Page 13 - PortescapCatalog 0212_V012021Eng

Back EMF is a voltage generated by the windings of a permanent magnet motor in rotation. Because this
voltage increases with speed and is applied in the opposite direction from the input voltage, the back EMF
constant can be used to calculate the motor’s speed at any given input voltage, assuming no friction and no
Back EMF constant loading torque.

The specification document also gives the 0-peak value of the back EMF, which is typically higher than the
average value and can be measured on motor phases with an oscilloscope while the motor is back-driven.

Torque constant This value relates the current in the motor phases to the torque created at the rotor level.

2
This value gives the extra joule losses in the motor winding, in watts, multiplied by the torque squared (Nm ).
Motor regulation R/k 2 A lower number indicates a better magnetic design for dealing with high torques. The calculation is based on
internal phase resistance, not including wire soldering and connector resistance.

This is simply another way of expressing the previous property. In this case, a higher number indicates a more
Motor regulation k/R 1/2 efficient magnetic design for dealing with high torques.

This is the coil phase resistance measured at room temperature before the coil is soldered to the motor circuit
Internal resistance - phase to phase
assembly.

This is the phase resistance measured for the completed motor at room temperature. It includes solder, wire
Line to line resistance at connectors and (if present) connector resistances. In motors with very low resistance, the line to line resistance may differ
significantly from the internal resistance.

Inductance - phase to phase This is the motor phase inductance measured with an inductance meter at 1000 Hz.

This represents the motor’s ability to accelerate quickly at a given voltage and without any current limitation.
Mechanical time constant
It typically represents the time needed to reach 63.2% of the motor’s final speed under a constant voltage.

This is the time constant L/R (inductance divided by resistance) that is needed to properly size the driver
Electrical time constant PWM frequency. It represents the motor’s ability to let the current vary quickly. This value is commonly very
low in slotless BLDC motors.

V012021 • © 2021 Portescap. Specifications subject to change without notice. 13