magnifiers, BPS, etc

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

Original poster: "Mr Gregory Peters by way of Terry Fritz <twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>

I have come to the following conclusion regarding rotary gaps (see
following question). It is a bit "over the place", but I ask you to read
it entirely before passing judgement. I have only limited experimental
results to back it up however:

Is async (high BPS) or sync (low BPS) better?

Well, before I go into a detailed discussion on gap types, I would like
to present another relevant theory I have about tesla coil operation. I
think the emf produced by the coil has relatively little to do with the
actual spark lengths produced. People often apply the 1MV/metre rule,
however it has been shown that most tesla coils which can arc a metre
are not actually producing 1 million volts. I think this is because the
coil is basically trying to arc through a large ionised "sphere" of air.
This ionised sphere is much easier to arc through than "normal",
unionised air. Therefore lower voltages can arc distances that would
seem to (normally) require higher voltages. Therefore, what would appear
to be most important would not be the actual emf of the coil, but more
its ability to charge as large a sphere of air as possible, or POWER
output. This may explain why above, say, 2kW, you get less and less
spark output for subsequent increases in power input. If you try to
charge a 2m radius sphere as opposed to say, a 1m radius sphere, you are
charging 8 times the volume of  air, which will clearly need ALOT more
power (though probably not 8x more power). Incidently, maybe the arc
lengths produced in a slight breeze (which removes the ionised air) are
a better indication of voltage output. So basically, I think power
throughput, not voltage is more important for bigger sparks. So how does
this relate to RSGs? Well, we need an RSG that will provide the most
POWER, not VOLTAGE to the tank circuit, and now, onto my original theory:

Well, I think async and sync RSGs can both transfer more or less equal
amounts of power to the tank circuit. The sync gap does it with more
energy less often, and the async does it more often with less energy.
Overall I think the power transfer is the same. So why use a much more
complicated sync gap? Well, people have noted that async gaps provide
less spark output for the input power than a sync gap. WHY? I think this
is because the low break rates used in sync gaps provide less "shorting"
periods for the transformer. The async gaps run higher BPS and thus
"short" the transformer more often, increasing the RMS current
transformer draw substantially. However, I think this shorting action
can be reduced substantially by using a DECENT static gap in series with
the rotary. This has two advantages:

Firstly, the arcing periods are shorter, due to better quenching.
Therefore the shorting of the transformer is reduced.

Secondly, a higher voltage can be stored in the capacitors before the
gap fires.

In this way, the rotary is used purely to commutate the spark and
control the BPS, not for quenching. 

I CAN BACK THIS UP WITH MY OWN MEASUREMENTS!!! I placed a decent
airblast gap in series with the async rotary (3kVA coil). The spark
length did not improve by more than a few inches. However, the current
draw dropped to nearly half of its original level.

CONCLUSIONS:

1. Maybe we should have another look at the poor old async gap?
2. How would a sync gap run with a static gap in series?



Greg Peters
Department of Earth Sciences,
University of Queensland, Australia
Phone: 0402 841 677
http://www.geocities-dot-com/gregjpeters