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Re: sync vs. static gap, was 12kV, 30ma TC specs, 42" spark
From: FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
Sent: Wednesday, September 17, 1997 9:01 AM
To: tesla-at-pupman-dot-com
Subject: Re: sync vs. static gap, was 12kV, 30ma TC specs, 42" spark
All,
A few list members asked if a static gap could match the
performance of a synchonous rotary gap on a neon powered
Tesla coil using resonant charging for maximum spark output.
I had obtained results in the past which suggested that the static
gap might come close in performance to the sync gap, but the
comparison had one important flaw; the tests were done using
two different transformers having the same specs. As we know,
some transformers are manufactured more robustly than others,
or have differing leakage reactances.
I happen to know that the 12kV, 30ma neon trannie used in the
original static gap tests was a rather robust model...it may have
been able to put out more current... and this may have allowed it
to give 40" sparks using a static gap.
To avoid this extra variable, I re-did the comparison using the same
(weaker) transformer and Tesla coil. I simply removed the sync-gap,
and installed the vacuum quench static gap in its place. It was
immediately clear that the static gap was a loser in this application.
I had to open the gaps to such a distance, that the transformer often
failed to fire the gaps, and still, max observed spark was 37". But
most of the time, the spark was closer to 28" or so. Unlike the
performance with the sync-gap, the static gap was unable to fire
the gap 120 times per second, instead the gaps fired only 60 times
per second. Occasionally, the gaps gave a burst of 120 bps
firing, and at that time, the spark would reach out to the 37" mark.
During these tests, the safety gaps were set at about 0.25" at each
side of the neon trannie, and they fired occasionally. In general,
the firing of the gap was somewhat unsteady, and the coil sounded
wimpy. I varied the amount of vacuum air, but the results never
improved very much. The static gap BTW is a 6 gap copper
cylinder gap with squirrel cage blower.
In contrast, operation with the sync gap is steady and powerful,
and the sparks leap outwards in bolt-like fashion, and is a wonder
to behold, compared with static gap operation. It is possible that
a smaller cap than .007uF would work better using the static gap,
but I didn't try it. It is also possible that re-adjusting the coupling
and tuning may have helped a little, but I didn't try these either.
In a related experiment, using the sync-gap, I reduced the spacing
of the safety gaps to 0.25" (I usually use 0.375"), and I was able to
turn up the variac to the point where the TC gave 32" before the
safety gaps fired. The 0.25" setting is just wider than the trannie
can fire with no TC connected to it, so only a little resonant charging
should occur. I thought it significant that the system still gave 32"
sparks under this condition. Normal operation at a normal variac
setting and safety gaps set at 0.375 gives 42" sparks.
I suppose that by reducing the safety gap spacing to 0.25" as I did
above, will prolong the life of the neon trannie, although I have not
had any transformer failures since I've been using the sync-gaps.
I suspect that the use of a sync-gap allows a much higher voltage
to be drawn from the trannie without destruction due to the steady
firing nature of the sync-gap. Only time will tell how long the trannie
will survive. Skip Greiner who uses a similar sync-gap along with
resonant charging has also had no failures of his neon trannies.
Perhaps others will do their own comparisons of static vs. sync-gaps
in resonant charging neon powered coils. It is possible that my static
gap is not the best.
It would be quite intriquing if it is found that the use of a sync-gap
does indeed allow for the use of optimal resonant charging, and
maximum spark output from a neon powered system, without
premature transformer destruction.
Regards,
John Freau