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More: 120 bps vs. 240 bps comparison tests
<< cap spark
watts watt amp length power charge
> BPS Joules calc meter meter inches factor % eff. %
> 120 3.85 463 550 2.6 42 88 84
> 240 5.41 650 800 3.8 42 88 81
>>
Malcolm, Barry, all,
I should mention that in the table above from my previous posting,
that the 240 bps joule figure is based on two bangs, so the figure
is really joules per ac half cycle.
But I did some more tests:
First, I adjusted the gap phase by a few degrees to better equalize the
bang sizes, this had no noticeable effect on the TC operation or
efficiency.
I started thinking some more about the whole comparison, and I
started to wonder if I might be seeing the effect of a sort of "sweet
spot" in the coil, which could be skewing the results. As a cross-
check, I did a new test, running the coil at 240 bps with the same
bang sizes as previously used at 120 bps. This of course doubled
the input power, and the spark increased by 23%. Next I ran the
coil at 120 bps, but used the smaller bang size equal to that used
previously at 240 bps, and of course the spark was shorter. Here's
a new table showing the new results:
cap
watts watt amp spark length
BPS Joules calc meter meter length increase
120 2.7 325 400 1.8 34"
240 5.41 650 800 3.8 42 23%
120 3.85 463 550 2.6 42
240 7.7 926 1100 51 21%
These results suggest that doubling the power input by a doubling
of the break rate (keeping bang size the same), gives about 1/2 the
spark length benefit as a doubling in cap size instead. A doubling
of the cap size (bang size) gives about a 41% spark length increase
(shown by other experiments). So these new tests continue to
indicate that longest sparks for a given wallplug input power can be
achieved with low break rates with larger caps. Again the 240 bps
joule figures in the table above are for 2 bangs (1/2 ac cycle).
These tests also show that charging efficiency remains good at the
higher break break rate. The inefficiency of high break rates must
be occuring due to the physics of spark growth in the air. The
sparks are brighter and fuller though at the high break rate, so it
would seem that at high break rates, the power is going partially into
creating fuller, brighter sparks, and partially into making them longer.
Yet, Greg Leyh's sparks seemed to grow tremendously as he raised
his break rate in his excellent DC powered TC (he has equal bang
size at all break rates). I forget the exact figures though, i.e. for a
doubling of the break rate, how much longer did the sparks grow?
John Freau