Eddy current brakes

An eddy current brake, like a conventional friction brake, is a device used to slow or stop a moving object by dissipating its kinetic energy as heat. However, unlike electro-mechanical brakes, in which the drag force used to stop the moving object is provided by friction between two surfaces pressed together, the drag force in an eddy current brake is an electromagnetic force between a magnet and a nearby conductive object in relative motion, due to eddy currents induced in the conductor through electromagnetic induction.

A conductive surface moving past a stationary magnet will have circular electric currents called eddy currents induced in it by the magnetic field, as described by Faraday's law of induction. By Lenz's law, the circulating currents will create their own magnetic field which opposes the field of the magnet. Thus the moving conductor will experience a drag force from the magnet that opposes its motion, proportional to its velocity. The electrical energy of the eddy currents is dissipated as heat due to the electrical resistance of the conductor.

In an eddy current brake the magnetic field may be created by a permanent magnet, or an electromagnet so the braking force can be turned on and off or varied by varying the electric current in the electromagnet's windings. Another advantage is that since the brake does not work by friction, there are no brake shoe surfaces to wear out, necessitating replacement, as with friction brakes. A disadvantage is that since the braking force is proportional to velocity the brake has no holding force when the moving object is stationary, as is provided by static friction in a friction brake, so in vehicles it must be supplemented by a friction brake.

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