Module matches pairs??

Discussion in 'Gen 2 Prius Main Forum' started by kenneth winter, Apr 6, 2021.

  1. kenneth winter

    kenneth winter New Member

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    I just spent hours cycle charging my modules and match similar mAmp modules for the reassembly. I only got 67% remaining life and .5 volt difference between best and worst cells.

    If car is comparing best blocks(2 modules) to worst blocks, would it be better to combine best and worst modules in pairs to create the BEST Average cells?? What is the flaw in my logic? I am disappoint with the results of two weeks of work!!
     

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  2. mr_guy_mann

    mr_guy_mann Active Member

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    All the modules are in series, so the capacity of the entire pack is limited to the capacity of the weakest module. If the difference in capacities is too high, then "averaging" isn't going to work. As the weak module is discharging or charging, it will have a higher voltage difference that gets bigger as it reaches the limits of its capacity.

    The "best" way to fix this is to ID the worst modules in the weak blocks by load testing each module. Then put those modules through a couple more discharge and charge cycles to improve capacity.

    On my battery pack I had 4 chargers and it took me about 5 weeks. I did 4 to 6 cycles for each module- depending on what the capacity was. Most got 1.5A disharge to 6.0V then 7200mAh charge at 2A (delta V disabled). Some needed more cycles going down to 5. 0V or lower with 7500mAh to 8000mAh charge.

    Ended up with measured capacity ranging from 5600 to 6200 mAh - I "averaged" those into blocks and have 90% capacity with a 0.15 to 0.27V difference. Others have had different methods that worked for them.

    Posted via the PriusChat mobile app.
     
  3. PriusCamper

    PriusCamper Senior Member

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    Load testing done? As in voltage loss of 2min at 50W will help you find the bad modules.
     
  4. kenneth winter

    kenneth winter New Member

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    Can you state the process you used to test for capc
    I did load testing with the RC hobby charger... BUT It ONLY pulls 2 AMPs.. It takes hours to run the discharge cycle.. All batteries (4 replaced) showed 6000-6400 Ma on the RC discharge cycle at 2 amps starting at 8.4 volts...

    I am thinking the slow (2 amp) discharge is NOT a representative load scenario??
    I am ponder using a 100 AMP car battery charger??
     
  5. PriusCamper

    PriusCamper Senior Member

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    Yeah, you need more amps for a load test, but not 100amps unless you're testing whole pack. Easiest way is to grab your headlight bulb if it's a normal hallogen 50w 12v bulb, or buy one if you have LED or LID.

    As for using the chargers to track amount of ma going into pack, that might be slightly accurate with cheap chargers if you're working with Lithium, but with NiMH, depending on conditions, as much as 30% of that ma sent to modules will be lost as heat and charging the battery from total discharge is not easy, nor safe. Best to keep modules cool and charge them in stages.

    One technique that I prefer is discharging multiple modules with multiple multi-tester and light bulbs and watch them race each other... Keep the ones that last the longest and ditch the ones that discharge fastest after you've done three rounds of discharging/reconditioning.
     
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