[GreenKeys] [External] Re: Need motor for 50Hz supply (or DC)

[Jones, Douglas W]

From: John Lawson via GreenKeys <greenkeys at mailman.qth.net> -- Thursday, September 3, 2026 3:43 PM
> Many sync motors (60htz) will run on 50 htz, but the heat disspation goes up.

To maintain something approximating constant torque when you change the frequency, you should keep the voltage to frequency ratio constant.  So, when running a 60Hz 120V motor at 50Hz, reduce the voltage to 100V.

The  no-load speed will remain close to synchronous, of course, so you still need new gearing if you want to use the motor to maintain something at a set speed.  And, since power is proportional to speed times torque, your reduced speed also translates to reduced power.

However, the voltage reduction I described keeps the peak current through the motor windings roughly the same.  If you run that motor at 50Hz and 120V, you'll have peak currents comparable to running it at 60Hz 144V.  Do that and the motor current will go up, leading to more resistive loss and a hotter motor.

            Doug Jones