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Re: [TCML] Re: Spark gap Resistance
Chris is trying to quench faster by using a fast rotary. That won't
happen
because the quench is not controlled by the mechanical dwell time.
The spark at the gap will arc before the electrodes line up, and stretch
out if needed after the electrodes pull apart.
I agree totally. I have close up images somewhere (poor quality of course!)
showing the spark gap contacts burnt up. The gap has burnt up just before
actual alignment, though there is nothing after. If the gaps were spaced
wider then the "pre-arc" would be less though tricky to get exact. IMHO the
RSG dwell time is probably twice for actual spark dwell time..
To really stretch the spark
and force the quench would require a rotary gap construction well beyond
what anyone has tried.
Exactly my point, noboby has tried it (hope to build one myself next year)
Generally rotaries are more for timing when the
spark occurs rather than for quenching purposes. Quenching is more
about draining the energy out of the system quickly. For the most part,
air streamers don't drain the energy that quickly, and that's the main
problem preventing a fast quench.
Well we have gone full circle again now, as this suggests more current and a
higher frequency will drain a lot faster and then quech time is really
un-important as the tank has discharge long before the mechanical time is up
anyway.
In any case, as you said Bart, a fast
quench is not really very important. It's interesting to consider the
various DRSSTC designs and SISG coils which have lower switching
losses. They may be more efficient because of that, but the improvement
is not huge compared to a spark gap coil. This shows that the gap
losses
(at least the part of the gap losses that matter) are not that large.
---
I kept emailing Terry about SISG vs spark gap. To me, I can take for example
500W to produce a 20" spark, but Terry SISG can give 20" at 120watts ? I
really wanted Terry to try a RSG VS SISG experiment to do a direct
comparision, Though he seems to have vanished of late.. That test in itself
should give a really good idea on how much is lost over the gap.. come on
Terry! *pokes with big secondary coil*.....
Were talking about high energy pulse currents. If there is an escape
route, high energy pulse currents will find it.
Yes, when the quench is forced by building a lossy gap, then the gap
wastes
more energy. Since the energy is now used up more quickly, it lets the
gap quench more quickly. But if first notch quenching can be obtained
by using air blasts or something similar but without making the gap
lossy, (and without reducing the coupling) then a benefit may be seen.
Reducing the coupling has a similar effect on spark length, as using a
more
lossy gap. Both waste energy before it can get to the secondary.
I think I understand what you are getting at, though it still does not make
sense that 3 trips back and forth to the secondary is more efficient than 1
single trip. If 1st notch quench is too fast then you could loose 50% of the
tank power. For example if we use loose coupling and take 10 ringdown cycles
to the first notch then all is good. If we miss one or 2 cycles even due to
quench times then it really does not matter to much...... however....
If we now take a tight coupling and energy ringsdown in 3 cycles and we aim
for 1st notch, we could be 2 cycles out still and the gap could quench after
the first cycle and we may only get 20% of the tank energy transferred. If
we are 2 cycles to slow then we probably quench half way though the second
notch, again wasting energy.
It suggests a low coupling factor would be best as the quench time is less
important then.. transfer the energy over 10 cycles then if you quench 2
cycles either side then it really does not matter. It also suggests a lower
frequency would be better as the overall cycle time would be a lot longer.
So instead of 10 cycles at 100khz you could have 20 cycles over 50khz. Which
makes the dwell time pretty much zero effect on efficiency.
All that being said, I know I tried a very low coupling of just that years
ago. There was about 12" gap between primary and secondary, maybe more..
coil ran very poor! To be expected I guess. Though if the transfer was 30
cycles then it should reduce RSG times even more (the figure becomes
pointless). Though as I stated, where did all the tank energy go ? I suspect
that the spark gap was in conduction for such a long time that if it looses
just 1% over 20 cycles, then it is a 20% loss overall.
It suggests the spark is actually very efficient, maybe dare I say 99%.. but
if you run the spark gap for 100uS or 500uS then over that time you will
loose more tank energy. So then you come full circle again back to it would
be far better to push the tank energy as fast as possible using high
currents and high frequency. Then you are back to quench problems. I also
think higher frequency will conduct better across the gap also reducing
spark gap losses even more. Though could be very hard to build a RSG of a
good enough spec in order to make the entire system work correctly..
Its a long ponder of mine that all these factors just force everyone to use
a lower frequency in effect to make up for other losses/design problems
elsewhere in the system. I also wonder if this is the reason nobody seems to
have had any luck with high Q coils as you just can't place a high Q coil in
place and expect it to work better as it just won't work without a total
system overhaul...
Chris
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