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phase shifter in use
Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-aol-dot-com>
Previously, all my tests of the sync gap phase shifter circuit were
bench tests, not actually in a operating coil. Now I finally installed
the circuit into my research coil and tested it. I'm still using my old,
crude 1/10HP sync gap which works very well nevertheless.
I first panel-mounted the phase control variac into my TC controller
cabinet along with the phase shift capacitor. I had to rotate the
gap rotor relative to the motor shaft to give me a suitable range
for the phase shifter circuit. I just used one 50uF cap to keep
things simple, instead of the optimal 67uF for this motor. This
is fine; I simply have to remember not to rotate the variac past
90 on the dial, so I don't lose sync-lock. This is not a problem,
because I totally lose all spark output well before I reach 90 on
the dial. This shows that the 90 degree phase control range is
more than adequate. The fact that 90 on the dial equals about
90 degrees of phase shift is just a happy coincidence !
In operating the coil with the phase shifter, it all worked very well.
I was able to smoothly and easily vary the phase, and the sparks
went from short to long to short again as I turned the phase variac
across a range. The best output was within a band of about 10
dial markings on the variac; from variac 20 to 30. It was hard to
really see much difference within in this range, but the sound
could be heard to be louder at variac 25 or so, which may
correspond to the longest sparks. I still have to install a strike
target to more easily determine when the sparks are at their
longest. I tried various ballast settings, and it is clear that my
original setting is best. The best sparks occur just about as
the wattmeter comes to a peak. The best sparks occur when
the ammeter is at an intermediate point. This shows how the
proper sync phase setting optimizes the power factor of the
Tesla coil. All this behavior is visible at a glance when using
the phase shifter circuit.
I'm just generating about 37" sparks at the moment. Even my
small steel 1/8" dia. spinning and fixed electrodes run cool at
this power level.
The phase shifter is especially helpful both for newly built coils,
to find the best phase position quickly, and for research coils in
which capacitors and other components maybe changed, and
for coils which will be run at both 120 or 240 breakrates, which
demand a change in sync phase when the breakrate is changed.
Overall, this electrical phase shifter technique is much easier to
implement than any type of remote mechanical phase shifter.
Such remote mechanical phase shifters would involve the use of
small motors to rotate the sync-motor in it's cradle, or to move
an arm, etc.
Overall, I am very pleased with the operation of the phase shifter
circuit in my coil. I recommend it highly. If you build the circuit,
be sure to use the safety fuse, and to measure the motor voltage
across the variac's range to verify that the capacitor is not too
large in value which would cause too much reso-rise. The
capacitor value is quite critical for best results. Larger sync
motors need larger value capacitors. Use PFC or run type
capacitors, not electrolytic start capacitors which can explode.
Thanks to all those who have given suggestions, improvements,
and reports for the phase shifter circuit. I'm interested in hearing
of all results and findings by others.
Next I'll install my new sync gap, and see how it performs. I don't
really expect to see any difference in spark length, since rotary
gaps are generally not very critical, especially at low powers.
Happy New Year !!