Re: MOT Coil operational notes

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

Original poster: "Gregory Peters by way of Terry Fritz <twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>

John and Ted, (and all you other guys) :)

Firstly, Ted, I didn't say 10 uS, I said some TENS of uS. John has
just mentioned that quenching may not be as critical as believed by
the corums, but here is my 2 cents, as usual, based only on my
observations and limited grasp on the subject :)

1. As John mentioned, your gap may be refiring at the low BPS
settings.

2. Despite Johns comments, I feel that 450uS dwell time is too much.
Looking at some of the good designs on the web, such as Bill Wysocks,
they use gaps with a dwell time of about 100uS, which I feel is about
the optimum. It may be true that a lower dwell time does not aid the
output of a given system, with a set tank cap size, but see below.

3. I too have found that a static gap in series with a SRSG was
ABSOLUTELY USELESS!. It was darn near impossible to make the gap fire
reliably, and when it did, performance was poor, so I concur there.
As I mentioned, I feel that low quench times are not as critical with
SRSGs anyway. I was using a variable phase controller, so the phase
setting was good.

4. I found that a static gap in series with an ASRSG was fantastic.
For some reason, I had no trouble making the gap fire at all, even
with only 11kV input. While the spark length did not vastly improve,
if at all, the current draw from the mains dropped to nearly 2/3! So
the efficiency was greatly improved. I feel that this is simply due
to a lower quench time causing a reduced shorting action on the
transformer. I could then have increased the cap size for better
performance, spark wise.

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.


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.

Cheers,

Greg.