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Re: [TCML] Spark gap comparisons



Hi John,

It's not surprising to me they performed about the same. The sync rotary and the trigger gap both are controlled timed events of the mains frequency. So in that respect are similar. The rotary however does have the adjustment of where to fire along the waveform and I suspect the trigger was not adjustable (to fire after peak, maybe before peak). Triggered gaps are also prone to the triac not turning off periodically without adding some extra circuitry to ensure turn off. There are probably some slight differences between the two gaps but the cap voltage was probably very similar.

I think gap comparisons are very difficult to make especially trying to compare different types of gaps, especially comparing a static gap to either a rotary or a triggered gap. They are different beasts and the static gap firing voltage is very dependent on thermal regulation, surface, size, etc. where a rotary is not (even a trigger gap is not as it's firing is independent of the electrode geometry or temperature).

I'm not sure I understand what you mean about rotary gaps not capable of firing at peak due to voltage rise upon electrodes approaching. Can you give more details to your hypothesis?

Take care,
Bart

FutureT@xxxxxxx wrote:
In one experiment, I compared the performance of a 2 gap 120 bps sync  rotary
to a single 120 bps triggered static gap.  In both cases I got a  42" max
spark length using my TT-42 TC.  Using the rotary, the gap light and  sound
emitted was quite low.  Using the triggered gap, the gap light and  sound
emitted was intense.  The gap spacing when the rotary fired was  small.
The gap spacing of the triggered gap was large at 5/8". Unfortunately I don't
remember if I measured the firing voltage in both cases, but input  power
draw was the same.  The triggered gap
may have been capable of firing at a higher voltage for some reason.   I have
speculated in the past that rotaries may not be capable of truly firing  at
a peak voltage because of the way the voltage rises as the electrodes approach. I'm not sure if that's a valid idea. If both systems fired at the
same voltage, then it's interesting that they both gave the same  spark
length despite the very wide triggered gap spacing.  One might say  that
the 2 gaps of the rotary introduced extra losses.  Yet in other  experiments
I compared the performance of 2 gap and 4 gap rotaries, and didn't  see
a difference in spark length output.  Perhaps some slight  quenching
differences occurred such that the negative and positive aspects
canceled.  Various multi-pipe gaps were tried on this coil and the  sparks
were considerably shorter and more feeble looking.  I reported all  these
results in the past. I'm re-posting them for the benefit of new list members. John

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