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New, corrected, Sweet (and sour) spot tests, etc.
Malcolm, John C, Bart, Richie, all,
**** All my recent tests were in error. There was a short in the
secondary coil that was affecting the results (I think). I first
tried installing a 3" by 10" toroid and running the coil at 280
watts to see if the spark increased (which would mean that
the 4" by 13" toroid was too large). It seems that the spark
did increase a little, but I noticed arcing on the secondary.
I knew the secondary had burned spots, but I didn't think it
was affecting the results. But I think it may have. Today it
was very humid, and this may have been increasing the spark
lengths too, I don't know. Anyhow, I removed the burned turns
and repaired the secondary and redid some tests (below), and
got results more in line with what I originally expected. I'm
sorry about the confusion.******
New tests:
In these tests, I ran the TC at various power levels, and with four
different toroid sizes, to see how far the spark length would vary
from the square law predicted lengths. Spark length shortfalls from
predicted lengths might mean that the coil is becoming inefficient in
some cases.
All tests at 120 bps. 42" is a reference max spark length. (This
table can be more easily analyzed if it's printed out on paper, so
the headings don't scroll out of view as you scroll down.)
pri predicted
Watts cap W Top" tap length length actual shortfall%
280 210 3x10 18 29" 27" 7
280 210 4x13 19 29 27 7
(note above: the smooth toroid size no longer mattered)
400 318 4x13 20 35 35 0
530 440 4x13 21 42 42 0
620 498 4x13 21 44.5 45 0
(note: now TC efficiency is constant from 35" to 45" spark and
with same toroid)
280 210 4x17 20 29 24 13
400 318 4x17 20 36 34
5.5
530 440 4x17 21 42 40 5
(note above how the 4x17" toroid is now inefficient, it may be
emitting corona from its corregated surface. The smooth spun
4x13" toroid seems better despite being smaller.)
Here's a re-test of the test of Malcolm's suggestion of using a large
toroid to hold the voltage constant when increasing the power to see
if the spark gets longer:
280 210 3x10" 18 29 27 7
560 440 6x26" 26 42 38 10
These results show that by doubling the power input, and using
a rather large toroid to attempt to keep the output voltage constant,
the sparks still increased by 41%, even more than in the original
test. This suggests that streamer current is very important too
for creating long sparks. The sparks were very hot and strong
using this large toroid, BTW.
Then I tried higher power:
750 6x26 26 48 47
2
(here, the TC can be seen to be remaining on the square law curve,
the 2% shortfall is within measurement error)
Next, I tried the 4x13 toroid at 750 watts:
750 48 (spark did not reach 48")
(I will do more tests of this)
In any case, the results above show that:
1. Just ramping up the power (or maybe the break rate too) may
give false results; the coil has to retuned for each power level
(nothing new here).
2. The toroid size may be less critical than the last tests suggested,
it's still very important though. Smooth toroids seem much better,
in some cases, and the smooth toroid easily produces just one
streamer when a bump is installed, even when the sparks are
3.4 times the toroid diameter.
3. Sour spots occured now only at very low power levels. The
square law held, from 400 watts to 750 watts. I am pleased
with the results of these new tests which fit my original
expectations, and added new data.
4. Thus, when making comparisons of 120 and 240bps, it may be
acceptable to let the spark length vary, as long as the TC is
known to be "on the curve", from tests such as the above. I
will re-do the 120 vs. 240 bps comparison tests.
Cheers,
John Freau