# Is Motor KT Linear with current?

This may be a little basic for some. Sorry in advance...

I would like to use a large 3ph motor to perform a fast, controlled, stop.

The rated motor torque is 850Nm @ 242A.

My inverter claims to be able to deliver a short duration current of 460A.

Calculating the torque constant KT = 3.51Nm/A (from the rated figures 850/242 = 3.51)

Could I realistically expect 460A x 3.51Nm/A = 1615Nm of reverse torque for a short duration?

Or in fact, like when a motor is starting would the ratio of current to torque be a non-linear relationship?

(The motor would be running at normal load and speed and then attempt to decelerate as fast as possible.)

• What kind of motor?
– Eric
Commented Mar 20, 2015 at 12:10
• Since KT is the torque constant it's supposed to be constant, not linear with current but independent of it. As JonRB says, however, if the magnetic circuit saturates you may see Kt decrease, i.e. torque increase less than expected. This is a question for the motor manufacturer if his datasheet doesn't cover performance above rated current.
– user16324
Commented Mar 20, 2015 at 14:10