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What's the percentage won back thru regenerative breaking?..

Discussion in 'Technical' started by voyager, Oct 8, 2016.

  1. voyager

    voyager Member

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    In the typical Model S, in daily practice.
    Wikipedia says that 80% would be theoretically possible.

    As regards electric cars, the DoE explains that the efficiency between the electric motor and the wheels amounts to 60%.

    Let us consider the electric motor efficiency {\displaystyle \eta _{eng}=0.6}[​IMG] and the braking proportion in towns {\displaystyle p=0.46}[​IMG]and on motorways {\displaystyle p=0.1}[​IMG].

    Let us introduce {\displaystyle \eta _{recup}}[​IMG] which is the recuperated proportion of braking energy. Theoretically, it can reach up to 80%.
     
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  2. voyager

    voyager Member

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    I take it that it will be not the ideal 80%... So what is it in real life?
     
  3. LastGas

    LastGas Member

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    #3 LastGas, Oct 9, 2016
    Last edited: Oct 9, 2016
    But after you recover that kinetic energy, you have to convert it back to kinetic energy again to make the car go. Coasting is good. Braking is evil.

    I'm hoping that the less aggressive TACC braking of 8.0 over 7.1 will give some reduction in energy consumption.
     
  4. Johan

    Johan Took a TSLA bear test. Came back negative.

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    Below 40%, for sure, this is "full round-trip from battery back to battery" considered. There are scientific papers on this.
     
  5. swaltner

    swaltner Member

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    Here's a rough calculation based on the info presented on my LEAF's dashboard. It says that if I slow down using regenerative braking from 65 mph to 25 mph, turn the corner, I can then accelerate to about 50 mph using the recaptured energy.

    From high school physics: KineticEnergy = 1/2 Mass Velocity^2; The car doesn't change mass, so you can compare the energy by just comparing the Velocity^2.

    Before Slowing Down: energy = 65*65 = 4225
    While Turning: energy = 25*25 = 625
    After Accelerating: energy = 50*50 = 2500

    To figure out the round trip efficiency, we compare the kinetic energy that was removed during the braking process to the kinetic energy added during the acceleration.

    Kinetic energy of the car is reduced by 3,600 (4225 - 625) and then raised by 1875 (2500 - 625). In this case, I got 52% (which is 1875/3600) round trip efficiency on the deceleration/acceleration. These are just the numbers that I remember off the top of my head and also are not in any kind of a controlled environment. Also note that how heavy you press on the accelerator pedal has an impact on the round trip efficiency.

    As @LastGas mentions, it would be more efficient to simply coast and not use the regenerative braking. If it was in the Atom, I could take the corner at 55 mph and not need to brake/accelerate.
     
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