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

[Ken or Doris Herrick]

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?

KCH

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.
>
> Steve
>
> On Thu, Nov 12, 2009 at 10:57 AM, Ken or Doris Herrick <kchdlh at sonic.net>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
>>
>> [snipped]
>>
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