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Re: Rotary Gap Experiments

Tesla List wrote:
> 
> Subscriber: FutureT-at-aol-dot-com Tue Dec 31 22:58:29 1996
> Date: Tue, 31 Dec 1996 15:49:53 -0500
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Rotary Gap Experiments
> 
> Bert, All,
> 
> Bert, enjoyed your project article in the new TCBA  News--nice construction.

Thanks. This was my earlier 6" coil, which I could never drive over k=
0.153 without it getting flashovers. It did deliver up to 48"
point-to-point arcs though. In June. I went to a bigger primary and the
10" Behr Build50-insulated secondary with a larger toroid. I now run at
about k=0.21 with _no_ evidence of corona or flashover.

>  You mentioned that you were interested in various rotary gap designs.
>  Here's a description of some additional rotary work I did a couple of years
> ago:
> 
> 1)  Synchronous gap:  Used 8 spinning electrodes, 2 fixed electrodes.  The 8
> spinning electodes were bunched into two clusters.  Because these clusters
> centered closely around the peak of the AC sine-wave, EVERY GAP PRESENTATION
> ACTUALLY FIRED  (this was verified by o-scope).   The net result of this
> design was that the TC output and behavior was identical to a traditional
> synchronous gap which had perhaps 10 or 12 EQUALLY SPACED electrodes (no
> clustering), since in this case firing would not occur on every gap
> presentation since voltage would be too low at some presentations (the ones
> that occur at a low point on the AC sine wave).  Only advantage I see in the
> clustered design is that fewer electrodes are needed, less drilling, etc.
>  Disadvantage is you need a greater range of phase adjustment on the rotary
> for initial phasing adjustment.

Interesting approach! Until now I'd been only considering equally spaced
electrodes on the rotary.

> 
> 2)  Synchronous gap:  Same as above, but the spacing of electrodes within
> each cluster was varied such that electrodes near the center of the clusters
> were spaced closely whereas electrodes farther from the cluster center were
> spaced farther apart.  The plan here was to give the capacitor more time to
> charge when AC voltage was at low points on the sine-wave, but less time to
> charge when AC voltage was at a high point (peak) of AC cycle.  The result
> was that the capacitor WOULD NOT have time to charge fully at the AC cycle
> peak, but would charge fully at lower points along the AC sine wave.
>       The overall result of this design, was that each of the 8 firings of
> the rotary occured at the same voltage level.  In this sense, the system was
> like a DC powered system, but without the complexity of a DC power supply.
>  (an o-scope was used to verify that all the gaps fired at the same voltage
> level--they either all fired, or none fired.  In a normal rotary, more
> presentations fire as the input voltage is increased--at least if you're
> using external series gaps).  Of course this technique (firing at same
> voltage level) limits the available power of the system since the peak energy
> is never utilized, but this is easily compensated for by using a main
> transformer of a proportionately higher voltage capability.
>       This technique may be very useful for precisely controlling dwell and
> quenching.
> 

This is a very interesting and more sophisticated approach! This might
also be a good way to make other measurements on the coil since "bang"
size would be more equal. I'd never thought of doing this either! 

> 3)  Non-synchronous gap:  Used 8 spinning electrodes, 4 fixed electrodes,
> 2500 RPM, about 650 BPS.  Of the 8 spinning electrodes, 6 were spaced
> equally, but 2 were not--they had a greater spacing from the previous
> electrodes.  The gap was symetrical however.  This arrangement seemed to give
> a longer spark as compared with a rotary with equal spacing between all 8
> electrodes.  The occasional greater spacing may have allowed the capacitor to
> charge, at that point, to a higher voltage thereby giving out a tremendous
> spark burst.  I suspect this is what was happening, because the sparks were
> not consistantly long, but instead, a long spark was thrown out every few
> seconds--corresponding perhaps to the coincidence of the wide electrode
> spacing and the peak of the AC cycle.  The thing I liked about the system,
> was that the occasional long sparks, when they occured, were psychologically
> surprising to one's mind, making the display more exciting, at least to me.
> 

This is _another) interesting variation that I hadn't thought of!! NEAT
idea!!

> Happy New Year--And Happy (and safe) Coiling!!!
> 
> John Freau

Thanks for the overview, John, and especially for the non-linear
thinking (and gap design) approaches. Excellent!!

Safe coilin' to ya, and Happy New Year!

-- Bert