# Modern applications of electromagnetism -- Regenerative Braking

## Homework Statement

Can someone explain what regenerative breaking is?

## Homework Equations

no equations required

## The Attempt at a Solution

I understand that this occurs with electric cars. It uses the idea that the electric motor and the electric generator are so similar. But how does the electric motor that is causing the wheels to turn, transform into an electric generator that produces energy to recharge the battery and start the electric car going again.
I just need a clear explanation of what "regenerative breaking" is?

#### Attachments

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Borg
Gold Member
In regenerative braking, the motor is just functioning as a generator of electricity when you brake. Consider the motors at a hydroelectic power plant.
The water from a dam flows through the turbines and the motors generate electricity. This is equivalent to the car example when the moving car is forcing the generator to turn and the generated electricity is stored in the battery.

You could theoretically reverse the process in a hydroelectric plant by supplying electricity to the motors and force the water uphill. This is similar to the motors a car being supplied electricity from the battery to force the car to move.

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epenguin
Homework Helper
Gold Member
I think routinely many times a minute say in London or other Metropolitan transport systems, the trains are doing this. Having taken all the energy to build up a speed after going only a very few km they do not waste all that kinetic energy with mechanical brakes turning it into heat; rather they feed it back into the source. So as a train slows down a generator rotor somewhere else will be speeding up.

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great explanation! :)