Hybrid battery gets really low in slick conditions because I'm not braking

Discussion in 'Gen 3 Prius Main Forum' started by ale89515, Jan 23, 2020.

  1. Mendel Leisk

    Mendel Leisk 'Orrible Oracle

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    The battery level indicator is always shown, as far as I know.

    Regarding the optiionals, the Hybrid System Indicator (HSI, and I can never remember the name) is by far my favourite:

    upload_2020-1-29_12-36-26.png

    This one, the Energy Monitor:

    upload_2020-1-29_12-38-2.png

    Is the default display, and a total menace, too distracting. A pretty picture that'll having you driving off the road or into someone.
     
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  2. Maarten28

    Maarten28 Active Member

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    2 bars is 40% SOC, the car will not let it go lower (well, unless in extreme conditions, when it's already at 40% and you start up cold it will go a bit lower), so there is no issue there.
    All bars displayed is 80% and at that point the car will run the ICE to get the charge down.
     
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  3. ChapmanF

    ChapmanF Senior Member

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    I've noticed that my car will very avidly use electric power, when the charge gets up near 80%, to get it down closer to the 60% target, and also use heavy engine braking during deceleration or descent to avoid storing more charge than that.

    I have not, though, ever noticed it just decide while sitting still to burn off excess charge and waste it. That would be a possible thing to do (and it would not really be 'running' the engine, merely using it as a big spinny thing for the electric motor to push around as a way of using up power). That is what is happening during engine braking. I just haven't ever noticed my car wanting to do it while sitting still.
     
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  4. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I've read a few accounts of a few Prius c models doing this. From what I've read, it happens when the battery temperature is high. It would seem that the computer first tries to cool the battery by jacking up the fan speed, and if that doesn't succeed within a minute or so (heat soaked cabin or fan problem) it then tries to dump charge by spinning the engine. The time spent trying to cool down via fan separates the cause and effect by just enough to confuse the driver, to the point that people have started threads to ask about it.

    It hasn't happened in our own car, but we haven't really faced the situation of stopping at the bottom of a hill after parking in the sun all day at the top.
     
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  5. ChapmanF

    ChapmanF Senior Member

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    I'm not sure that running current out of a battery lowers its temperature though.
     
  6. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I don't believe it can or does. I understood the goal to be avoiding the combination of high temperature and high state-of-charge in the name of long term battery health.

    It makes sense to me that the computer would try to drop the temp first- why waste a good charge?
     
  7. fuzzy1

    fuzzy1 Senior Member

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    It depends on the exo- / endo-thermic properties of the battery chemistry, and whether or not resistive heating exceeds endothermic cooling.

    I believe that NiMH batteries can be endothermic during discharge:

    "In a NiCad battery the charging reaction is endothermic, but the discharge reaction is exothermic. So when charging it actually sucks heat from its surroundings and stays cool (until it is full and the reaction finishes), while during discharge it produces heat and gets hotter than you might expect. NiMH batteries do the opposite - they get hot while charging, but cool themselves during discharge."
    batteries - How does charge/discharge current increase battery temperature? - Electrical Engineering Stack Exchange

    Li-ion batteries can be endothermic during a portion of their charge cycle.
     
  8. ChapmanF

    ChapmanF Senior Member

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    I can now call it a night, having learned my new thing for the day. :)
     
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  9. Grit

    Grit Senior Member

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    Similar with dust can compressed air. When you spray dust by holding the nozzle to expel the air, the can will condense on the exterior surface. When you continue to spray the dust with longer durations, frost will form on the surface of the dust can sticking to you fingers and palm.
     
  10. fuzzy1

    fuzzy1 Senior Member

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    That is a completely different mechanism, the Ideal Gas Law, covering the expansion of gases and/or boiling of liquids as pressure drops. It is not from any chemical reaction.

    The rechargeable battery endo-exo-thermic properties are from chemical reactions, not pressure changes.
     
  11. ChapmanF

    ChapmanF Senior Member

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    I think that's also why every time I open the drain valve on my air compressor, it blows out air strongly for a moment, then freezes, and doesn't let more air out until it thaws again.
     
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  12. Grit

    Grit Senior Member

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    Keyword used was “similar”. Not “exactly”
    :)
     
  13. fuzzy1

    fuzzy1 Senior Member

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    That example would be a quite thin example of 'similar'.
     
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