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Re: Using sync gaps



In a message dated 98-09-29 01:49:44 EDT, you write:

<< 
> John, one question,
> My coil (12.5" x 34.2"), 18awg, etc.. is now using a cap
> size of .06uF = 12.4J. The resonant size cap for this
> coil based on xfrmr impedance of ~20k ohms was 0.128uF.
> This created a bang size of ~25J! Taking the good advice
> of experienced coilers on this list, I halved my cap
> size to prevent "smoke, etc..". Wouldn't you say .06uF
> is a large enough capacitance to provide plenty of
> pudding to the streamers at 120bps? This cap isn't
> matched to the input impedance but are all bets still
> off?
> Bart >>

Bart,

When I said matched, I didn't mean matched for
resonant charging, I just meant matched to maintain a certain 
power input.  What I was really refering to is the situation where
someone has a certain sized cap, it could be .06uF, and they're
running at let's say 300 - 400 BPS, then they keep the same cap,
and install a 120 BPS sync-gap, and are surprised to obtain less
spark output.  They should go to a larger cap of around .12 or a
little more to keep the input power more or less the same as it was.

But if they aren't using very many primary turns to start with, then
when they go to the larger cap, the higher primary currents that
result from the combo of the larger cap, and the fewer turns needed
to tune, may hurt the primary Q, due to gap losses, especially
using narrow secondaries having low inductance.  In a case 
like this, best results from
the sync gap may require a complete TC re-design, including more
inductance in the secondary, to allow more inductance in the primary,
to give a higher tank surge impedance, etc.  The overall design 
should be built in a matched or synergistic way in this sense.

If you were running at let's 200 BPS (calculated) originally, you 
may get (about) the same spark length using the sync gap, even 
keeping the .06uF cap, because a 200 BPS system run on 60Hz
AC will actually fire somewhat fewer than 200 times per second 
since the gap won't fire when the electrodes present too low on 
the AC sine wave.  But if you're running at 300 - 400 BPS or so, 
then I would think that you'd need a larger cap than .06uF to maintain 
the same spark length when you go to the 120 BPS sync gap.  In 
any case, a lot of coils use a .128uF cap without anything smoking,
but the components do need to be beefy enough to handle the currents.

I have not tested any sync gaps above 2kW input however, I 
unfortunately don't have the room   :(

John Freau