Back then, 90V dc motors were controlled by SCRs. Nowadays, some of them are PWM-controlled. Basically my question is:
120VAC rectified and filtered are about 170VDC. For a 90VDC motor, this is too much. The idea on this is controlling the duty cycle under 50%?

 

All you have to do is monitor the rpm if concerned, and control accordingly.
Also current limit is a good idea, usually you can achieve this on a PWM or SCR drive.
Max.

 

You could full-wave rectify the mains with no capacitor smoothing (120Vdc), then add a small resistance – dropping the 30V or so, if required.

 

Back then, 90V dc motors were controlled by SCRs. Nowadays, some of them are PWM-controlled. Basically my question is:
120VAC rectified and filtered are about 170VDC. For a 90VDC motor, this is too much. The idea on this is controlling the duty cycle under 50%?

Hello, Xavier. You may find this thread interesting. The good stuff is after post #170