the high-order resonances become barely observable.

 > As we build Gemini, the more we understand the system, the easier it will
 > be to optimize and tune it.

I would tune a twin at low power, first adjusting the symmetry
by observing both outputs, and then tuning the primary to obtain
perfect notches at the primary voltage. Iterating this procedure
a few times, it is also possible to adjust the system to one
of the modes of optimal energy transfer.

Antonio Carlos M. de Queiroz