Re: [TCML] Re: Spark gap Resistance

[FutureT@xxxxxxx]

In a message dated 11/20/2007 11:00:25 A.M. US Eastern Standard Time,  
list@xxxxxxxxxxxxxxxxxxxxxxxxx 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 
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.
Chris,
 
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 
>>  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*.....

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 
>> 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.
 
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 
longer
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. 
Which 
>makes the dwell time pretty much zero effect  on efficiency.
 
See above.  You're assuming that if the coupling is too tight that  full 
energy
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%.. 
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..
 
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 
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...
 
The secondaries in our coils tend to be high Q.  Of course when  they
start sparking it slashes the Q.
 
John

>Chris






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