A vacuum cleaner motor can be made to run at synchronous speed with
the addition of a diode; actually 2 in parallel for mechanical balance
There is a deal of difference between running at 3,000 rpm
and running synchronously.
Mains vacuum cleaner motors are usually series wound AC brush motors.
The one I removed from a 1100 watt Miele cleaner ran at 18,000 rpm and
drew 5 amps at 240 volts.
Having dismantled it, I soldered two 3 amp 1000 volt diodes across 2
opposite commutator segments (180 deg apart), tucked down behind the
commutator.
A circuit drawing would help. Slowing a motor form 18,000 to
3,000 is by half wave rectifying is a deal different than
synchronous operation.
One would have done but to maintain physical balance, I used a pair
opposite each other and applied a liberal amount of epoxy resin to
stop them flapping about.
The motor is still series connected as before and runs at 3000 rpm (at
50 Hz) quite happily from 30 volts AC where it draws 0.8 amp to 80 volts
AC where it draws 5 amps at no load.
One thing that I haven't looked at yet is the phase change of the
rotor as the load varies but it is probably no worse than an
induction motor with flats machined on it.
An induction motor is quasi synchronous in any case, with
a better lock with the flats. A series commutator motor
is inherently controlled by voltage/current.
best
dwp
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