HV Battery- Cell Bulge Issues

Discussion in 'Gen 2 Prius Technical Discussion' started by srysoldout, Aug 29, 2021.

  1. srysoldout

    srysoldout New Member

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    Hi all, I’ve been on this site for some time now without seeing too many results for discussion of the nimh cell bulging when charging a module under high current.

    I recently had my hybrid battery go out after a drive over the pass, throwing the red triangle but surprisingly no battery codes. I gave it a look and turns out 80% of the modules were bad, which means that the previous owner left the car in bad shape (I’ve owned the car for three months). I followed a YouTube guide without consulting the allmighty Prius Chat, and got as far as replacing the bad modules with replacement ones from Ebay, but charging them OUTSIDE of the battery casing. I didn’t think to remove the old batteries after load testing, nor did I see any swelling or bulging during the balancing process.

    Multicharger settings:

    C: 5.0A auto charge
    -7500MaH limit
    -6.0V cutoff

    D: 1.0A
    -7500MaH limit
    -6.0V cutoff

    none of the modules got close to 6500MaH, which was expected for used batteries. Anyway, after completely charging the new replacement modules I began to notice some outward bulging when reaching high charge thresholds. Same with discharging. Lots of heat was generated after the cell reached capacity, resulting in the swelling. Unfortunately, I got through all of them and began mounting them back on before failing to fit them into the casing (gee, who would’ve known). So after the fact, is there a way to compress the modules together when discharging so that they will fit inside the casing? Should I let them self-discharge over weeks on their own, or should I clamp them down while doing another discharge? Just really disappointed in myself for lacking common sense here, even on my first time. I’ve attached some pictures of the issue down below, of what it should look like vs the mess I’ve gotten into with the modular separation.
     

    Attached Files:

  2. edthefox5

    edthefox5 Senior Member

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    I'm no battery expert have installed my own 2K toaster pack but one thing I do know and that's never high current charge these battery modules unbolted. The modules will quickly distend. And if distended are ruined. Those are ruined.

    The pack as a whole must be bolted up tight together as they normally sit in the battery box. Then a fan or fans must be focused on them to dissipate heat.

    Prolong chargers for instance use a charge of approx 350 milliamps to prevent this very issue. Low heat so about 20+ hours to balance the whole pack so never an over heat. I used that for about 3 years with no issue.

    use the search forums link up top and search

    hybrid battery

    hundreds of posts all of this is discussed in depth along with horrible pictures of this exact scenario.
     
  3. JohnPrius3005

    JohnPrius3005 Junior Member

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    Sorry to hear about your bulged modules. I'm definitely no expert, but if I was in your shoes I would do this:
    Visit a few junkyards or local places which sell used Prius parts. With some persistence due to the fact there are so many Priusses out there you'll probably be able to find a suitable, low mileage battery from a wreck. Or better still a battery from a much newer Prius wreck from which you can salvage the modules and replace yours.
    If you get the "newer" battery, just replace your modules. If you get a full compatible battery, just replace your entire battery as a unit.
    If you get the full compatible battery, I would take your swollen modules and wait a few weeks to see if the swelling goes down. (Or discharge the modules individually, slowly). If it does, I would install the modules back in the old battery and build a "grid charger" - it costs less than $100 - and then charge the battery as a unit. See what the voltage tops out at. Wait a few weeks, or discharge the battery with a low suitable load, and repeat. It's possible you'll find your once swollen modules are fine. If not, you'll have a grid charger for future use and new knowledge.
     
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  4. SFO

    SFO Senior Member

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    Welcome to PriuusChat!!

    The "advanced search" feature can really help when researching or getting up to speed : Search | PriusChat

    As mentioned above, you might find this DIY "grid charger" thread of interest : DIY Grid Reconditioning Charger | PriusChat

    FYI : your posts are being moderated until you've posted 5 times.
     
    JohnPrius3005 likes this.
  5. james nancy

    james nancy Junior Member

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    When the battery is fully charged, hydrogen gas is produced, and when the voltage is lower than the cut-off voltage and still discharged, oxygen gas is produced. Therefore, it is normal to expand after being fully charged. Because the exhaust valve can be opened at about 80dpi, the plastic casing is not enough to withstand such pressure, so Toyota designed the splint. Fasten the battery. When my charge is complete, it will also heat up and expand. I think that as long as the deformation is not very serious and the temperature is not very high, it is enough to reduce the current when it is almost fully charged.
    After the battery is swollen, you can wait a while or discharge it to recover. Before installation, I usually discharge the voltage to 6.95v, which is 6.95v with load. All modules are the same on 6.95. At this time, there is neither overcharge nor overdischarge. Probably the battery ecu is also based on this voltage to determine when to stop discharging and start charging, which is better than the fully charged state. It also feels better than the 7.2-8.0v installation. This is a low-voltage installation, and the battery will be charged when the engine is running.
     
    #5 james nancy, Sep 9, 2021
    Last edited: Sep 9, 2021
  6. srysoldout

    srysoldout New Member

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    Thank you all for the replies! Advice taken into consideration.
     
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