Re: John Freau's SRSG Dwell Controller

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

Original poster: "James T by way of Terry Fritz <twftesla-at-uswest-dot-net>" <jamest2000-at-att-dot-net>

 Good things come to those who experiment. I tested the Freau Phase Shift
circuit. When all the component values are worked out, this will be the way
to go.
Its elegantly simple.
  My SRSG is 1800rpm, 120 BPS.  My motor is a Leeson, 1/2 horse, 1625 rpm
modified
the be sycnronus. It always had to start it at 140 volts to lock, then
reduced to
120 volts.
   I used an oscilloscope the measure the phase shift in msecs.  This was
done by
putting 4 steel bolts in the extra holes in the disk.  I attached those little
Noebdimumum...   magnets from Radio shack, using a little tape to hold
them. Then
made a little coil using a bunch of turns of fine magnet wire arount some
iron wire.

This produced an excellent trace on the scope

Here are some results. Sweeping Variac from Min to max intil the motor
looses sync.
CAP            CURRENT AMPS        PHASE SHIFT MSEC
20 uf                 0 - 4                   no lock
40 uf                 0 - 4                   no lock
60 uf                 3.2 -  3.5            2.5 - 5.5
80 uf                3.8 - 3.5              2.5 - 4.5
120 uf               5+                       no shift

 About halfway through the motor sound was a bit rougher sounding. I
suppose that is

the resonance problem. Actually this is not a problem because you don't
really need
near as much shift as were getting. I wonder if we could use a little less
phase
shift, to avoid any possible resonance issues, and run at lower current to
boot.
Perhaps use a variac with multiple taps. I'll try it.
 I had expected the motor to lock at its original position and then shift
"advance"
or "retard" from there. Apparently is is shifting from near the beginning
of the
half cycle to so close to the next zero crossing that the motor looses sync.
  Normaly this motor absolutley would not start in sync under 140 volts,
and now it
does. The volt meter was sitting right there but I didn't hook it up. Oops.
  I have the resistors to test Terry's mods. Let you know in a couple days.
Thanks
for the great work guys! This adjustment has always been a real pain,
untill now.
James