Hi, I have built this motor speed controller to control a PMDC motor on the power feed I made for my mill, it works very well driving a geared motor from an old rechargeable drill..

Unfortunately I have already built my power feed system using a PMDC motor from an old main frame computer tape drive system. The motor is much higher voltage and runs without apparent stress from a 72volt supply. I would appreciate comments on this modification to the drive system to handle the higher voltage.

The modifications are marked in the red squares.