Re: Microsim Modeling - SRSG

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Jeremy,

At 12:17 AM 4/28/2003 -0700, you wrote:
>Hi,
>
>I've been experimenting around in microsim trying
>to figure out the optimal settings for a rotary
>spark gap.
>
>The problem which is usually not evident is that
>unlike the real world, microsim ass-u-me-s unlimited
>power. It doesn't know or care that a transformer is
>designed for 60mA, it will draw whatever it takes from
>the secondary to charge the tank capacitor. Throwing a
>current probe on the other side of the transformer
>will show in excess of 40A on the primary. That loud
>snap was the tiny 15A breaker signalling it's
>displeasure with the situation. That smell is the 14
>gauge wire in the wall beginning to smolder.

You need to model the 15/60NST.  See:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/BigCoil/BigCoilSCH.gif

By adding winding resistance and reducing the coupling, the short circuit 
current will be reduced to 60mA just like the real NST.

>So, do we fire on 60Hz peaks, giving 120BPS, or
>should we try for more BPS in hopes to achieve
>more spark length performance.

If you reduce the cap size (resonant or less) you can get higher BPS.  Not 
sure that does any good at all.


>Well, to answer that question we have to drop
>the assumption that unlimited power is available.
>One needs to figure out how much current the
>transformer can draw. Using ohms law we slap a couple
>of resistors in the microsim circuit on the secondary
>to make sure that no more current is drawn than
>realisticly possible. For a 15/60mA NST, ohm's law
>tells us that's 250K, so I put 125K resistor on
>each side of the secondary's windings.
>
>Now the story changes.
>
>No longer is it acceptable to fire on 60Hz peaks:
>because there is limited current available, the
>capacitor may not yet be fully charged -- the voltage
>across the capacitor is not necessarily in sync with
>that of the line feeding it.
>
>Generally, the faster the capacitor charges, the
>better. The 60Hz AC half cycle is 8 1/3 ms long, which
>means the capacitor has exactly that amount of time
>to charge and discharge. At exactly 8 1/3ms there is
>no voltage coming from the secondary, so the capacitor
>dumps whatever it's got up until there into the core
>of the secondary. This is stressful for the
>transformer if it is done for many cycles because
>it forces many amps into the secondary as the
>capacitor discharges.
>
>This is why LTR (Larger than resonant) capacitors
>fire AFTER the peak, but before the 8 1/3 ms
>deadline, and why it may not be advantageous to
>have more than 120BPS with an LTR cap.
>
>Resonant caps usually charge to their supply's
>peak voltage at 13.4ms. At 8 1/3 ms the charge
>on the capacitor is not quite enough to trigger
>the spark gap, instead it dumps it's charge
>into the secondary transformer windings. The
>transformer converts it to an electromagnetic field
>within the core which combines with that already
>created by the primary windings. Then the field
>collapses as the polarity reverses on the primary.
>
>There is an extra boost to it now because
>instead of just electromagnetic energy from
>the primary, there is also energy added from
>the partially charged capacitor in the core.
>(From the last halfcycle.)
>
>When all that collapses back into a reversed
>current, it takes just 5.1ms to achieve full
>potential on the capacitor now. This cycle
>repeats until the capacitor voltage reaches
>several magnitudes greater than that of it's
>supply. (Resonant rise.) Sync gaps with resonant
>capacitors usually don't improve performance,
>instead a properly quenched static gap is best
>if one wants to take advantage of resonant rise.
>
>I've found in the LTR case that the best "time"
>for gap conduction is this: Calculate gap conduction
>time from the RPM and diameter of the rotating
>electrodes. (disc diameter and also electrode
>cross section diameter) Subtract that from 8 1/3
>ms to find the best time to fire. Using trig, sin()
>calculate the phase angle and adust the gap
>accordingly. This ensures that the capacitor will
>have the full halfcycle to charge minus the time
>needed to oscillate the tank.

See:

http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm

http://hot-streamer-dot-com/TeslaCoils/MyPapers/modact/modact.html

http://www.richieburnett.co.uk/indkick.html#kick

Cheers,

         Terry