11-09-2017, 01:27 PM
A eddy current brake, such as a conventional friction brake, is a device used to retard or stop a moving object by dissipating its kinetic energy as heat. However, unlike electromechanical brakes, where the drag force used to stop the moving object is provided by friction between two pressed surfaces together, the drag force in a eddy current brake is an electromagnetic force between a magnet and a nearby conductive object in relative motion, due to the parasitic currents induced in the conductor through electromagnetic induction.
A conductive surface passing through a stationary magnet will have circular electrical currents called parasitic currents induced therein by the magnetic field, as described in the Faraday induction law. According to Lenz's law, the circulating currents will create their own magnetic field opposing the field of the magnet. Thus, the moving driver will experience a pulling force of the magnet that opposes its movement, proportional to its speed. The electrical energy of the parasitic currents dissipates as heat due to the electrical resistance of the conductor.
In a eddy current brake, the magnetic field can be created by a permanent magnet or an electromagnet so that the braking force can be activated and deactivated or varied by varying the electric current in the electromagnet windings. Another advantage is that since the brake does not work by friction, there are no surfaces of brake shoes that wear out, requiring replacement, just like friction brakes. A disadvantage is that, since the braking force is proportional to the speed, the brake has no clamping force when the moving object is stopped, as provided by static friction in a friction brake, so that in vehicles it must be complemented by a friction brake. Foucault current brakes are used to reduce high-speed trains and roller coasters, to stop power tools quickly when power is turned off, and on electric meters used by power companies.
A conductive surface passing through a stationary magnet will have circular electrical currents called parasitic currents induced therein by the magnetic field, as described in the Faraday induction law. According to Lenz's law, the circulating currents will create their own magnetic field opposing the field of the magnet. Thus, the moving driver will experience a pulling force of the magnet that opposes its movement, proportional to its speed. The electrical energy of the parasitic currents dissipates as heat due to the electrical resistance of the conductor.
In a eddy current brake, the magnetic field can be created by a permanent magnet or an electromagnet so that the braking force can be activated and deactivated or varied by varying the electric current in the electromagnet windings. Another advantage is that since the brake does not work by friction, there are no surfaces of brake shoes that wear out, requiring replacement, just like friction brakes. A disadvantage is that, since the braking force is proportional to the speed, the brake has no clamping force when the moving object is stopped, as provided by static friction in a friction brake, so that in vehicles it must be complemented by a friction brake. Foucault current brakes are used to reduce high-speed trains and roller coasters, to stop power tools quickly when power is turned off, and on electric meters used by power companies.