Hi Bart,
Full energy transfer occurs at the first notch. So if you quench at
the first
notch, that's the ideal time to quench. If it takes 6 half cycles to
do a full
energy transfer, then the first notch will be at the 6 half cycle
point. I'm
saying that the gap will never quench at the 3rd half cycle which would
be at a point well before the first notch. I'm saying the coil will
never
quench before the 1st notch, unless a ground stike happens maybe,
but that's a special case. Usually small coils quench at the 3rd notch
or so. This 3rd notch is not before the 1st notch, it's well after that
time. Now let's look at how many half cycles occur by the 4rd notch
for a poor quench situation.
If there are 6 half cycles to the first notch, then there are 18 half
cycles to
the 2nd notch, and 30 half cycles to the 3rd notch, and 42 half cycles to
the 4th notch. Now if the coil runs at 100kHz, then each half cycle is
5uS. Now assume a poor quench at 4th notch. 5uS x 42 half cycles
= 210uS. This is a considerably longer duration than the 30uS duration
to the 1st notch.
In the example you gave of the 50hHz coil, it's true the full energy
transfer would occur in 63uS. But why do you think the gap would
quench at that time or earlier if it's a poor quenching gap. Only
the best gap might possibly quench at that 63uS which is also the
first notc
h. But if that coil has poor quenching, then it wil quench
much later than the time of full energy transfer. When this happens,
some energy comes back from the secondary to the primary and
keeps the gap lighted, then transfers back to the secondary and
keeps making these round trips until the gap finally quenches at
perhaps the 4th notch in a poor quench situation. Now at a
4th notch quench, the spark duration is actually 512uS. If the
cap charges in 20.75mS, then the ratio is 40.53. This is about
2.5% which is considerably larger than the 1% charge time that
you mentioned. And this is the point I was making.
Your analysis assumes 1st notch quench or sooner. I'm saying
the quench never occurs before the 1st notch. I'm also
saying that in a poor quench situation, the quench will occur
much later than the 1st notch (perhaps the 4th notch).
Now with a smaller coil that runs at 100kHz, and 300bps,
and assuming the same charge time you mentioned, then
the ratio is 81.06 which is still more than the 1% figure you
mentioned. I agree that the cap charging issue is not a large
factor with the poor quench. Since we want to get the
details right, I wrote this to give the correct math and show
the way to calculate the durations to these various quenching
notch-points (3rd notch, 4th notch, or whatever)
Cheers,
John
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