AC Motor In Reverse

Main Question or Discussion Point

Say I have an AC motor with 100 ft*lbs torque, and I run it against a load of 200 ft*lbs torque so that the motor spins in the opposite direction of the power it is providing. Is this possible, and if so can this condition be sustained over a period of time without damaging the motor?

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gerbi
Gold Member
Say I have an AC motor with 100 ft*lbs torque, and I run it against a load of 200 ft*lbs torque so that the motor spins in the opposite direction of the power it is providing. Is this possible, and if so can this condition be sustained over a period of time without damaging the motor?
You are talking about nominal torque of AC motor ? If so, there is also a parameter called critical or maximal torque. It's bigger than nominal torque so the motor can work properly (stabile work) up to the maximal torque. The power drain will be increased, motor may be overheated.

It all depends what kind of load is that, is it a static load, a fan-type or some other. Other important thing is are You starting your motor or just adding load to spinning machine.

In worst case - rotor spinning in opposite directoion to the field - It would damage the motor rather quickly.

I may have misunderstood, but it looks like what you are calling a "load" is actually something that is adding energy to the system. If you really connect a motor capable of 100 ft*lbs torque to a load that requires 200 ft*lbs torque, then the motor will simply stop because it couldn't produce the required torque to turn the shaft of that load. But if I've misunderstood, and the thing you call a "load" is actually pushing the motor in the opposite direction, then by definition you probably shouldn't call that a "load". Rather, it would be some device like a motor which produces 200ft*lbs of torque (in the opposite direction of the first motor) and would, therefore, have to get that energy from some other source--because energy is of course conserved.