John's sync-adjust circuit

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <ajones18-at-bellsouth-dot-net>

I finally got around to trying out John's circuit. My motor is 1/8 hp
modified for 1800 rpm with 4 flying electrodes and two stationary
ones. The usual setup in other words. I had a few 1uF caps, actually
.93uF, that were wired in parallel for some project in the distant
past and thought I would try it out with these. With 30 caps (27.9uF)
the voltage went to 170v and the motor wouldn't change phase. So I
clipped out five and tried again. No change. Removed another five and
the voltage dropped to 159v, but sync stayed the same. Another five
were removed for a total of 13.95uF. Voltage is now 152v and very
little sync change, but it would change. With 10 caps (9.3uF) the
voltage was 135v and it was starting to look better. With 9 caps
(8.37uF) I was getting about 20degrees of adjustment. At 7.44uF there
was a slight increase in adjustment but not much. Voltage was131v.
With 7 caps (6.51uF) the voltage dropped to 128v but no increase in
adjustment. With 6 caps (5.58uF) the voltage dropped to 122v but extra
rotor movement was hard to determine. With 5 caps (4.65uF) the voltage
dropped to 121v and I was getting around 30degree of adjustment.
Cutting out one last cap which left 4 (3.72uF) the voltage went to
119v but it increased instead of decreasing when turning the variac
the same direction. So I figure on soldering the last cap back in and
using 5 (4.65uF). I was using Terry's modified strobe light to watch
the sync change during all this.

I was hoping for the 90degrees that some have reported, but for some
reason I never could get more than about 30degrees. I still have the
handle on the motor for rough adjustments when changing transformers
and tank capacitors. The sync setting is very different when using
3000VA with .09uF and using 360VA with .007uF. 

I knew when I started that there was too much capacitance, but I
figured it was easier to clip out some than to have to solder them
back in. And the run times were just a couple seconds or so, shouldn't
have hurt the motor. 

Maybe this can be of use to someone else. I imagine each motor would
need different capacitances since no two people are going to grind the
flats the same and use the exact same motor. These factors will
probably make each have a slightly different current draw and require
a different value cap. But these numbers should get a motor and cap
close enough without all that experimenting I did.


Alan
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