[TCML] Spark gap Resistance

[Chris Swinson]

John,


> Chris,
>
> It's been awhile since I worked on this issue.  If you increase  your 
> primary
> inductance
> such that the current is cut in half, the frequency will decrease, but 
> only
> by the
> square root relationship that exists between inductance and  frequency. 
> So
> the
> gap will be firing longer, but not twice as long.  It will only fire 
> about
> 1.41 times
> longer.  So overall, the gap losses will be lower.  I mis-spoke  before, 
> the
> primary
> resistance is not too critical because the gap losses tend to be much 
> higher
> than the primary wiring losses.

A good point, I will ponder over that a little latter.....




>
> By the way, how much longer do you expect your sparks to be using  your
> method of high currents and a high break rate with high frequency 
> operation?
>

I do not expect a great increase. Though if we rule out the spark gap for 
the moment and quench times... then I would expect a 3KA primary pulse to 
work a lot better than a 100A primary pulse.

Resistance is the real killer of high currents, so few primary turns have to 
be used, which starts to lock you onto higher frequency's. I would expect 
that higher current will charge the capacitance of the secondary up a lot 
faster which has to be a good thing ?

Over all, *if* you could build such a system, I would expect you would need 
a general x4 power input to gain twice the spark length. Though this is only 
guess work. I remember someone quoting that for general Tesla coil usage 
though for SG coils of normal design I expected x4 KW input for double the 
spark output, also the reason why I was wondering if larger coils are more 
efficient....

I would expect if you progressed from 100amp primary current to 1,000amp 
that you should gain some good increased spark output. Though with so many 
factors it is hard to say. In theory x2 current input should be x2 voltage 
output.. or should that be x4 power input for x2 spark output... in anycase 
other than building it there is no real way to know for sure....

FWIW, I am actually building a high Q system at the moment, All solid state. 
If Terrys SISG can output 20" spark on 120watts then in theory I should at 
least equal that... The problem for me is that I am using solid state stuff 
at low voltages and higher current, so it is making the design next to 
impossible. I do not really need to say about 1KA pulse over a few fractions 
of a ohm....

As a plan B: also set into motion (though very slow motion I might add) I am 
planning a high Q spark gap design also.. Its once reason I am trying to 
work out all the factors in the design and correct as much as possible. It 
is a leap of faith in the design, its a side step from general accepted 
operation, though if it works or not, I think it will at least give some 
very good data.

My first run of my high Q system was a very weeks ago, I built it wrong and 
missed some bits off, it was out of tune but with 10VDC input it got to 2mhz 
and just enough voltage to draw a arc (maybe 0.5mm) . Not very impressive, 
though considering it was out of tune, in effect driving a 2mhz coil on 
100hz, then it will be interesting to see how it works when it is actually 
in tune...Also IGBT I think I killed, cycles were not going negative the 
inbuilt diode was blocking them, so all in all 0.5mm is pretty impressive so 
far :P

Chris









> John
>
>
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