On Wed, 22 Feb 2006 18:17:17 -0700, Jim Wilson
wrote:



Anyway, Jon's idea was to put a pair of 120V incandescent bulbs in series
with each other and across the pony motor. I did. Lo and behold, my pony
motor is an excellent generator. The lamps light up just as if I had
plugged them into an outlet. :-(

The voltage supplied to the pony motor via the contactor is 240V
according to my voltmeter. When the pony motor is acting as a generator,
it supplies 245VAC. There's no sag in voltage when I hook up the lights,
so the field in the rotor must be pretty substantial.

I still don't understand why the pony motor gets hot, though. With the
motor leads open, there's no load. Since it does no work, why is it
heating? Losses shouldn't be *that* bad.


The run capacitor is supplying magnetising VARs to the pony motor. Try to
arrange to either:-

1) Open circuit the run capacitor, which will stop the motor being excited as
an induction generator.

or

2) Short the pony motor (yes,really). This will cause the voltage to collapse
and prevent the motor/capacitor combination from self-exciting.


If you have a spare pair of contacts that can do this, or fit another relay
fed from one of the existing ones, your problems should disappear.


Mark Rand
RTFM