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Driving Down a Mountain

Discussion in 'Gen 2 Prius Main Forum' started by Aaron, Jul 12, 2011.

  1. Aaron

    Aaron Member

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    Took my 2008 Prius down a huge mountain for the first time yesterday and noticed something strange. While applying the brake my ScanGauge would only read a 83% max charge level even though I was applying the brake well beyond when it reached 83%.

    Also, once I was at max charge for quite awhile (and still pressing on the brake peddle) my Prius started increasing its RPMs on it own and the charge level started to drop. It's like my car didn't like being fully charged and decided on it's own to go back down to 62%. Normal?

    I thought by the time I got down the mountain I would have a fully charged battery, but this was not the case.
     
  2. wjtracy

    wjtracy Senior Member

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    do not know. Wonder if you went down the same steep mountain I did (Rt 40 in PA westbound). What I noticed was after the battery went all-green, there was subtle increased noise. I took this to mean once the battery was charged, some change happens. I probably should have gone to B mode, from reading posts.
     
  3. Aaron

    Aaron Member

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    I was going 55 MPH....too fast for B mode:)
     
  4. wjtracy

    wjtracy Senior Member

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    Me too 55 MPH, but I was thinking you can do 55 in B. My mountain was really steep.
     
  5. seilerts

    seilerts Battery Curmudgeon

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    You cannot "fully" charge the HV battery. The normal SOC range is 40%-80%. The engine RPMs went up because the car was using the HV battery to spin the engine. At this point, all, or almost all braking would have been hydraulic.

    Next time use B.
     
  6. F8L

    F8L Protecting Habitat & AG Lands

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    I wouldn't worry about it. You were not using any extra fuel while the engine rev'd up and your battery was as full as it was going to get. It is weird to experience it though it is by design. It's only happened to me 4 or 5 times. :)
     
  7. Danny Hamilton

    Danny Hamilton Active Member

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    Why do you think 55 MPH is too fast for B mode? I'm pretty sure B mode works all the way up to 110 MPH.
     
  8. Aaron

    Aaron Member

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    How fast can I go in "B"? Could I blow the engine?
     
  9. fuzzy1

    fuzzy1 Senior Member

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    I can speak only for GenIII, but B mode doesn't have a speed limit, at least within the speed range I use. If B mode gives too much braking, then (1) the 'mountain' isn't very steep, and (2) press the gas pedal very lightly to reduce the degree of engine braking, adjusting it to the amount you want.
     
  10. Aaron

    Aaron Member

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    Nice. I was under the impression that if I was going too fast downhill I could damage the engine.
     
  11. fuzzy1

    fuzzy1 Senior Member

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    While I don't like the screaming jet engine howl of the ICE spinning at 4500 RPM in braking mode, it shouldn't be any worse than spinning it that fast while burning fuel to climb the hill.
     
  12. Aaron

    Aaron Member

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    The climb was quite something. Fully loaded with 5 people and gear. 96 F outside. Water temp got to 210 F. The ICE was screaming! But she performed like a champ. It's the hardest I've ran this car. Just turned 60K miles.
     
  13. SpikeVFR

    SpikeVFR New Member

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    Uhhh, why would you say that? I have been in B mode to at least about 75-80 MPH - if the hill is steep enough.
     
  14. Aaron

    Aaron Member

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    Yeah, I just realized B is not the equivalent to Low 1, 2, or 3 on a normal car.
     
  15. Wolfie52

    Wolfie52 Senior "Jr" Member

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    I was using the B mode at 70-75 MPH this weekend. No problem.
     
  16. fuzzy1

    fuzzy1 Senior Member

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    It is approximately equivalent to a downshift in an old technology car when decelerating. When applying power to maintain or increase speed, it doesn't really do anything.
     
  17. qbee42

    qbee42 My other car is a boat

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    Around 140 mph, but only if dropped from a helicopter.

    Tom
     
  18. Aaron

    Aaron Member

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    So THATS the Prius terminal velocity!
     
  19. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    [ame="http://www.youtube.com/watch?v=fIF9ys-hJn0"]‪MGB parachute advertisement‬‏ - YouTube[/ame]

    Darn, I remembered the commercial, but it does not look like the car ever had a chance at terminal velocity. There was a persistent rumor that this was the second drop, the chute did not open the first time. (yes, they needed a second car)

    [​IMG]
     
  20. gialia

    gialia New Member

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    What is the benefit of B mode? I thought that it is only to be used to provide more breaking and not for the whole ride down a mountain.