Back EMF: The voltage generated when a permanent magnet motor is rotated. This voltage is proportional to motor speed and is present regardless of whether the motor winding(s) are energized or de-energized.

Back End of A Motor: The back end of a normal motor is the end that carries the coupling or driving pulley (NA). This is sometimes called the drive end (D.E.), pulley end (P.E.) etc.

Base Speed, RPM: The speed in revolutions per minute (RPM) which a DC motor develops at rated armature and field voltage with rated load applied.

Bearing Life: Rating life, L10 (B10), is the life in hours or revolutions in which 90% of the bearings selected will obtain or exceed. Median life (average life), L50 (B50), is the life in hours or revolutions in which 50% of the bearings selected will obtain or exceed.

Bearings: Bearings reduce friction and wear while supporting rotating elements. When used in a motor, they must provide a relatively rigid support for the output shaft. Bearings act as the connection point between the rotating and stationary elements of a motor. There are various types such as roller, ball, sleeve (journal) and needle. Ball bearings are used in virtually all types and sizes of electric motors. They exhibit low friction loss, are suited for high-speed operation and are compatible with a wide range of temperatures. There are various types of ball bearings such as open, single shielded and sealed.

Bifilar Winding: Indicates two distinct windings in the same physical arrangement; these windings are usually wired together, either in series or in parallel, to form one phase.

Bipolar Chopper Driver: A class of step motor driver which uses a switch mode (chopper) technique to control motor current and polarity. Bipolar indicates the capability of providing motor phase current of either polarity (+ or -).

Brakes: An external device or accessory that brings a running motor to a standstill and/or holds a load. Can be added to a motor or incorporated as part of it.

Breakaway Torque: The torque required to start a machine in motion. Almost always greater than the running torque.

Breakdown Torque: The maximum torque a motor will develop at rated voltage without a relatively abrupt drop or loss in speed.

Brushless Motor: Class of motors that operate using electronic commutation of phase currents, rather than electromechanical (brush-type) commutation. Brushless motors typically have a permanent magnet rotor and a wound stator.


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