A homopolar motor is a commutatorless DC motor based on the unipolar induction. The motor rotates along a fixed axis, which is parallel to the magnetic field of a permanent magnet. Homopolar intended to indicate that is not commutated power. Such motors consist necessarily of a single current loop. Since these motors can generate only small torques, technical application is severely limited.


The homopolar motor is driven by the Lorentz force. This occurs when the charge carriers migrate on the way to the middle of the axis of rotation through the magnetic field generated by the small magnet and are deflected. Since the field lines of the magnetic field and the rotation axis is always pointing in the same direction, the motor rotates without commutation. The advantage of simplicity zunichtegemacht by the disadvantage of the small torque. Like many other electric machines of the homopolar motor is reversible. It can no rectifier and without commutator generate a DC voltage, when the rotational axis is rotated mechanically, and is referred to as Unipolargenerator.


First structures were demonstrated by Michael Faraday in 1821 at the Royal Institution of London. Another historic design this type of motor is referred to as Barlow wheel.


The homopolar motor can be easily reconstructed. A permanent magnet generating an external magnetic field, and a battery generating the electric power. The magnet does not necessarily move along or be in contact with the axis of rotation. Its only purpose is to generate the magnetic field.


Homopolar motor 2D

Magnetic field lines and Lorentz force on homopolar motor