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

[Ken or Doris Herrick]

That's very interesting.  I think, seeing that, that my much lower rep. 
rate is what allowed the sparks to jump around the toroid randomly 
rather than sticking to one spot.  I rather prefer that effect & so, 
if&when I get the new one to work, will stick with it for that reason.

BTW for anyone interested, the input ckt I posted at 
http://drop.io/kch_ring_brg appears now to be overkill.  From further 
simulation, it seems I will not need the phase-shifting cap., the 
decoupling circuit, the "pilot oscillator" or the clamping.  Just 2 
pairs of fast diodes, in anti-parallel, across TX1's primary & then 
depend on R3 to limit the Schmitt's input current.  In the simulation 
there's enough energy in the 1st 1/4 cycle of secondary current to start 
the feedback-ball rolling.  Using that scheme, simulation of 1/3 of my 
ultimate primary ckt (since my freebie v. of the program won't allow for 
all of it) shows that a) the (untuned) t.c.'s primary current becomes 
close to a sine wave after 20 cycles or so and b) switching occurs at 
nearly current-zero-crossing.  Just maybe I won't be zapping quite so 
many transistors this time...

KCH

Bert Hickman wrote:
> Hi Ken,
>
> If I recall, your system had a much longer ring-up time than most 
> DRSSTC's and SGTC's. That may account for the different behavior you 
> observed. This effect is normally quite easy to observe with coils 
> that have quicker ring-up.
>
> For example, see the following clip that was captured last year by Tom 
> Warner using high speed video equipment that he usually uses to study 
> lightning. In this clip, the camera was operating at 7200 
> frames/second. It shows one of Greg Leyh's coils operating at about 
> 200 BPS, and clearly shows incremental leader growth from bang to bang 
> as well as the dense glow of countless streamers reaching for the 
> grounded ceiling support beam as the leaders draw closer. The 
> "afterglow" after each current peak is also quite evident. See:
>
> http://www.youtube.com/user/ztresearch#p/u/10/HD46YWM73n0
>
> Bert
>
> Ken or Doris Herrick wrote:
>> Bert (& all)-
>>
>> Glad to hear that my hunch is correct.  Regarding band-to-bang 
>> spark-growth, I recall this from when my coil was working:  I could 
>> produce sparks at rep-rates from 1 at a time to upwards of 20-30/s or 
>> so, and burst-widths from about 8 cycles (I controlled it with a 
>> cycle-counting IC) up to 5 ms-worth or thereabouts, at ~120 KHz and 
>> from a 6"x24" Landergren toroid.  I didn't closely look for it, but I 
>> don't recall seeing much difference in the overall spark length, for 
>> any of those settings.
>>
>> KCH
>>
>> Bert Hickman wrote:
>>> <div class="moz-text-flowed" style="font-family: -moz-fixed">Dex and 
>>> Ken,
>>>
>>> The physics of spark propagation is markedly different for positive 
>>> versus negative sparks (in a divergent E-field, such as around a TC 
>>> topload). All other things being the same, positive sparks propagate 
>>> more "efficiently" in air. Once initial breakout occurs, a 
>>> positive-going high voltage pulse will travel further than a similar 
>>> negative-going pulse. In a diverging E-field, a positive spark will 
>>> bridge a gap at a lower voltage than a negative spark. This is still 
>>> true, even though negative corona will "break out" at a lower 
>>> voltage than positive corona. These "polarity effects" are well 
>>> known by professional high voltage workers and engineers.
>>>
>>> Ken is indeed correct - there is an "optimal" voltage risetime that 
>>> leads to maximum propagation "efficiency". One noted researcher, 
>>> Yuri P. Raizer, has developed a relationship for the optimal voltage 
>>> risetime for a positive spark to travel a distance of L meters ("Gas 
>>> Discharge Physics", page 362):
>>>
>>> T(optimal risetime) = 50*L (in microseconds)
>>>
>>> Unfortunately, although the above relationship appears to work quite 
>>> well for monopolar impulses from Marx Generators, it's not at all 
>>> clear how (or even if) the above relationship can be adopted to the 
>>> complex waveforms of Tesla Coils. Using either the RF waveform or 
>>> envelope leads to relatively low operating frequencies for typical 
>>> coupling coefficients.
>>>
>>> We also know that the longest TC sparks are not obtained during single
>>> single events (bangs), but instead via bang-to-bang growth. Newer 
>>> sparks build on the heated channels of their predecessors when the 
>>> break rate is sufficiently high (>70-80 BPS). This suggests that we 
>>> might try combining polarity effect and bang-to-bang growth by 
>>> polarizing the system so that the highest voltage peak after ring-up 
>>> is always of positive polarity. The positive peaks will provide the 
>>> longest "reach" during propagation. This should be simple to 
>>> implement through suitable coupling coefficient and phasing for 
>>> SSTC, DRSSTC, or DC-resonant SGTC systems, and should cause optimal 
>>> spark propagation for a given input power, frequency, and break rate.
>>>
>>> BTW, an excellent book (also by Raizer), "Spark Discharge", 1991, 
>>> CRC Press, ISBN 0849328683 can currently be obtained for around $38 
>>> or so on Amazon and other large book sellers. This book was 
>>> originally in the $130 range. It is technical, but quite readable 
>>> considering the complexity of the subject. Any serious spark 
>>> researcher should have this title in their library.
>>>
>>> Bert
>>
>>
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>
>
>
> </div>
>