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Recharging Electric Cars?

  1. Aug 3, 2012 #1
    Just out of curiosity, electric cars produce movement through converting electrical energy into kinetic via magnetic field and magnets, etc; would it not be possible to convert the kinetic energy back into electrical energy while the car is moving. I know the Law of Conservation of Energy says that all sums of energy must be the same both before and after, but if a generator were to be placed to use the kinetic energy acting upon to car to convert it to electrical energy could you not convert most of the kinetic energy back into electrical energy while the car still moves. Sorry i dont know if ive explained it very well. Basically im asking unless the generator slowed the rotational force placed upon the axle down how come you cant double the energy?
  2. jcsd
  3. Aug 3, 2012 #2


    Staff: Mentor

    Yes, that is how regenerative breaking works in today's hybrid cars. Except you can't increase the energy, you always get back less than you put in.
  4. Aug 4, 2012 #3
    So the act of using the rotational force of an axle like generator slows it down? What about if they were to channel air through a car and use the force and pressure of the air to spin a generator would they be able to recover the kinetic energy spent in moving the car forward and gather it up again? Sorry if i sound stupid, I'm just trying to think of ways that we could like use energy more efficiently.
    Last edited: Aug 4, 2012
  5. Aug 4, 2012 #4


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    Using a windmill to extract energy from the air passing through/over a car would increase drag, meaning more energy is required to push the car through the air. More energy than you capture with the windmill. There would also be losses in the generator. Overall you are better off not using a wind mill and concentrating on reducing drag.

    There are times when you want to slow down. A cars brakes waste all the KE the car has gained by turning it into heat. However instead of brakes you can connect a dynamo to the wheels and collect the energy...


    a.k.a. KERS See also Formula 1 racing cars

    The extra load of the dynamo/generator acts like a brake and slows down the car.
  6. Aug 4, 2012 #5


    Staff: Mentor

    Yes, it slows it down, as does any means of extracting KE. However, it is more efficient than throwing the energy away in the brakes. That is why all hybrid vehicles use the idea.
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