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Re: [TCML] Capacitor for the 10 in. coil

Hi Carl,

BPS are breaks per second or bangs per second - the rate that the gap fires in a SGTC. If the break rate is too low, the secondary spark channels (leaders) fully cool between firings, and each spark becomes an independent event instead of building upon residual conductive paths blazed by previous bangs. The result is a sequence of independent short sparks that dart in all directions instead of longer growing hot sparks. In still air, spark growth from bang to bang requires a break rate of at least 80 BPS or so. Maximum spark growth is achieved once the BPS is around 400 BPS or so.

Further increases above 400 BPS tend to increase output power (which is proportional to break rate), and although the leaders do not get longer, they do become whiter and brighter. At low break rates (particularly at 100-120 BPS from synchronous gaps operating from 50 or 60 Hz sources), sparks appear to be long and "lazy", moving slowly upward from thermal effects or light breezes. Higher break rates seem to induce more "frantic" behavior, particularly with the smaller, outermost branches. Since low break rates also reduce average output power, low BPS sparks tend to be thinner and bluish-purple in color instead of the hotter, white color seen in higher BPS/higher power coils.

If your coil is operating at only 30 BPS, you may need to increase the output current from your HV power supply or reduce the main gap length so that it can sing and "project" properly... ;^)

Bert Hickman
Stoneridge Engineering
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books

Carl Noggle wrote:

What does the acronym BPS stand for?  I assume it's not the actual pulse
repetition frequency, since for 480 BPS that would be about B above
middle C.  My poor little coil is a relative piker, only running at
about 30 ragged pps (blown gap).

Thanks for clearing up the confusion---


Hi all,
     The capacitor for the big coil is a Maxwell MMC.  There are 5
strings of 2 for a cap. of 76.4 nf.  They are the 37767 caps at 35 kv
and 30nf.  They were all purchased used from e-bay.  Very easy to
integrate into the coil.  After an 8 minute run I could barely feel
any warmth coming off of the bank.  The cap is connected with .125
flat ribbon copper that is 1" wide.  Cap is in series with primary.
     At John IV,
you wrote,
:Excuse me,
:That last message should be for Jason. My apologies for mis-typing
your name.

   Thats cool.  You can call me a fellow coiler.  I really like the
effect your sparkgap gives in those tests on youtube.  How much power
have you ran through that gap??   Anyway lets see if I can give some
more info on my coil :  It is powered by a 12470/240  sec/pri rated
10kva.  I am not sure what actual current is, but will be putting amp
and volt meters in the control panel.  It is ballasted by two cores
out of a Lincoln 250 that are rewound with a gap cut and shimmed with
PC.  The transformer has a tap setting on the side and it is set at
105%.  The sparkgap motor is  1 1/2 hp  3600rpm.  There are 8
electrodes that are .5 in. brass threaded rod.  The stationary
electrodes are 1/2 copper studs out of a giant starter.  Ballast L is
8.89mh on the primary side of the pig.      I have ran the coil for
about 3 hours all together with runtimes of about 4-5 min average.  2
days ago I let it go for about 9 minutes as I got everything in tune.
No warming of the caps this time as previous runs were at 720bps.  I
just finished the new sparkgap plate last wednesday  to reduce heating
in the caps by lowering to 480bps.  They (the caps) are only rated 500
pps, so best not to overdrive them to much.      It seems the coil is
constantly changing as I make improvements (well, sometimes they are
improvents, other times....).  I would be glad to answer any questions
from all.
working on new topload
Jason in S.D. _______________________________________________
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