Re: DRSSTC design procedure - draft

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Antonio Carlos M. de Queiroz" <acmdq-at-uol-dot-com.br> 

Tesla list wrote:
 >
 > Original poster: "Steve Conner" <steve.conner-at-optosci-dot-com>

 > I believe that the energy in the secondary self-capacitance _does_
 > contribute, and what's more, any energy in the primary tank at the time of
 > breakout contributes too. I actually think this is the secret of the
 > DRSSTC's efficiency. In Steve Ward's successful self-resonant designs, the
 > primary tank is full of energy at breakout. Jimmy H. originally tuned his in
 > a similar way to what you suggest, to get energy "transfer" in the classical
 > sense, but he found the spark output improved a lot when he retuned it to
 > drive at one of the resonances.

The energy in the primary can only contribute to the output if the
driver continues to run after breakout, and through many cycles because
of the high Q of the system. I am considering a system adjusted so
the driver stops when the primary is empty, much as in a conventional
Tesla coil.

 >  >Mode 31:33:35 results in k=0.12 and energy transfer in 8.25 cycles.
 >  >(The formula for k is a bit complicated to list here, but is
 >  >implemented in my sstcd program.)
 >
 > This is very interesting. The system I've been playing with had k=0.11, but
 > C1=12.5nF and L1=42uH. I tried exciting it at various frequencies but the
 > lower resonance seemed to give the best results. When tuned in this way it
 > took about 30 cycles to produce a decent spark. The peak primary current was
 > about 400A, the bang energy something like 5-6 joules and the spark output
 > was 36".
 >
 > It hit 36" regularly and would have probably gone even further, if it hadn't
 > exploded on the first run.

Because you are driving the system at one of the resonances. The input
current then grows along with the output voltage. Surely works, but is
hard for the driver.

 >  >there is always a design as the one above that
 >  >requires less input current to transfer the same energy in the same
 >  >number of cycles (or I think so...).
 >
 > According to your method then, I should be able to get the same spark output
 > with 200A peak current in 8.25 cycles? I need to check this out. My coiling
 > stuff is all dismantled at the moment, but I can run a PSpice simulaion of
 > the two coils side by side.

The simulations show this. But note the large primary capacitor that was
required. With 12.5 nF the mode would have to be higher, and the
resulting
k maybe too low for practical implementation.
It's possible to design the system so any voltage is reached in any
number
of cycles, but the element values can become impractical if a too low or
too high mode is used (too low impedances, too low frequency, or too low
k).
The restrictions on k are about the same for a conventional Tesla coil.
Something between 0.1 and 0.2 easily result in viable designs. Low k
produces larger voltage gain, but precise tuning may be difficult. High
k decreases the voltage gain, but this can be compensated with a larger
input capacitance. If the current grows excessively, larger inductances
bring it down. (The input current is inversely proportional to the
square root of the inductances, for fixed capacitances. The driving
frequency too.)

 > If the improvement that this design method gives is as drastic as you
 > suggest, then we could find a way of living with the hard switching that is
 > an inevitable consequence if you don't drive the system at one of the
 > resonances.

Driving at the central frequency results in practically perfect soft
switching. The same at the resonances.

Antonio Carlos M. de Queiroz