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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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