Re-test of 120bps vs. 240bps comparison
I re-did the 120bps vs. 240bps comparison after fixing the short
in the secondary coil.
BPS Toroid W CapW Div 1.75sqrtPOWER shortfall length
120 4x13" 400 318 4 35" 0% 35"
240 4x13 800 318 4 49 14% 42"
(this shows that the spark increased about 20% using the higher
break rate. But using 120bps, with a larger bang size, and with
less input power the spark is longer, and tends to follow
the square law for a 40% increase:
Another new test:
120 4x13 750 48" 2% 47"
(this shows that at 120bps, the large bang size, at 750 watts
gave a longer spark than the smaller bang size at 240bps, at 800
watts. This new test continues to ~follow the square law for about
a 40% increase in spark length with a doubling of the power input.
240 3x10" 800 318 4 49" 42"?
240 6x26 750 48 19% 39
240 6x26 800 318 4 49 less than42
(this shows that the large toroid is too large for 800 watts at 240
bps, but it's not too large for 800 watts at 140bps.)
These tests re-confirm that a larger bang size at 120bps gives about
double the benefit of a smaller bang size at 240bps, for the same
power input in both cases. Power is being measured at the wallplug
and at the caps to insure that the charging circuit is not causing the
inefficiency of the high break-rates. These tests suggest that
creating longer sparks by using a high break-rate is not an efficient
way to build a Tesla coil. I don't imagine that other coils would
behave differently, but we'll see.
I found that when tuning a TC at 240bps, the primary tap point is about
the same as at 120bps, even though the spark is longer. Although the
sparks get longer, they do not seem to demand that the tap point be
moved outward, as would be required with a larger bang size. The
tap point is corresponding to the bang size, not to the spark length,
interesting. In some cases, the primary tap point needed to be
moved *inward* at the higher break-rate, even though the sparks
were longer. This was unexpected, and I don't have an answer for
this. I did find also that the tune point seemed to be less
precise at the higher break-rate. This strikes me as possibly a
bad sign....a sign pointing towards inefficiency for high break-rates.
These tests suggest that toroid size should be proportioned to the
expected spark length, not to the input power or break-rate. This
is because higher break-rates will produce shorter sparks for a given
input power, and will therefore work best with a smaller toroid.
In the past, I did some tests at 60 bps, and the coil seemed to be
even more efficient than at 120 bps, although these tests should
be redone while observing cap watts. It would be interesting if
60 bps turns out to be even better than 120 bps. There is also the
question of exactly what break rate is best; 90bps, 110bps, etc, or
is there a range in which efficiency remains very similar.