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Re: [TCML] Spark gap Resistance



John,


If the current is less overall, then the gap losses are  lower.

I would have thought that once the spark gap has fired that dumping more current in that single time would be lower?.

Less current must mean more cycles to transfer the energy which must mean a longer spark gap conduction time. A longer time must be more losses... I do not see how less current over the gap will work unless you treat the gap as a 10R resistance or something of that nature. On that basis more current will make the problem worse.. from 100A to 10,000amps there would be no gain on that basis... If a Larger tank cap can pulse more current, then this is just making the problem worse if the spark gap is a resistor.

Using a high
impedance
primary results in less overall current and less overall losses. When more
inductance
(more turns) are used in the primary, the inductance increases more than the resistance increases, thus the primary losses are reduced. The Q is higher.
The result is that
both the gap losses and the primary losses are reduced. Of course this only
works up to a point.

I can understand that, Though I would have thought it better to reduce the inductance and gain a much higher peak current which cycles a lot faster to reduce spark gap losses.

I am looking from the point that we could have 100amps for 100us or 1,000amps for 10us. if the current over the gap gets worse the high the amps, then is there a chart or something to overlay this data ?

I look at it that once the spark gap is conducting ramping the current higher would transfer a lot quicker.... this can only happen if the spark gap has zero resistance across it. even a few fractions of a ohm at high current.

Or on the other hand ramp up the current and the frequency to make the cycles even faster and use higher Q secondary coils..

I will have to take it as the spark gap has to be treated as a resistance to support your statment ?

Make me think of jacobbs ladders, do they not draw more current the longer the spark is drawn out ? I have not looked into that much, but as the arc grows resistance would have to go down in order to pull more current ?


At some point the secondary wire will be  too
thin and will show high losses.


So are you saying use a lot of primary turns with a thick wire secondary ?




Generally low frequencies are believed to be more efficient in  producing
long sparks.

I know this is the case, but other than the frequency vs RSG quench times I would have thought higher frequency's would work better.

I did some testing a few weeks ago with frequency's. I only ran at 12V levels, but I found that x10 the frequency double the "range" of the transmission, and double the frequency x4 the efficiency.

In Tesla coil terms, a 100khz coil coil say 50" high , or 1mhz coil 100" high. this is what I state as the "range". 1mhz seems to double the energy area.

I obtained a x4 voltage increase in efficiency each time the frequency doubled. This would mean a coupling factor of 0.4K at 100khz or 0.1K at 200khz, over all the efficiency would be the same. Though I would take a low coupling factor as better due to less mutual inductance on the primary..

The primary must be be a higher Q as it is effected by the inductance of the secodnary, so a tighter coupling should work better ?

If the primary was 10uH on its own, then with the secondary in place it could be like 200uH ? Trying to think what the current across the gap would actually be on that basis...


Maybe something in the range of 30kHz to 150hHz. Also at higher frequencies, it's harder to achieve a first notch quench. The sparks themselves may grow
better at low frequencies.


I think lower frequencys just take longer to cycle across the spark gap. for example 100khz for 100uS or 200khz for 50uS. If you take that 100khz quenches at the first notch for best output, then progress to 200khz keeping the same spark gap operation, then the cycle time will be twice as fast and the spark gap will quench at the second notch and reduce efficiency. 200khz should be a higher Q factor for the secodnary and give better results. The frequency is not really to blame is the slow spark gap....

On that basis if you could quench at 50uS and use 200khz, the total time across the spark gap will be half and I would assume reduce losses as the conduction time is only half. On that basis you could probably get away with a higher current pulse.

I am looking at the total losses over actual conduction time. Is the spark gap really working better at a lower current , or is it just becasuse the primary Q factor is higher ?

If we set asside spark gap losses for a moment, would a higher current though the primary be better then ? Pass 1,000amps in 1uS rather than 100amps in 1uS kind of thing. I am not sure how Q factor would overlay towards the current aspect of things though..

As you said this only works to a point, at what point does adding more turns not help ? If increaseing primary Q is good then more turns should be better. At some point maybe resistance starts to become too high and burns up power that way. Seems a very fine line between the 2 though.





Large coils are generally more efficient than small ones.

But passing more current over the gap is bad ? I assume here the larger coils would have to use a lower coupling to increase cycles and reduce the current though the gap ?




Tank caps generally are able to provide their current fast enough for
TC operations.
Generally high breakrate coils need more input power to produce a  given
spark length. It's not known exactly what breakrate is best. It may vary
somewhat among coils.   Somewhere between 100bps to 200bps  usually
works well.

I like the simple method of drive at double the line frequency

Chris


P.S. sorry to pick apart your post and waffle off topic somewhat!

So many factors to take into account, it is hard to work out actually where the losses are..... I am sure my 500W coil only outputs 100W worth of energy, it also suggests why the voltage gain formulas are so much out along with my simulations which show a lot higher output voltage than there appears to be...

I was actually thinking primary coil losses are the factor just on resistance alone. for example 50amps over 0.100ohms = 250watts, or 250uH at 100khz for the same 250watts or there abouts.

So maybe pumping 500W into this type of setup is pointless if the primary only pulls 250watts anyway. Also makes me wonder that less primary inductance and resistance is the way to go.... It would pull more amps, so would need a much stiffer tank cap in order to provide the current...... though overall going by what you state about spark gap losses, it would all seem pointless...

P.P.S. Glad I am working towards a solid state spark gap now :P I actually think the power losses are half in the spark gap and half in primary resistance... again why I think speeding up the spark gap conduction time would be better in reducing spark gap losses...

All once big headache really.
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