Re: MOT Coil operational notes

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

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

In a message dated 12/2/02 11:38:24 PM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:


>Also, I watched the rotary with some welding goggles. Before the
>static gap in series, I was getting pretty bad follow round, ie the
>arc was present for quite some time after each presentation. These
>arcs were big flamy orange things. With the airblast in series, the
>follow round stopped, and the arcs were white.


Greg,

This sounds like re-firing and/or power arcing.  I've seen this happen
with low L ballasting.  Often asrsg's need to have only a small
amount of ballasting, and this can cause power arcing or perhaps
refiring.  The series static gap may stop the power arcing, and also
the refiring.  There may be perhaps other
explanations.  The whole issue is not discussed often.  The follow-
around you saw may be the result of re-firing with subsequent
power-arcing maybe.



>So, in conclusion, for a given "ringing" tank circuit, a low quench
>time may not be that important, provided it is not ridiculously high
>(which I feel that 450uS may be). BUT, the low quench time may reduce
>the shorting of the transformer, reducing current draw and allowing
>the use of a bigger tank cap for more spark.


There's no doubt that a too-long quench time is bad, and that power-arcing
is very bad.  A faster quench lets the cap begin to charge sooner, and
thereby permits more power throughput through the system.  Yes,
450uS does seem extremely long and will probably result in re-firing.
Static gaps can stop the re-firing because the slightly recharged cap does
not have enough voltage to fire across both the rotary and static gap.
Using a larger cap should tend to prevent refiring, and may make
the static gaps unnecessary in some systems.  Simply widening
the rotary gap spacing may help too.

I've also had many problems when I tried slowing down a rotary
too much, due to long dwell times.  I do prefer short dwell times
and fast quenching.

John


>Cheers,
>
>Greg.
>