[Christ]

Originally Posted by MPaulHolmes

I don't think it works that way. I've been thinking about this all day! It has given me a headache, and here's what I think I know:

The Torque-RPM curve is approximately a straight line for a DC motor. At 0 rpm, the torque is highest, and at max rpm, the torque is 0.

At 240v, the MAX rpm is 2 times the MAX rpm at 120v. Also, at 20 amps, the MAX torque is 2 times the MAX torque at 10 amps. So, I attached a picture of the graph of the torque-rpm lines for 120v @ 20amps and 240v @ 10amps.

In the picture, w120 is the max rpm at 120 volts, and T10 is the torque at 10 amps (2*T10 is the MAX torque at 20 amps and 2*w120 is the MAX rpm at 240 volts). Their rate of rotation and torque are the same at one point, when the RPM is 2/3 of w120 (algebra! Find where 2 lines cross! hahaha!)

There are some torques that the higher voltage setting just can't match, and some speeds the higher current setting can't match.

Oops... forgot to specify - I was asking about AC motors... dunno if that makes a difference.