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Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
The thick nature of the QCW spark would be like resistors in parallel, pulling more energy, like Steve says. I also imagine it would have a great impact on the capacitance value of the spark. I think the QCW shows that current can have more of an impact on spark length than voltage, owing to the "ampy" nature of CW systems. I would also think it would greatly impact the capacitance.
Steve, do you have any numbers on how much do the streamers detune your coil?
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Theory and formulae are not my strong point, but i do have some experience...
All i can really tell you is that there are three million variables to consider. Of course, C resistance, and L resistance play a role, but the resistance and inductance of the bridge and IGBTs play a role, resistance and inductance in the buss caps play a role, and even things that are rarely considered play a role, even if only a tiny bit.
If you have lower quality buss caps with high resistance, it will take many more cycles for the primary current to ring up to a given current than a lower resistance capacitor.
That said, calculating it with some formula is highly impractical, when you could just hook it up and test it out.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
It's perfectly possible to do the initial design ignoring losses. I have shown that the optimum design of a drsstc is as described here: The energy transfer time for "mode" a:b:c is b/4 cycles of the driving frequency.
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Thank everyone so far for the help.
I do know that the sparks are none linear because the resistance and capacitance (as stated above) get lower and higher respectively depending on the length and overall volume of the spark.
I find this problem very intriguing, maybe it's just me but I find that every thing in life can be explained with mathematics. It may take some time though to find the correct math for this problem.
I may need to get a super high voltage R and C meter and test over one foot of different kinds of spark kidding...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Antonio, your method is the same as what Steve Ward discovered empirically, it's the way that he tunes his larger coils now. But, you sidestepped the issue of streamer loading: your model doesn't predict what the voltages and currents will be if breakout occurs a substantial time before the burst is finished, which in a high-performance DRSSTC it always does. So, it can't predict what length of spark the coil will generate.
wrote ... Note that for these circuits there is always the possibility of driving at one of the resonances, what produces a continuously growing output, that ideally can result in any voltage gain. But the input current grows too at the same rate. For given input and output capacitances, and output inductance, The design procedures (a) and (b) above always reach a given output voltage faster, and with smaller maximum input current.
This in a nutshell is the difference between Ward's tuning method and mine. I just drive it at one of the resonances, because my PLL drivers can't produce two frequencies at once. I believe that my method works better with small, high-frequency coils, and Ward's works better with big ones.
With a small coil, the burst contains so many cycles that one or other of the two resonant frequencies will always become dominant, and the other one die away. A PLL driver only drives one of them, and a feedback driver will settle to one or other because the loop gains for the two modes can never be exactly equal.
But in a big coil the burst could only be 5 or 7 cycles. Both resonant frequencies are significant, and the Antonio/Ward method works both of them together to maximize energy transfer.
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Calculating primary ring-up time in DRSSTC
kidding...
