[TCML] Re: Spark gap Resistance
FutureT at aol.com
FutureT at aol.com
Tue Nov 20 09:48:03 MST 2007
In a message dated 11/20/2007 11:00:25 A.M. US Eastern Standard Time,
list at future-technologies.co.uk writes:
><> 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
>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
The energy has to be drained from the secondary via the sparks. It's not
clear to me what heavy primary currents has to do with this.
>>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
>> (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
>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*.....
Terry's coil if it performs as you suggest is a little more efficient than
a spark gap TC. Your coil however is extremely inefficient. You should
get a 38" sparks from 500W with an reasonably efficient spark gap coil.
>> Yes, when the quench is forced by building a lossy gap, then the gap
>> 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
> >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
>tank power. For example if we use loose coupling and take 10 ringdown
>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
>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.
The key to understanding this is that *all* the energy is always transferred
by the first notch no matter what. But some of it comes back to the
primary if quench does not occur. The spark streamer meanwhile utilizes the
portion that it can during the first transfer. Thus a tight coupling gives
sparks, regardless of how good the quench is (assuming no power arcing).
>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.
>makes the dwell time pretty much zero effect on efficiency.
See above. You're assuming that if the coupling is too tight that full
transfer does not occur by the first notch, but it does. The energy just
doesn't *remain* in the secondary (it goes back to the primary).
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.
Loose coupling causes the spark gap to remain firing for a long time
*before* the first notch. That is bad because losses are continually
occuring during that time. This is where the energy is lost, and is why
loose coupling is bad.
>It suggests the spark is actually very efficient, maybe dare I say 99%..
>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..
See my other email about the square root frequency relationship with
inductance, regarding the losses.
>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
>have had any luck with high Q coils as you just can't place a high Q coil
>place and expect it to work better as it just won't work without a total
The secondaries in our coils tend to be high Q. Of course when they
start sparking it slashes the Q.
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