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NiMH battery charging behavior

Discussion in 'Gen 3 Prius Technical Discussion' started by Lasllc, Sep 3, 2015.

  1. Lasllc

    Lasllc New Member

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    I did not want to hijack the previous battery cycling thread . . .but

    I am quite familiar with NiMH batteries, but on a much smaller scale; 20-30 volts, 35-130 amp out. On these batteries it will take 10 to 20 cycles to approximately 80% depletion before the battery reaches its maximum charge potential (assuming proper charging and cell balancing regimens are followed).
    With our limited experience in our new Prius, it seems the battery sort of cycles in the middle third of its total potential. So it would seem (from my experience with this chemistry) that an external, manual cycling may be beneficial. On the other hand I am certain that the charge - balancing circuitry is programed to take this in hand. The chemistry can not be too different. Am I off track here ?
     
    #1 Lasllc, Sep 3, 2015
  2. bisco

    bisco cookie crumbler

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    i think you're spot on, toyota has taken care of all of this for us.
     
    #2 bisco, Sep 3, 2015
  3. mrbigh

    mrbigh Prius Absolutum Dominium

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    I drove a Prius II generation for 5 years and never had to touch the HV battery at all. As part of my background, I had made the first PHEV conversion in 2006 in the North Eastern region of the USA, lasting until today in another Prius hatchback.
    I never had a drop-out of any cell in the OEM pack, neider lost performance of the hole assembly.
    Your initial worries about cell balancing will be minimized once you start utilize your vehicle and see that nothing bad will happen to the hybrid system battery. It is a pretty reliable and simple engineering equipment.
     
    #3 mrbigh, Sep 4, 2015
  4. macman408

    macman408 Electron Guidance Counselor

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    Also, to extend longevity, the Prius battery is used in a fairly narrow discharge range; about 40% to 80% SoC at most (i.e. a range of 40%). But most charge/discharge cycles will only be a couple percent, from braking as you stop and then accelerating back up to speed. Using only a small depth of discharge greatly increases the number of cycles that you get from the battery before it fails; roughly exponentially, if I recall correctly. So they're very purposefully not doing any deep discharges to help make sure that the battery lasts for many years.
     
    #4 macman408, Sep 5, 2015
  5. jeff652

    jeff652 Senior Member

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    Prius battery packs have a finite life cycle, just like all NiMh batteries:

    [​IMG]

    Reduced capacity due to crystal formation within the cells and voltage imbalance is extremely common. The vehicle cannot correct the memory effect and imbalance problems on its own. When used as preventative maintenance, our Prolong™ Battery Systems will break down the memory effect and restore cell balance. We have scores of fleet & private party 2010-2015 Prius owners using our systems to prevent battery decay from occurring.

    Here is a before & after example of using our systems on a 2009 Camry Hybrid. The car had ~130k miles and no codes of any kind. Our systems increased the usable battery capacity by 12%:
    [​IMG]
     

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    #5 jeff652, Sep 18, 2015
    rogerdpack likes this.
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