When battery is full, where does regen power go?

Discussion in 'Prius v Technical Discussion' started by JasonW, Dec 20, 2013.

  1. JasonW

    JasonW Junior Member

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    Ok so here's a question. Lightly pushing on the brakes, engages the electric motor to create (regenerate) power that goes into the battery. This creates resistance in the wheels, and slows the vehicle... the more power you are regenerating, the more resistance is applied to the wheels. Got it.

    So what happens when the battery is full? If the power has nowhere to go, (no need for it), then you should get no resistance on the wheels. I realize of course that the disc brakes can engage, but from what I feel when driving the car, the regeneration function always seems to be working. So is there a big resister array that burns off the spare electrical energy (like they have in trains to slow them down)? Or does the car simply just use the brake pads, and I'm just not noticing it?

    -Jason
     
  2. rjparker

    rjparker Senior Member

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    You answered your own question. The brakes are used closer to 100%, when and if the battery was "full". That's one reason why you have the "B" gear, it provides engine braking without regard to the battery being full to help save the brakes. On the other hand, most get over 100k on their brakes since they do little work compared to conventional cars.
     
  3. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    If indeed the HV Battery is 'full' in the opinion of the computers, then the engine will be used similar to a "Jake Brake" to help slow the car. When that happens the harder you hit the brake, the faster the engine goes.
    Engine braking - Wikipedia, the free encyclopedia
     
  4. GrumpyCabbie

    GrumpyCabbie Senior Member

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    And when the battery is indicated as 'full' it probably is far from it.
     
  5. miscrms

    miscrms Plug Envious Member

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    My understanding is that even if you don't manually select B mode, at some preset battery SOC (state of charge) level the controller will automatically apply it to prevent the battery from overcharging. B mode is like engine braking in a traditional vehicle, but with one major difference. The ICE is not directly coupled to the wheels, so just closing the valves to create engine pumping/vacuum resistance would not slow the vehicle by itself. Instead MG2, which is directly connected to the wheels is still creating resistance through regenerative braking, but MG1 is used to crank the ICE to dissipate the energy being generated by MG2. So the ICE becomes a mechanical resistance element to load MG2, which becomes an electrical resistance element to load MG1, which in turn becomes a mechanical resistance element to slow the vehicle.
     
  6. fdret44

    fdret44 Junior Member

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    The real difference between pressing on the brake and the "B" mode is that the engine is being turned to dissipate some of the energy and it will take longer before the battery reaches the "full" state. I have found the "B" mode to be most useful when going down a long steep hill. "B" mode seems to work the same in my "V" as it does in my 2004 Prius.
     
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