# Voltage, Current, Angular Velocity, and the effect they have on Torque

I've come across the equation VI = Tw (voltage times current is equal to torque times angular velocity); because power in (voltage and current) is equal to power out (torque and angular velocity). This equation can be changed to T = (V*I)/w. This shows me that an increase in current AND voltage would create an increase in torque; and that a decrease in angular velocity would create an increase in torque. Am I right? Or do I just not understand this stuff at all?

I'm trying to figure out how to create the greatest torque possible WITHOUT changing the other physical properties of the electric motor.

• Are you trying to design a motor for maximum torque, or use an existing motor? What sort of motor is it? (eg. 3 phase induction, permanent magnet brushed DC). Jul 12, 2016 at 21:48
• Designing a motor. Jul 13, 2016 at 22:10

Torque is directly proportional to current. One of the motor specifications is the torque constant, Kt.

Torque = Kt * current

The voltage and angular velocity play only an indirect role. The voltage is what creates the current, and the angular velocity creates the BEMF that reduces the available voltage (thereby reducing the current, which then reduces the torque).

As a demonstration, take a motor, push a voltage through it with no load, and it will accelerate to a speed where the back-EMF balances the input voltage. You have little torque, and also not a lot of current. Now try to slow the motor down. As you do, the back-EMF drops, allowing more voltage to drive the motor, increasing the current and the torque. The motor is fighting you to keep spinning, and that requires more current.

If you use a current-mode amplifier to drive the motor, you can directly control torque, without regard for the voltage.

This is true for all motors: brushed, brushless, induction, permanent magnet, or stepper.

You should write what kind of motor you have and if you have a controller/the control scheme.

if you have a dc motor with permanent magnets, then the max torque is going to be at zero speed, but since you should not use the starting torque in steady state the max torque is the nominal of your motor.

to obtain it let your motor turn slow and give it its nominal current (i.e. as much ''input power'' as you can).

This is a ''from the books'' answer, if you are going to actually implement a solution wait for someone more qualified. I'm sure you'd end up burning everything with my advices.

if you have not a dc motor then you need vector control to obtain the maximum torque per ampere. which is quite a vast topic.