Motor Drive Questions

[arocon]

I know the torque of an Induction motor. Now I need to calculate the current. What is the best way to do it so that it can express in software ? I have seen , Current = torque * 1/(torque constant) * gravitational acceleration . Could anyone clear me what is gravitational acceleration ? Also how to find out torque constant ?

 

[DickDV]

You will need to know the magnetizing current of the motor. It is the actual current drawn when the motor is at no-load. Or, the manufacturer can provide it. And you know the full load amps from the motor nameplate.

Set up a vector triangle with the magnetizing current on one side and the full load current as the hypotenuse. Solve for the remaining side which is the full load torque producing current.

This is the torque producing current at full load torque. It is directly proportional to actual torque. So, given the actual torque, find the actual torque producing amps. Using the Pythagoreon Theorem again, use the known magnetizing amps as one side, the actual torque producing amps as the other side, and solve for total amps (the hypotenuse). That is the total amps under reduced torque conditions.

 

[Tom Jenkins]

I usually just get the motor data sheet. It will usually provide amps at full, 3/4, 1/2 and no load.

Gravitational acceleration "g" is 32.2 ft./s/s or 9.81 m/s/s on this planet.

I think you are getting yourself into a calculation more complicated than you need, and usually g doesn't enter into the kind of calculation you are doing. What exactly are you trying to accomplish?