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Over Charging Full Hybird Battery For A Long Time?

Discussion in 'Gen 2 Prius Technical Discussion' started by ebikeman, Dec 19, 2023.

  1. ebikeman

    ebikeman Junior Member

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    I have followed rechargeable battery technology since the 1970's. With the battery's of today, one of the worst things you can do is leave a battery fully charged. Cells degrade faster. I can see when I drive under normal circumstances, Toyota designed a little bit of uncharged at the top of the battery.

    Probable the worst thing you can do to wreck a rechargeable battery is keep charging it after it's full. "Wreck" is probable an understatement. They can blow up or catch fire. If you search the news, all over the country people's homes have been destroyed by ebike fires. Local R/C hobie store burnt down because the kid left his battery charged over the weekend.

    So here's my question;

    I drive up a mountain pass, lets say battery is 50% on the screen. As I come down the mountain, I see the battery is charging. After about 2 minutes, the battery shows green, full.

    As I go down the mountain another hour, the whole time the screen shows the battery getting charged after it's full.

    Going down the mountain in my other car, I take it out of OD and into 3rd to help slow the car. If I put the Prius in "B" to help hold me back, it puts more current in the full battery. It never stops showing the arrows sending current into the full battery.

    I'm wondering if the screen is a "basic representation" of what's happening, or, if that screen is absolute?

    Seems Toyota has this system pretty figured out. Can't imagine them designing a system that charges a full charged battery for as long as you go down hill

    Does anyone know if the screen is a "general guide" or absolutely specific to what the car is doing?

    Thank you,
    ebm
     
    #1 ebikeman, Dec 19, 2023
  2. Tombukt2

    Tombukt2 Senior Member

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    To me that display just shows that everything is working as designed everything is flowing as it should by the flowchart with no voltages resistances or any of that implied at all.
     
    #2 Tombukt2, Dec 19, 2023
  3. PriusCamper

    PriusCamper Senior Member

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    The battery computer does a great job at protecting your pack from overcharging on long downhills as long as you haven't wiped out the SOC in memory by disconnecting the 12v battery.

    Also, NiMH cells are actually balanced by overcharging at a supper low 1/3rd of an amp and you are correct that overcharging at amps higher than that will quickly destroy cells.

    And with Lithium, which is balanced at the bottom of the charge, even minor low amp overcharging will destroy cells.
     
    #3 PriusCamper, Dec 19, 2023
  4. bisco

    bisco cookie crumbler

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    when the software detects a full battery, it stops charging and spins the engine to burn off excess regeneration
     
    #4 bisco, Dec 19, 2023
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  5. royrose

    royrose Senior Member

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    Yes and when the display shows a full battery it is actually at around 80%, not allowed to go over that.
     
    #5 royrose, Dec 19, 2023
  6. PriusCamper

    PriusCamper Senior Member

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    While it's not allowed to go over that 80% charge level there all kinds of ways that sometimes it does. Like metal on metal brakes, or if you disconnect your 12v for a few minutes when at the 80% charge level. Or if you charge and balance your hybrid pack without the battery computer finding out about it because car wasn't turned on.

    Fortunately, NiMH handles too much charge better than most other battery chemistries, as long as it doesn't overheat...
     
    #6 PriusCamper, Dec 19, 2023
  7. ebikeman

    ebikeman Junior Member

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    Thank you for the reply's.

    I did disconnect the 12V battery last week to put new front brake pads. They where about as thin as could be without metal to metal.

    Now I'm scared, What does "as long as you haven't wiped out the SOC in memory by disconnecting the 12v battery" mean?

    Thank you,
    ebm
     
    #7 ebikeman, Dec 26, 2023
  8. dolj

    dolj Senior Member

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    If your battery was not at 80% charge (that is eight green bars) on the Energy Monitor screen when you disconnected the 12 V battery, I wouldn't worry about it. The ECU will have reset to a default of 60% SoC until it recalculates the true SoC in a relatively short while.

    I'm not sure even I know to what is being alluded in that post.
     
    #8 dolj, Dec 27, 2023
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