The torque vs. speed and output power curves depend on the supplyn voltage to the motor.
The supply voltage to the motor assumes continuous running of the motor at an ambient temperature of 20°C in nominal operational conditions.
It is possible to supply the motor with a different voltage (normally between -50% and + 100% of the recommended supply voltage).
If a lower voltage is used compared to the recommended supply the motor will be less powerful.
If a higher voltage is used, the motor will have a higher output power but will run hotter (intermittent operation is recommended).
For variations in supply voltage between approximately - 25% to + 50%, the new torque vs. speed graph will remain parallel to the previous one.
Its start-up torque and no-load speed will vary by the same percentage (n%) as the variation in supply voltage. The maximum output power is
multiplied by (1 + n%)2.
Example : For a 20% increase in supply voltage
Start-up torque increases by 20% ( x 1.2)
No-load speed increases by 20% ( x 1.2)
Output power increases by 44% ( x 1.44)

The graph for this relationship does not vary with the supply voltage of the motor. The end of the curve is extended in accordance with the torque
and the start-up current.
The gradient of this curve is called the «torque constant» of the motor.
Kc = Cd
Id - Io
This torque constant is such that :
C = Kc (I - Io)
The «rotational friction torque» is Kc Io.
The torque is therefore expressed as follows :
C = Kc I - Cf with Cf = Kc Io
Kc = Torque constant (Nm/A)
C = Torque (Nm)
Cd= Start-up Torque (Nm)
Cf = Rotational friction torque (Nm)
I = Current (A)
Io = No-load current (A)
Id = Start-up current (A)
The graph of torque vs. current and torque vs. speed is used to determine