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Re: [TCML] MAX SPARK FOR FIXED VOLTAGE



Hi Dex,

Unfortunately, there are no simple answers to your question. The quest for maximum spark length has been the coiler's Holy Grail for well over 100 years. However, even the very best available modeling tools, such as Bart's JavaTC or FANTC, model electrical behavior for _non-sparking Tesla Coils_. Although they can model the voltage at which initial breakout should occur, once sparking begins about the best we can currently do (regarding spark length) is to estimate "best case" spark lengths using John Freau's empirically-derived power-spark length relationships for the type of coil and operating mode.

This is not from a lack of trying. It's from a lack of usable dynamic leader/streamer models that can be used with the repetitive complex waveforms of Tesla Coils.

In a nutshell, we don't understand precisely how resonator and topload energy "couples" to attached sparks. Or how topload and resonator parameters relate to spark propagation. Or how spark length is individually or cumulatively affected by frequency, resonator impedance, topload capacitance, topload ROC, peak output voltage, break rate, coupling coefficient, or bang size. Nor do we know how to accurately model the dynamic, nonlinear, distributed, and random branching nature of Tesla Coil leaders and streamers, or the effects of residual space charges, or residual channels left by previous bang(s). It is clear that simple lumped models, SPICE, or other lumped circuit modeling tools alone will not be up to the task.

Frankly, I don't foresee this situation changing any time soon. There is very little scientific interest in Tesla Coils. Those few areas deal with heavily coupled, non-sparking resonant transformers for pulsed power applications or educational demonstrators. Practically speaking, the only folks who actually study Tesla Coil sparks to any degree are a small subset of hobbyist and professional Tesla Coilers. The majority are hobbyists simply trying to achieve maximum spark length for their systems.

Now, back to your question:
I have no doubt that, given the same resonator and break rate, with toploads that are scaled to break out near their planned maximum voltages, then the longest sparks will occur with the 300 kV system, the next longest with the 200 kV system, etc. Further, spark lengths will scale as the square root of input power, and the most efficient systems, (such as DRSSTC's) will provide longer sparks for the same input power. But I can't tell you what the maximum theoretical length might be, nor (besides a lot of design rules of thumb) how best to achieve it.

Bert


Dex Dexter wrote:
Hi,
Thanks for the answer.
I'm not interested in losses as already said.
Neither I'm interested in low repetition rate operation.
I'm interested in a VERY high repetition rates with fixed
primary energy what (roughly) gives fixed output voltage.
If necessary ,4500 pps to be used with 100 khz solid state
system.
To clarify,you basically say that with generated ~100 kV secondary peaks
it's not possible to get more than 5 feet discharge no matter what you do?
What would be aproximate maximum for ~200 kV?

Dex --- resonance@xxxxxxxxxxxx wrote:

From: DC Cox <resonance@xxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Cc:
Subject: Re: [TCML] MAX SPARK FOR FIXED VOLTAGE
Date: Tue, 10 Mar 2009 17:22:17 -0700

Output potential is Vsec = Vpri (peak) x 70% x SQR(Lsec/Lpri).

Also max potential is a function of inductance, whereas:  Vsec = L x dI/dt
(rate change of current with respect to time).

Inductance goes up as the square of the radius of the sec coil, and
generally large inductances produce higher potentials.

Spark length depends of total power and also the repitition rate (pps) of
the spark gap and it's ability to properly quench at the power level
being used.  Once a large volume of ions are created above the HV terminal,
then it's a "pumping action" every time the sec fires into this ion cloud.
The residual ions help to make the spark "grow" in length even though the
potential is lower.

It's quite possible to get 4-5 ft sparks at 100 kV IF the power level and
rep rates are high enough.  As an example a typical coil running 450 pps on
the break wheel, with a 100 nF capacitor (0.1 uF), runs a true 1 million
volts with a 14 ft. long sec spark.

Again, rep rate, power levels, and efficient quenching are required to
produce high performance even at lower potentials.

Solid state coils exceed these performance levels due to their highly
efficient switching and lack of losses used to heat the spark channel in a
standard
type spark gap.

If you operate any Tesla coil in a single shot mode, firing once every 15
seconds, then this spark length is a very accurate indicator of the coil's
maximum output potential.  It agrees with the equations I have listed above.

>
>
Dr. Resonance

On Tue, Mar 10, 2009 at 11:37 AM, Dex Dexter <dexterlabs@xxxxxxxxxxx> wrote:

I have a good question I don't know answer to.
QUESTION:
What is aproximately maximum spark lenght possible for a given output
voltage Tesla system generates?

Regardless of the efficiency,how long spark can be produced by a Tesla-type
impulsive devices with voltage levels:
1) 100 kV
2) 200 kV
3) 300 kV

Can a high power impulse source,like a Tesla transformer,put out a 10 feet
long spark with 'only' 100 kV voltage peaks?
To accomplish that it is free to use any power input level,any size and
shape of  a terminal capacity,any firing rate wanted,andthe best high
frequency excitation waves mix.DRSSTC,VTTC,etc.
The only limiting thing is not to exceed 100 000 V terminal potential.
Supposing a normal atmosphere enviroment is that possible?
I know that in no circumstance 50 kV can close 5' wide gap unless directly
conducting path is formed somehow,or a
strong external ionization occurs ,like exposure to a flame,extremely
powerful lasers,but Tesla transformers are the
champs of 'spark pumping' and I was wondering what could be done with 100
kV.
Thanks for  your answers and explanations.

Dex



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