salient-pole motor

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Rob Maas <robm@xxxxxxxxx>

Hello All,

I made an attempt to convert an asynchronous motor (2950 rpm, 50 Hz!)
to synchronous operation.

The diameter of the rotor is 45.4 mm, and the rotor has 16
poles. I grinded two flats of 15.5 mm (d_f/D = 15.5/45.4
~ 0.34), 180 deg. apart. After re-assembly, the motor now runs
indeed at 3000 rpm, as checked with a strobe, converted along
the lines described by Terry Fritz in his Radio Shack strobe
conversion paper.

Is there a criterion for the 'correct' ratio d_f/D ? (I saw some
people made them as large as d_f/D ~ 0.5).
I noticed that in certain rotor-orientations the motor has difficulty
to self-start. A small tug immediately makes it start: does this
signify the flat is already too wide, or should it made wider?
I should add that I did not really observe the 'starter windings',
but they are probably somewhat hidden beneath the run windings, because
out of the stator come four wires; two are connected to a 2.5 uF
capacitor. Is there a reason to change this value in this new mode
of operation?
It is a rather small motor: the power rating is 150 W (~ 0.2 hp).


thanks in advance,  Rob