Back EMF

Back Electro-motive Force is the voltage generated during the operation of a rotating machine (a generator or a motor). When voltage (an electro-motive force) is applied to a motor's armature, it begins to rotate, and an amount of electrical resistance is generated by the rotating magnetic field. This kick-back is called Back Electro-motive Force or Back-EMF ( BEMF ).

BEMF is proportional to speed and independent of load. It produces a counterforce that limits the speed of the motor. The faster the armature turns, the more BEMF is produced.

Dimensions for the BEMF can be

• "Volts per thousand RPM," or "Volts/krpm"
• "Volts/(rad/sec)" where (rad/sec) is Radians per Second.