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Working on traction battery

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Kats_Pajamaz, Jul 16, 2023.

  1. Kats_Pajamaz

    Kats_Pajamaz Junior Member

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    Due to a lack of knowledge while trying to fix my prius, I ran my traction battery too low to attempt to start the car. So I went through the process of charging my modules individually, then balancing them afterward, all while they were in the rack. They've had ample time to cool with a fan blowing on them, but they dont sit down perfectly into the rack. None of the modules are noticeably swollen, so I assume it is just a tiny bit of expansion on a bunch of the modules. I have the bolts in the rack, they just aren't fully tightened down to the plastic edge piece. Maybe about 1/3-1/2 inserted.

    My question is, am I able to just tighten it down and allow the compression of that to happen? I don't want to just assume that since they are batteries and I would rather them not rupture.

    Additional question, is it necessary for the bolts to be fully tightened, or is it normal to leave them out a bit when dealing with these kinds of modules once they start to age?
     
  2. TMR-JWAP

    TMR-JWAP Senior Member

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    I'm confused. If you charged them while they were in the rack, why are the bolts loose?
    It sounds more to me like you charged them while they were NOT "under compression" and they've swollen a bit. If the bolts still have an inch before they're fully seated, I'd let the modules sit for a day or so, so they "unswell" a bit before fully tightening those clamp bolts. Hopefully no permanent damage was done to the modules.

    Yes, the clamp bolts need to be fully seated. The modules need to be spaced correctly to allow the underside mounting fasteners to fit correctly.
     
  3. Tombukt2

    Tombukt2 Senior Member

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    You're supposed to charge them racked up squeezed by those rods and end plates. So what happened here You let the bolts loose started charging the battery modules and they started to swell individually as you're going down in one by one why didn't you leave the rack tightened? I'm not really understanding what went on here but yeah the modules will swell You want to do all this stuff while they're squeezed and racked. Once you unrack them if you working on them individually you better be careful not to overcharge overheat whatever then you're not going to be a happy camper like now I guess.
     
  4. Kats_Pajamaz

    Kats_Pajamaz Junior Member

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    Ok so to clarify, while charging, they were fully tightened in the rack. I hadn't loosened anything at that point. I removed them so that I could arrange them so all the positive and negative terminals were aligned so that I could perform the balancing. Before actually performing the balancing, I went to retighten them into the rack, but at that point the rack wouldnt close all the way. So to avoid confusion, I literally loosened the rack, turned half of the modules around, and immediately went to resecure the rack, but it wouldnt fit all the way. I let it sit for 2 days to allow it to close more, at which point, it hadnt really gone down much, sitting at the same point I described. I went ahead with the passive balancing process (connecting all the positive terminals together and all the negative terminals together to allow the voltage to equalize. I figured that since that shouldnt be putting much strain on the modules, having it not fully tightened probably wouldnt matter. I still had a fan blowing on it during this process.

    I had assumed that maybe they werent fitting all the way because they werent in their original positions, and had assumed it would fit properly once I flipped them back around to put them to original. The balancing process, with the rack not fully compressed has not caused them to expand any more than they were, because the rack still fits to the same position.

    As of now, the only thing I can think to do is let it sit longer and see if it goes down, or to slowly tighten to the bolts down over several hours. I closely inspected the modules and there are no obvious signs of swelling on any individual modules.
     
  5. PriusCamper

    PriusCamper Senior Member

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    That dude on youtube who shows people how to do passive balancing is wrong... That's how you balance Lithium at the bottom of its power curve, whereas NiMH is balanced at the top at max charge via a high voltage trickle charger and the fan to keep that overcharge from heating up the modules, which is the product Maxx Volts and Prolong sell, or you can build your own for $100: Build Hybrid Battery Maintenance Gear For Under $100 | PriusChat

    What's confusing about what your saying is the metal rack has some ears on the ends that help hold the pack in place while you fully tighten the bolts. You're just gonna have to keep trying to tighten those bolts until it's compressed enough for those ears to be back in place... And in general any kind of warping or expanding of modules will return back to its flat shape under the pressure of the rack after a few cycles of heating and cooling under normal use.

    More to the point, you're saying that there's no expansion on the sides of the modules, but the fact bolts aren't all the way tight indicates there is. And if a module inflates too much you won't be able to get it compressed again.
     
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  6. Kats_Pajamaz

    Kats_Pajamaz Junior Member

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    Well I've watched several videos on balancing and they all say to balance it once they are charged up, which is what I did. Whether that is right or not, I can't say for sure. I don't really know what you mean by ears that hold it in place so I can tighten it down, but I have all 4 bolts in, and I can definitely tighten it down, I just wasn't sure if that was a smart idea to have to use force to close them back up, or if they were supposed to fit easily. And if you read more closely, I said there is no obvious bulging of any individual modules, so it must be a small amount throughout many of them.
     
  7. Mendel Leisk

    Mendel Leisk Luddite

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    Make a compression jig? Something along these lines:

    Get four threaded rod with nuts and washers. Place timber blocking vertically at the ends of the cell stack, with holes for the threaded rod top and bottom. Assemble all and sequentially tighten the nuts till the stack compresses enough to suit the regular rod length.

    IMG_1632.jpeg
    A third such assembly at the middle might help?
     
  8. rjparker

    rjparker Tu Humilde Sirviente

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    I think a compression jig on expanded modules is asking for trouble. Ruptures or worse.
     
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  9. ChapmanF

    ChapmanF Senior Member

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    Yeah, I don't know how promising it sounds to resquish expanded modules. Too bad. Worth a try, perhaps, but I might be even more worried about invisible damage than about the visible kind.

    My old Gen 1 repair manual took pains to say never to loosen the compression bolts before four hours had passed since electrical activity in the battery, presumably to let the modules settle down so they wouldn't swell as the tension came off. I haven't checked the later repair manuals to see what they say in the same instructions, but I assume there is some similar note.

    It seems like the kind of note that might not always make it into youtube videos or other internet-alternative versions of repair instructions. Details like that are what make me so often recommend going straight to the repair manual and carefully studying the steps there.

    Toyota Service Information and Where To Find It | PriusChat
     
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  10. PriusCamper

    PriusCamper Senior Member

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    I run into this installing Nexcell packs... I can't use the compression rack if the old battery is still warm. Now that I have a spare rack it's not an issue. But I'm glad I sensed the expansion pressure ready to bust out before they were able to bust out the first time. It was a close call...

    Just found this article: Top 3 Reasons Brake Dust Shields are Necessary | YourMechanic Advice
     
    #10 PriusCamper, Jul 16, 2023
    Last edited: Jul 16, 2023
  11. Kats_Pajamaz

    Kats_Pajamaz Junior Member

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    Thanks for the help guys. I ended up just letting them cool more, while trying to lightly tighten it down a bit at a time, and each time I went to tighten it down more, the bolts felt a bit loose, so I guess i really did just need it to cool more, which seems odd, but I got them all in the pack.
     
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