Re: MMC Capacitors, Spark Gap Phasing

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>

In a message dated 12/10/00 2:43:19 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

> I am new to this list, but am determined to begin construction (with my
>  son's help) on my first coil in the New Year. After much research I have
>  decided to use the "MMC" style capacitor bank. I am wondering if anyone
>  else has bulk quantities available (this was prompted by a previous
>  poster who indicated he had sold out). I can get them through an
>  electronics wholesaler but they still seem high at 1.40 Canadian. I am
>  also hoping that someone can explain "phasing" as it relates to rotary
>  spark gaps. I have an electrical background but I am (so far) not
>  grasping the concept. This list is a great resource, thanks to all the
>  informative posters!

S, all,

Welcome to this wonderful list.  MMC's are an excellent choice.

Phasing of rotary gaps becomes most important when running a 
synchronous rotary gap.  When the gap is phased properly, the
gap will fire when the cap is fully charged for 120 breaks per second
operation.  For 240 bps, the phase should be adjusted so that the
the cap has equal energy for both firings in each ac half cycle.  If the
gap is not phased correctly, the gap may fire when there's only a
little voltage on the capacitor, and the output sparks will be very weak
or even non-existant.  Sync gaps running at 120 bps are excellent
for use with neon sign transformers.  Sync gap running at 120 bps
are excellent for any coil, provided that the tank capacitor is of the
proper size.  I run all my coils at 120 bps synchronous now because
of the greater efficiency it provides. 

For non-sync rotaries, phasing is basically not important.  The firing
points will run along the 60Hz AC sine wave, and fire wherever they
can.  Whenever the voltage is high enough to fire the gap that is.  
Some firings will be skipped, although electrode presentations
occur at that point.  There will be certain rotary speeds however that
cause an undesirable pulsing or surging of the sparks.  This occurs
when the break-rate comes close to the sync break-rate.  Since
non-sync gaps are usually variable speed types, this is not a problem.
Simply select a speed that does not surge.  Non-sync gaps should
not be used with neon sign transformers though  (you can do it, but
the xfrmers need a lot of protection and will not be that efficient).

I've added a schematic at my website for my new simple convenient 
sync phase remote control.  There's also some simplified theory at
the site, and photos of my efficient TT-42 coil, etc.

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

John Freau