Rotary Gaps

 * Original msg to: Scotty-at-wesnet-dot-com
 * Carbons sent to: usa-tesla-at-usa-dot-net

Quoting Scott Myers <scotty-at-wesnet-dot-com>:

> Have you done any research on make/break ratios of rotary gaps. 
> There is obviously a ratio when looking at the width of the 
> electrode ~vs~ the space in between.  I suppose that what is 
> important is the charging/discharging times as the electrodes 
> pass one another.  Of course, theoretical is always different 
> from practical.

> Experimenting with this would get time consuming and expensive
> as you would have to build rotarty gaps of different diameters
> with different electrode diameters.  Have you, or perhaps 
> someone in Hull's group, looked at this in the past?

I guess what you are referring to is a combination of "dwell"
time and break rate. The dwell is the actual period of time that
a particular gap fires. I have seen adjustable rotaries where the
motor speed and dwell time both were adjustable. The conclusion
that I come to when seeing these gaps in operation is that the
shorter the dwell times, the better the coil performance.

For this reason it would seen advisable to avoid large diameter
electrodes for the rotor and stationary gaps on the rotary unit.
The large diameters mean that the electrodes are in close
proximity for an extended period of time as they move past each
other, thus creating a large dwell. Very small electrodes would
create a resitance bottleneck, so some "happy medium" should be

The early pulse modulators on some WWII radar systems employed
rotary gaps. The federal government did some extensive
experimentaion with rotary gaps and the results were published:
by G.N. Glasoe and J.V. Lebacqz, 1948, McGraw-Hill. The experi-
mental data may be found in Chapter 8, "Switches for Line-Type 
Pulsers; the rotary spark gap" pp 275-335. Photos, drawings, and
specifications of WWII rotary spark gaps appear on pages 287-293
and 448-454. 

Having actually seen a rotor for one of these early pulse
modulators I can tell you that the stationary electrode was wide
and flat, like a tongue depressor. This electrode could rotate to
present a different aspect to the moving rotor, and thereby
adjust the dwell time. When the moving electrode went past the
stationary, and the stationary electrode was turned to present
the flat surface, the dwell time was lengthened. When the
stationary electrode was turned to present the thin edge, the
resulting dwell time was much shorter.

Having seen the same rotor in operation on a Tesla coil I can say
that the shorter dwell times produced a better ouput from the

Richard Quick

... If all else fails... Throw another megavolt across it!
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