On Mon, 7 Oct 2019 16:04:45 -0700 (PDT), wrote:

Hi Comrades, please what is the simplest way to reduce the speed of a single phase induction motor to about 50%?
also can a universal motor run for 24 hours on 90% load? (with all name plate ratings observed)
thank you.
It depends on what type of single phase induction motor. The
typical single phase motor that you see powering bench grinders and
the like will often have a centrifugal starting switch, a potential
relay, or an electronic switch that controls the starting winding.
These cannot be made to run at 1/2 speed without extensive
modification and a power supply that provides AC at 1/2 the frequency
the motor is rated for. Other common motor types may not have any type
of switch and instead use a capacitor permanently connected to one
winding to shift the phase. These motors would also need the 1/2
frequency.
The reason for the 1/2 frequency is that the speed of most
induction motors depends on frequency. If the voltage is lowered the
motor will start to slow and will then consume more current in an
effort to speed back up to normal operating speed. If the voltage gets
too low the motor will just stall and then will overheat and
eventually burn up if the power supply can deliver enough current.
This stalling will happen way before the motor drops to 1/2 speed.
Shaded pole induction motors are controllable to some extent by
lowering the voltage. These motors are not very efficient. They are
mostly used for applications requiring little torque, like the
turntable in a microwave oven.
Shaded pole motors are sometimes used for fans and controls for
these can be bought at any store that sells home improvement stuff.
Shaded pole motors have a tiny starting torque and so are not
practical for anything other than starting very light loads, such as
fans and turntables. Their speed regulation is also poor as it is
quite sensitive to load changes.
Unfortunately there is no simple way to lower by 1/2 the speed of a
typical single phase induction motor.
Eric