5HP rotory elect. phase control

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kreld-at-juno-dot-com>

John, all

  There has been much talk about electronic phase control for rotory gaps
lately, so this encouraged me to finish my 5HP 3600 RPM rotory project. 
I was a little worried about being able to make John Freau's phase
control work on such a large motor, but it does work after all.  The
optimal capacitance is around 85 uF using a 10 amp 120 volt variac for
control.  Some may be asking why such a large motor for a 12" disk.  My
other 2 HP sync. motor was OK untill I added larger electrodes, then the
motor would not lock in sync.  The new motor is a Dayton brand from
Graingers.

 First problem, the motor with disk & electrodes installed pulls 60 amps
-at-240 volts in start mode, but only 5 amps in run.  This start torque
sheared all the hub bolts at one time during testing, so a soft start
system was made to control the motor current.  This brings the start
current to 40 amps and slows the initial speed up.

  Several delay circuits add a 3.5 ohm 3000 watt resistor inline with the
motor for the first 2 seconds while also bypassing the variac which would
smoke under these conditions.  Then a contactor shorts the resistor and
the motor comes up to full speed.  Two seconds later the variac bypass
contactor opens and electronic phase control begins.   There is roughly
60 deg. mechanical dwell of adjustment possible.  Adding more
capacitance, up to 200 uF, helped in no way.  Less than 80 uFand loss on
sync. would occur in at full variac inductance.

  The new electrodes are 3/4" x 5" with aluminum plates on each side of
the G-10 disk for added streangth & heat sink ability.  This rotory will
be used on the Biggg Coil this season for better power handling.

Pic's of the rotary & system are at  www.flash-dot-net/~kreld/misc.htm

Coiling in Oklahoma

Kevin E.

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