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Re: [TCML] Solid state efficiency, was: mini Tesla coil specs
Ken,
I would think it's the smooth spun toroid you're using which is causing the sparks to
move around on the toroid. This also depends on how many streamers are produced.
If only one streamer is produced, it will move around on a smooth toroid. But if
multiple streamers are produced, they won't move as much because they'll tend to
position themselves evenly around the toroid. When using a corregated rough-
surfaced toroid, the sparks will tend to stick to a bump on the toroid and remain
fixed in position.
Perhaps rep-rate affects it some, I don't know.
Regards,
John
-----Original Message-----
From: Ken or Doris Herrick <kchdlh@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Sun, Nov 15, 2009 2:44 pm
Subject: Re: Re: [TCML] Solid state efficiency, was: mini Tesla coil specs
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>
>
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