Re: Spark Gap Question

[FutureT-at-xxxxxxx (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

In a message dated 11/25/00 10:44:05 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

> Original poster: stanmoore-at-mindspring-dot-com 
>  
>  What is the advantage of a rotary spark gap versus the traditional spark 
gap?
>  
>  Can a rotary be used with a 15kv/30 ma NST?
>   
>  Thanks,
>   
>  Stan

Stan,

A rotary will not automatically give any advantage, it all depends
on the coil system parameters.  If you're using a small capacitor,
which is STR sized, and the coil is a small low powered one, a
rotary may give no advantage.  Often a large coil works better with
a rotary because a static gap may fail to quench unless it is
carefully made, and supplied with good air flow for cooling and
quenching.  When using a small LTR system, a synchronous
120 bps rotary may improve the coil's efficiency.  I've found the
best efficiency at low break rates, along with a sync gap, but it is 
imperative that the capacitor is the correct size for best results.

I use 120 bps synchronous rotaries for both NST and PT 
powered coils, and have obtained the best results this way.

An advantage of non-sync rotaries is that the breakrate can be
easily changed by varying the motor speed.  When using a static
gap, the breakrate can be changed only by changing the gap
spacing, the capacitor size, or the input voltage.  However, the
efficiency of a non-sync rotary is generally lower than a 120 bps 
sync gap system (assuming they are both optimally designed).

There is an old myth that rotaries quench by stretching and 
breaking the spark.  This does not occur, rather the the gap
quenches after the system runs out of energy from a bang.
Basically, rotaries fire based on timing, not on voltage.  Static gaps
fire based on voltage, not on timing.  

Yes, a rotary can be used with a 15/30 NST, but it should be a sync
rotary.  Non-sync rotaries tend to destroy NST's unless many 
precautions are taken.

One of my coils uses a sync rotary with a 12/30 NST and gives
42" sparks.  This coil, and some theory, etc., can be seen at my
website at:

         http://hometown.aol-dot-com/futuret/page3.html

John Freau