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Braking. What happens after the battery is full?

Discussion in 'Gen 2 Prius Main Forum' started by rposton, Mar 21, 2006.

  1. rposton

    rposton Member

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    From what I have read in other threads in this forum, D captures more kenetic energy than B, and sends it to the battery. The purpose of B is when the downhill is so long that your foot might get tired pressing the brake pedal. Since such a hill would max out the battery, the ICE is used to help control the downhill speed of the car. Also, friction brake comes into play at about 10 mph and less.

    Therefore, my question is...

    You go down a long hill in D, and your battery bars max out to the top, and you are traveling, lets say 50 mph, what does the car do with your extra kenetic energy? Does it,
    1. start using more of the friction brake?
    2. spin up the ICE and use it even though you are still in D?
    3. somehow change the excess kenetic energy into heat energy and dump it into the coolant, which then can be used to warm the cabin, or wasted via. the radiator?
     
    #1 rposton, Mar 21, 2006
  2. kkister1492

    kkister1492 New Member

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    The ICE will engage to use up the extra charge. This happened quite a lot on our trip in the Rocky Mountains last year.
     
    #2 kkister1492, Mar 21, 2006
  3. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    you will stop charging the battery and start using your friction brakes more
     
    #3 DaveinOlyWA, Mar 21, 2006
  4. efusco

    efusco Moderator Emeritus
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    Yup, it's pretty dramatic actually. I experienced an 80% SOC twice this past week and was able to watch the ICE spin up to over 3000 RPM and the amerage drop to -1 while braking on a downhill! I tried releasing the brake and reapplying to see if I could get the regenerative brakes to reingage to absolutely no avail. The ECU will go to some pretty extreme measures to prevent any overcharge even at the expense of lower fuel economy.
     
    #4 efusco, Mar 21, 2006
  5. hyo silver

    hyo silver Awaaaaay

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    Going up a big hill in summer, I drive a little slower, and turn off the air conditioning. Going down a big hill, I drive a little faster and crank up the cooling to take advantage of the 'free' electricity. This gets tedious on low rolling hills, but in mountain passes it seems to help the efficiency. (My daughter tried to apply this technique to the music volume, but I don't think it has the same effect. :) )

    I love the regenerative brakes. No more warped discs for me!
     
    #5 hyo silver, Mar 21, 2006
  6. rposton

    rposton Member

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    I like the idea about wasting excess electricity into the music.

    The Prius has enough, but it would be nice to add a way to, once the battery is full, to store additional electricity as extra heat in the coolant on less than 45 degree days, and then circulate it through the engine and heater core of the car.

    I guess somebody, not me, could convert the roof to an airbrake, like on the back of an F15 Eagle.

    Thanks for the replies. I learned something.

    -Roy Poston
     
    #6 rposton, Mar 22, 2006
  7. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    man i agree 100 %. i have had situations when i am maxed out on a charge, still got a ¼ mile of downhill left, and my CANVIEW says im DRAINING the traction battery!!!

    man i HATE THAT. whats worse, since doing the 50P update, my max SOC seems to only be 75% now...anyone else notice this??
     
    #7 DaveinOlyWA, Mar 22, 2006
  8. SirGreen

    SirGreen New Member

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    I think I would turn up the AC or the heat.
     
    #8 SirGreen, Mar 22, 2006
  9. DaveinOlyWA

    DaveinOlyWA 3rd Time was Solariffic!!

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    not me... but i do plug in the ipod, laptop, cellphone....
     
    #9 DaveinOlyWA, Mar 22, 2006
  10. rbarline

    rbarline Junior Member

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    How can an ICE engine use up any charge? I don't think ICEs can do that. There must be a better explanation.:)
     
    #10 rbarline, Oct 15, 2009
  11. qbee42

    qbee42 My other car is a boat

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    MG1 spins the ICE as a big air pump. Moving air creates friction, which burns up energy as heat.

    Tom
     
    #11 qbee42, Oct 15, 2009
  12. David Beale

    David Beale Senior Member

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    Tom is correct. It doesn't "waste fuel". It DOES use friction brakes more if you are applying the brake (fully friction brake once you reach what the car considers full allowed charge). It also uses EV further up the accelerator pedal travel. The engine is spun with no fuel injected to "dump" excess charge.

    Next time you are descending a long hill and are using "B", try applying the accelerator. The engine RPM will -decrease-. Very weird, but correct action.
     
    #12 David Beale, Oct 15, 2009
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  13. M8s

    M8s Retired and Lovin' It

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    Perhaps you know better than me, but I thought that the MG1 spun the engine. That work puts a load on the MG1 and the MG1 burned up the excess electrons that way.
     
    #13 M8s, Oct 15, 2009
  14. fuzzy1

    fuzzy1 Senior Member

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    That may be a semantic difference.

    The ICE is configured for maximum drag as a vacuum pump / air compressor, the combination of both MGs spins it, and the wasted heat energy goes out the ICE exhaust.
     
    #14 fuzzy1, Oct 15, 2009
  15. qbee42

    qbee42 My other car is a boat

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    Exactly what I said. I suppose you explicitly stated that the electric motor uses electricity, but that seems fairly obvious.

    Tom
     
    #15 qbee42, Oct 15, 2009
  16. RDB6lll0

    RDB6lll0 New Member

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    Would a shunt to short out the motor allow it to continue the electrical braking? I think diesel-electric locomotives do this on long descents, but I suppose they have miles of cold steel rails they can use to soak up the resulting heat.
     
    #16 RDB6lll0, Oct 18, 2011
  17. fuzzy1

    fuzzy1 Senior Member

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    ^^ The box of air-cooled shunt resistors on the roof would wreak havoc on Prius's otherwise clean aerodynamics, wasting fuel 98% of the time.
     
    #17 fuzzy1, Oct 19, 2011
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  18. qbee42

    qbee42 My other car is a boat

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    The Prius already does this, but rather than using resistors it spins the ICE as an air pump. The net effect is the same.

    Dynamic brakes on trains use large fans to dissipate the heat, not the rails.

    Tom
     
    #18 qbee42, Oct 19, 2011
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  19. joe2999

    joe2999 New Member

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    Regenerative braking works in mysterious ways, as illustrated by this cartoon.
     

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    #19 joe2999, Nov 4, 2011
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