We have a 5 hp repulsion-induction motor, on our Ashorne Compton organ,
driving a Discus blower by Watkins and Watson circa 1933. The motor is
dual-voltage, single-phase, 1450 rpm [on 50 Hz mains]. It's very
reliable, but on one occasion the switch-over gear jammed and it was
held in induction mode. Consequently, when it was switched on the
following day, it just sat there and overheated the starter box.
I stripped it down to discover that years of switching from start to
run had worn the lobes on the two of the four brush retainers and
locked the brushes away from the commutator. All other parts seemed
to be okay; even the copper segment type bracelet was perfect.
Given that the motor was 80 years old, the chances of finding spares in
this country were remote. So I did the only thing I could: I made new
parts for old. In fact, it was difficult to tell the originals from
the new. I gave the motor a good de-grease and fresh oil in the sumps
and set it to work again.
I'm no expert but it would seem that the repulsion stage lasts long
enough to get the speed up to almost running speed, then the induction
mode is switched in to carry on up to speed. If the induction mode
cuts in too soon the motor will struggle up to running speed. No doubt
someone more knowledgeable than me will have a table of theories for