Universal AC motor torque calculation

[valdorf]

Hello,

I have AC universal motor and I would like to calculate motor load torque.
I have power metering IC and I can measure current, voltage and power of motor circuit. Also I have motor speed feedback.
Please let me know if it is enough to calculate aprox. motor load torque, using equation T=P/w=IU/w (where T - motor load troque, P - power, w - motor speed). Could I use this equation to get a directly relationship of torque? Do I need to measure additional parameters or use different equation?

This is basic DC brushed motor equation, so as I understand torque depends on motor characteristic and I need to use motor constant.

Thank you for your answers.

 

[FvM]

Your equation isn't specific to universal or brushed motors, but should generally work. For better accuracy, you can substract resistive losses (I²R) and apply a efficiency factor that takes account of mechanical losses.

Referring to specific equations of series wound motor, torque is proportional to squared current. The proportional constant need to be determined however, and saturation restricts the validity of this relation.