# Eddy Currents in a disc

## Main Question or Discussion Point

I have read that locomotives use eddy current braking systems, and one article mentioned that this system has also been used to charge batteries in a recovery circuit. However, I can not find details on this idea. From what I understand, the train has conducting discs attached to the wheels, and an electromagnet is charged in close proximity to the disc producing a powerful torque via the eddy currents produced in the disc. How could a system recover electric current from this disc, I thought most if not all the force is converted to heat in the disc. Anyone have any ideas?

Thanks!
G

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I have read that locomotives use eddy current braking systems, and one article mentioned that this system has also been used to charge batteries in a recovery circuit. However, I can not find details on this idea. From what I understand, the train has conducting discs attached to the wheels, and an electromagnet is charged in close proximity to the disc producing a powerful torque via the eddy currents produced in the disc. How could a system recover electric current from this disc, I thought most if not all the force is converted to heat in the disc. Anyone have any ideas?

Thanks!
G
Instead of thinking about "eddy currents" where a conductor moving in a magnetic field creates a circulating current that creates a force opposing the motion make the system more formal. In most "eddy current" systems motion induces a current that flows around in a conductor (in "eddies") and except for the forces created the current is just wasted heating the conductor. But what you are really doing is building a generator that is powering a load so it develops a mechanical force opposing it's mechanical input. In a more formal system we'd use a REAL generator. Now that would be built so as to direct the generated current into external wires rather than just round and round in the conductive parts. And then as a load you might use a large resistor, but better would be a bank of batteries that need charging! Hence if you want to slow the train (or Toyota Prius) you hook the battery pack to the generators on the wheels which provide a slowing torque and at the same dime produce an electric current which is charging the batteries. This way much of the energy needed to slow the vehicle is save to be used again in speeding it back up! Clever!

Instead of thinking about "eddy currents" where a conductor moving in a magnetic field creates a circulating current that creates a force opposing the motion make the system more formal. In most "eddy current" systems motion induces a current that flows around in a conductor (in "eddies") and except for the forces created the current is just wasted heating the conductor. But what you are really doing is building a generator that is powering a load so it develops a mechanical force opposing it's mechanical input. In a more formal system we'd use a REAL generator. Now that would be built so as to direct the generated current into external wires rather than just round and round in the conductive parts. And then as a load you might use a large resistor, but better would be a bank of batteries that need charging! Hence if you want to slow the train (or Toyota Prius) you hook the battery pack to the generators on the wheels which provide a slowing torque and at the same dime produce an electric current which is charging the batteries. This way much of the energy needed to slow the vehicle is save to be used again in speeding it back up! Clever!
Yes I see, but what I'm trying to understand is this... In the example, the train uses a solid conducting disc attached to the wheels. how would you capture the electricity from a disc like this. I can understand using a series of coils arranged in a circular fashion around the wheel, with a commutator/brush to connect the ends of the coils, but how would you do this in a solid disc? The disc is uniform, so where would you tap the disc to capture the electrical energy? Would you simply place a brush at the perimeter and the center of the disc?

Thanks!