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Replacing battery modules, need to rebalance pack?

Discussion in 'Gen 3 Prius Main Forum' started by PeterPrius2007, Dec 21, 2022.

  1. PeterPrius2007

    PeterPrius2007 Junior Member

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    I'm getting 4 used modules from a shop here. They have gone through 5 or so charge/discharge cycles to ensure capacity is sufficient.
    Do I have to re-balance the whole HV pack after replace the bad modules with these?
     
    #1 PeterPrius2007, Dec 21, 2022
  2. bisco

    bisco cookie crumbler

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    it will extend the length of time to the next p0a80, but isn't absolutely necessary. it is helpful if the voltages are close to the old ones
     
    #2 bisco, Dec 21, 2022
  3. JC91006

    JC91006 Senior Member

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    If you are needing to replace 4 modules in your pack, it's best you rebalance the entire pack. It can't be in good shape if you are needing to replace 4 of them
     
    #3 JC91006, Dec 21, 2022
  4. PeterPrius2007

    PeterPrius2007 Junior Member

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    One module is really bad. Then another is not looking great, and then the other two I wanted to replace just because I'd be opening the pack anyways and they are the next two in rank with lowest voltage. So I could probably get away with replacing 1 or 2 but I figure may as well replace those that look like they might fail next sometime down the road.

    I basically ranked each module in how often they had the lowest voltage / great bias from average, using OBD data in different driving scenarios.

     
    #4 PeterPrius2007, Dec 21, 2022
  5. JC91006

    JC91006 Senior Member

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    Well without better equipment, you'll never find the stronger/weaker modules with this method. You're better off doing a timed load test on each module for 120 seconds using a headlight bulb.
     
    #5 JC91006, Dec 21, 2022
  6. PeterPrius2007

    PeterPrius2007 Junior Member

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    I caught a P0A80 failure on ODB. It shows the voltage separation pretty clear and I can see the voltage dropout of the worst modules in the attached graph. The group of solid lines are the individual module voltages (deep red is the average). In the data, I count how often a certain module has the lowest voltage, and I believe this is a good determination of the worst performing modules. But in this case, it seems very clear that V8 is completely in failure, and three more are well below average.

     

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    #6 PeterPrius2007, Dec 22, 2022
    Last edited: Dec 22, 2022
  7. Grit

    Grit Senior Member

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    How many quarters do you have?
     
    #7 Grit, Dec 23, 2022
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    After reading the entire current thread, I think you're on the right track. A couple things to keep in mind.

    They have gone through 5 or so charge/discharge cycles to ensure capacity is sufficient. This doesn't mean squat unless you have capacity numbers. I can cycle a POS module 5 times or 500 times, and it will still be a POS. You need to get more info from that shop as to the tested capacity value of each module. At least that way you can compare it to a new module(6500 rated, but varies based on testing method), and to your current modules if you have those numbers. Do a search for "Lebron James theory".

    Do I have to re-balance the whole HV pack after replace the bad modules with these? If your modules are good, and you're confident you're replacing the failed module plus the 4 next weakest modules, and these replacement modules are not super good or super bad,you're very likely going to be just fine without further balancing.
     
    #8 TMR-JWAP, Dec 23, 2022
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