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Re: Re: [TCML] Solid state efficiency, was: mini Tesla coil specs

Steve (& all)-

Would not the "racing spark" condition be caused by harmonic-excitation due to the very hight rate-of-rise in a SG-type of coil? That fast leading edge would "contain" a lot of harmonic energy, I'd think. And with a s.s. coil, it's just not there since the excitation is essentially a sine wave--or perhaps a triangular wave.

I'm envious of your 45" per 11" tall spark! The best I got was perhaps 36" per 36" tall (x 12" diameter). But I don't know if I can agree about a slow rise: as soon as the toroid starts to break out, its capability for storing more charge severely diminishes. How is one to cram in more charge without getting ahead of that breakout?


Steve Ward wrote:
Hi Ken,

It sounds like our intuitions about spark growth agree.  I convinced myself
that the faster energy rise was better because you spent less time wasting
energy making little corona on the rising edge of the voltage rise.  What
led me to believe this was that the secondary voltage in my comparison test
was essentially the same (simulated, not measured), and the spark length was
the same, but it took less time (and thus energy) to make the spark.  I
doubt that our resonator drivers will ever be "too fast" for spark
propagation.  One thing to watch for would be exciting those nasty
transmission line modes on the secondary, which seem to cause the racing
sparks, etc...  Interestingly, i believe it is because the SS excitation of
the system is "slow", that you can build small DRSSTCs that really put out
huge sparks with out much fuss.  Some small coils have produced spark
lengths exceeding 5X the secondary winding length, my best has been about 4X
getting 45" sparks from an 11" tall secondary winding.  This is something
ive never seen with a SGTC, usually racing sparks would just destroy the
secondary if you attempted to cram that much power into one.


On Thu, Nov 12, 2009 at 10:57 AM, Ken or Doris Herrick <kchdlh@xxxxxxxxx>wrote:

Steve Ward writes, "[I] think energy transfer time to the spark is very
important" for maximizing spark length.  I agree and repeat here an opinion
I posted a few years ago:  As compared to a solid-state coil, the relatively
much-higher rate-of-rise of the initial half or whole cycle from the abrupt
shot of energy thru a spark-gap will allow charge to be crammed onto the top
electrode before the spark has a chance to proceed very far.  A research
paper I have a copy of has found spark propagation in air, measured over 1
inch of distance, to require about 50 ns of time.  That extrapolates to
about 20 inches of travel per microsecond.  So with a high rate of
voltage-rise, more charge can be applied to the electrode than can bleed off
through the spark during its first several inches of travel.
Ken Herrick


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