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Re: Dwell time, etc

Original poster: FutureT@xxxxxxx In a message dated 4/3/06 1:26:06 PM Eastern Daylight Time, tesla@xxxxxxxxxx writes: 




> Original poster: FutureT@xxxxxxx

> I did some tests and compared the spark length using a sync rotary,
> compared to a triggered sync static gap.  The triggered sync static
> cap had about a 5/8" spacing.  Yet the coil gave the same spark
> length as when using the rotary.  It's possible the voltage
> was able to go higher using the triggered rotary.

if you accept the possibility of not equal firing voltages, then since
both gaps were sync your coil drew not the same amount of watts in
both cases, so probably we better drop these results? have you
monitored the power consumption during the tests?



I don't have any written record, so I'm not sure.


i guess you didn`t.


btw - i didn`t think that you can use output spark lenght as indicator
of sg losses, not so straight at least or at least not for sg`s of
different types.



Well the break rate was the same with both gap types, and the
sparks looked the same by eye at least.  But I agree it is not
a perfect comparison.  Often we take what we get, it gives us
clues... ideas for further research if nothing else.  The world
is not perfect.  I wanted to check the input voltage and power,
but I may have forgot.  Can't be sure.  Many others tried the
triggered sync gap back then also.  I guess no one else did
the voltage or power comparison either.



> In still another test, I ran my TT-42 coil with a 2 gap series
> rotary, and then added 2 more gaps to make it a 4 gap series rotary.
> The spark length was the same in either case.

when you increase the number of gaps N times, wouldn`t they break at a
shorter _individual_ distance, such that lenght of a total gap wouldn`t
increase N times too, but instead say only N/2 times (or even smaller)?
if so, then you can do this _within reasonable limits_ with no harm,
trying to increase "gap opening speed" for example?



It would seem that way in theory.  I'm not sure if the gap
behaves exactly that way.



>>series rotary doesn`t decrease the dwell time, right?

> Not for small or medium coils.  Possibly for very large coils.

i mean mechanical dwell time (sorry for inaccurate speaking).

>>you want to say, that this gap system is nonsense and just waste of
>>materials and power, and it can be done in _much_ smaller volume with
>>absolutely same performance, coz "opening speed" have no significance
>>at all?

> You must have missed the part in one of my recent posts in which
> I mentioned Greg's coil.

no, i`m monitoring your posts rather carefully (both in the past and
the present), i just can`t agree with that part of the post and want
to discuss more if possible.



Horasho.... OK.


> I agreed with Greg that his series rotary may be helping his
> quenching because he has a large coil. This permits the mechanical
> dwell time to be similar to the actual optimal quench time.  It is
> only under such conditions that the opening time becomes important.
> Also at very high powers it may be harder to quench, so such opening
> speed may become a factor.

can you describe what do you mean saying "quenching" in this case
_exactly_?



I meant preventing re-ignition by an energy transfer.


if you mean quenching the _arc_ "by pulling out and stretching", then
everybody knows that this is just impossible - no matter how big the
coil is. look for example at the jacobs ladder, and jacobs ladder
don`t produce "2800a peak".

so you probably mean quenching the gap itself, i.e. don`t allowing it
to reignite either because of energy left in the system, or from too
fast recahrging of primary cap?
if so, then you are probably assuming that his _arc_ will start to
quench not "before the electrodes even line up" but rather when "the
elecrodes pass each other by", so he can benefit from "fast gap opening"?

let`s see the probability of such scenario in real life.
the gap will start to break not when the electrodes are fully aligned -
sooner, probably at a distance about of one gap electrode thickness
(the gaps were both flat - stationary and flying ones), or even
sooner. electrode thickness was 6.35mm and even at full speed flying
one can pass only 8.56mm in time equal of full transfer time, so at
the end of first transfer electrodes would be practically fully
aligned. then this "fast gap opening" just can`t assist in first notch
quenching.



There may be a delay in the gap breakdown due to the air swirling around in
that area.  I'm not sure.


how about a second notch? at that time electrodes would be probably
far away from each other (but maybe still not far enough - depends on
the energy in the system at that time), but during the first notch
energy in primary was decreasing, during the second notch energy in
primary would be _increasing_, so quenching at the end of the second
notch would be much more harder than on the end of the first one.
do you remember Malcolm talking about nasty _voltage_ transients when
he tried to force a quench after the first notch?



The 2nd transfer to the secondary would need to complete
and maybe he's preventing the 3rd transfer.  I didn't do the calcs for
his coil.  I was just going by what Greg said.  But Ed Wingate
obtains quenching on the 1st notch at full power on his magnifier.
Perhaps Greg's coil can also obtain a quench on the first notch.
In that case the gap should not be too critical provided it doesn't
get too hot (the electrodes).  It's very possible that the main
benefits of Greg's 8 series gaps is too keep them cool and
prevent erosion since the coil is located in a remote area (from
our vantage point in the USA anyhow).  During the initial tuning
of the coil, the sparks may have been weak.  This would have
made the gaps run hotter and may have made it seem that
a more elaborate gap system was needed than was actually needed.
It's possible that a much smaller simpler gap setup would do
the job especially when the coil is well-tuned and running at
full power.  Who knows?


so imo "total mechanical dwell time comparable to a single beat
envelope" can`t assist in quenching even at the second notch - maybe
only at third one.
but then what is the point again in such high speed "fast gap opening"?
third notch quenching is the regular event in all other coils.
it`s seems that only decent spark loading can really quench at all.



You may be correct that the fast opening doesn't really help even in
large coils.


as for 8 electrodes in series - probably somewhere in the end of '96
Greg had been spoken about some of his rules of the thumb - 5kv at one
gap maximum, to facilitate disconnection. 5*8=40kv - compare this with
"Final primary charge voltage - 44kVDC (max)".



I have my own rules of thumb.  I use two gaps for up to 30kV.
Maybe things need to change at higher powers.  I have no idea.

In any case it's good that you challenge and question things.  It
prevents bad myths from developing.



p.s.
how about "that Dave Sharpe optowattmeter!" that you want to build
many times in the past - did you solder the thing finally? : )
i wanted to build it too recently, but then suddently realized that i
just wouldn`t be able to calibrate it properly, coz i don`t have a true
rms ammeter and voltmeter with high enough accuracy at hand, so it
would be absolutely useless % )))



I became very lazy.  Also I have a electrodynamic wattmeter which
seems good enough for my purposes.

John



-----
... If all else fails... Connect another (better if it would be brand
new : D) storage scope across it! : )