Constant Torque Motor

[controlnovice]

Thanks for your answers to my earlier questions on Constant vs Variable Torque motors.

I've tried to find info on the net for current curves for Constant Torque motors.

Our possible situation: We are at 100% speed and the load is 'drawing' full torque of the motor. Our kW or amp alarm (set below the overload trip point) goes off indicating the material is becoming more viscous(this is on an agitator).

Will slowing the motor help us run longer without tripping? By looking at the Torque vs speed curves, we can maintain the same mixing by reducing the speed, but are we really reducing the current and thus able to 'save' from tripping the motor?

 

[Barry1961]

I would think that the torque would decrease some as the speed of the mixer blades decreased. This should reduce power and allow the motor to run within its range.

Even if the torque stayed the same and only the speed decreased it would be a decrease in power.

Current can be deceiving when using VDF’s, in particular at high and low speeds, so I like to think of power.

Barry1961

 

[Marke]

Hello controlnovice

If a reduction in speed reduces the torque requirement, then a speed reduction would reduc the motor heating. If the speed reduction does not reduce the torque, then the KW input will reduce, but the KW rating of the motor will also reduce and you will be no better off.
The motor KW rating reduces with speed when using a variable speed controller.
You could look at slowing the blades and keeping the motor at the same speed. This would reduce power output from the motor without changing it's rating.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[Barry1961]

Reducing the speed should keep the motor from tripping.

With constant torque and reduced hertz/speed the voltage will decrease in a fairly proportional and linear fashion. From my experience testing different drives the current will drop a small amount 5%-10% when the hertz are reduced below the rated hertz by 20%, it then holds steady. This current reading was generated by the drive though and I am not sure how accurate it really is.

I would think that most overload devices or overload algorithms in drives would by power/watt dependant instead of just current dependant. This might be a good question for another post.

Barry1961