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Re: More on spark delay
Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Kchdlh-at-aol-dot-com>
Peter (& all)-
> Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> certainly some of the more interesting observations to surface recently
> first lets see if we have the time-base correct:
> 140KHz -> 7.1us AC cycle time. 100us = 14 cycles. 5ms = 704 cycles.
> your wording below leaves me totally confused, can you fill in a simple
> time line with voltages:
> cycle voltage
> ----- -------
> 0 100%
> 1 70% (aka a "30% drop")
> 14 ??? stable value ???
Right-- I'll try to be clearer this time:
1. Rise to breakout voltage (Vp-p), ~230 microseconds =~ 32 cycles of
exact-secondary-Fr excitation. Breakout is from a polished 6" x 24" Landergren
2. Toroid-voltage drop from -Vpk to ~-0.7Vpk in 1 cycle, i.e., from 1 negative
1/2-cycle to the next. Sometimes accompanied by a rise of the next +Vpk to
~+1.14Vpk (And I don't seem to see that for every spark. Also, it might be the
preceding +1/2 cycle rather than the following one: can't be sure.). Voltage
measured via a nearby scope probe--and I suppose it may not strictly be "toroid
voltage" but rather, may have a "coil voltage" component.
3. Decline from Vp-p to ~0.17Vp-p over ~100 us =~ 14 cycles.
4. Continuation at ~0.17Vp-p for the ~5 milliseconds duration of the
Repeating my hypothesis: 1. Given sufficient dV/dt, the toroid voltage will
increase, above what it would be otherwise, during (at least, the first part
of) the ~100 us time period, thus producing a longer spark. And 2. The ~100
us time period is caused by the necessity to heat the air and push it out of
the way (so to speak).
It may be mostly the heating, because of this: In the past, I had contrived to
incorporate a mode of operation in which I gated my ~5 ms pulse-burst on &
off. Sixty-four cycles on, 64 off, etc. That was just for the hell of it and
I have quit that, at least temporarily, because I had a rash of MOSFET failures
that I--probably mistakenly--attributed to that mode of operation. But I
noticed that the ~0.17Vp-p level did not change from one 64-cycle "on" event to
the next one. And further, I could clearly hear the "musical note" that was
created by that on & off characteristic during the ~5 ms follow-on time
period. That would imply that the air, "pushed out of the way" during each
64-cycle "on" period, rushed back again--at least, in part--during each
subsequent "off" period. But it stayed hot, with the interrupted spark
continuing to go along the same path for the full ~5 ms period (as I observed),
because the ~0.17Vp-p level r! emained essentially constant.
More food for thought, I hope...