Figure shows the motor characteristic of a externally-excited direct-current motor.
In the low speed range, the motor is driven with a variable armature voltage and a constant torque. Above the corner speed, field weakening with a constant power output is employed. Theoretically a starting clutch could be left out. In practice, however, due to the required large current-control area, clutches are used without exception. Series-wound machines distinguish themselves through their robustness and simplicity but are disadvantageous form the point of view of their control since the entire working flow has to be led over the control equipment in order to vary the speed. Regenerative braking and the reversal of the running-direction require expensive mechanical alterations.