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HV battery questions: Resting voltages rising???

Discussion in 'Gen 2 Prius Technical Discussion' started by random_username, May 12, 2024.

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  1. random_username

    random_username Junior Member

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    Hello priuschat geniuses,

    I'm currently in the process of trying to recondition two HV batteries. My plan is to start out by combining the good modules to get one of the batteries functional ASAP. But I'm confused by some of the readings I'm getting. (I found one comment with a similar issue in the forums, but no one responded.)

    Pertinent Info:

    - Battery #1 sat in the car for ~6-9 months after failing (I was out of state for 3 months and when I returned, it was dead).

    - I removed it from the car and it sat for another ~2 months while I was working on Battery #2, before I got around to checking the voltages.

    - To my surprise, all the modules on Battery #1 were basically the same (most were 7.60v, with a few +/- 0.01v) except #28 which was 1.42v.

    - I'm in the process of topping off the modules (without discharging) with a hobby charger (EV-Peak CQ3 4x 100w) before doing a load test. (0.3 amps charge with an auto delta peak/7000mAh cutoff.)

    - I noticed today that the modules that have been topped up so far have gone up ~0.03v after resting for a few days, but not the ones that have yet to be topped off. (EDIT: In the first 24hrs they dropped down ~0.20v. Then the next day came up ~0.03v.)

    - I've load tested the ones I've topped off so far and they all drop by the same amount (0.15-0.16v @ 2 min).


    So my questions are...

    1. I understand if you leave the battery in the car, the system will attempt to balance out the modules. So if it came out of the car with 27/28 modules even, then sat for months, does that already confirm that they all have the same delta drop rate?

    2. If the answer to question one is yes, do I really need to load test and recondition the whole pack, or can I just replace #28 with a module with a similar delta drop rate from Battery #2? (time is a factor)

    3. And what's the deal with the resting voltages going up by themselves? Concering my edit: Could it be an issue with the multi-meter I'm using? (AstroAI M6KOR)


    Any insight into these questions -- and to the reconditioning process in general -- is greatly appreciated!
     
    #1 random_username, May 12, 2024
    Last edited: May 12, 2024
  2. PriusCamper

    PriusCamper Senior Member

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    What are you using to put a load on the modules? Seems a bit low for good measurement... You want a 12v 50w bulb or equivalent in a resistor. Aim for .3v loss in two minutes on a newer healthy pack is standard.

    As for the car balancing modules, that is how it's done with lithium in cars equipped with lithium BMS, but for NiMH you have to overcharge a pack a low amp loads (1/3amp) to balance Nickel-Metal Hydride and use a cooling fan because excess charge is dissipated by via heat. The car can't do that NiMH routine, but a high voltage trickle charger with cooling fan can do that, such as products from Maxx Volts or Hybrid Automotive... Or you can build your own: Build Hybrid Battery Maintenance Gear For Under $100 | PriusChat
     
    #2 PriusCamper, May 12, 2024
  3. random_username

    random_username Junior Member

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    Thanks for the quick response!

    I'm using a 12v 55w/65w high beam H4 bulb. I checked the diagram to confirm I have the correct tabs connected. I also noticed the more recently charged modules went down a little slower (0.13-0.14v). Not sure why.

    The charger I'm using is the EV-Peak CQ3 4x 100w and a box fan to keep it cool. It's measuring 14.76-14.86v while charging. Is that enough?

    I thought charging the module at 0.3 amps up to 7000mAh would sufficiently overcharge it. The modules averaged around 8.42v when the charger said they were "full". But there wasn't any noticeable heat coming off them. Is that not the correct process? Perhaps I should turn off the Auto Delta Peak?

    I've read through this thread before, but I admit, some of it is a bit beyond me, so that's why I bought a charger with built in AC power. I've done a fair amount of research over the last year, but this is the first time I'm doing something like this, so apologies if I'm missing something obvious. Thanks.
     
    #3 random_username, May 12, 2024
    Last edited: May 12, 2024
  4. dolj

    dolj Senior Member

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    That is the correct setup for that design. Discharging a little slower is a good thing as it indicates the module(s) is/are in better condition. However, it still must match the capacity of the others that it has to work with. I wouldn't worry about it at this stage until you're ready to assemble the modules.
    Nothing wrong with that setup.
    Yes, that is the correct procedure. The heat is not always perceivable without using a thermometer. At some stage, you will need to turn off the delta peak so you can overcharge long enough to obtain a top balance. 8.4 V sounds about right, too.
    You sound like you're on the right track. Keep up the good work.
     
    #4 dolj, May 13, 2024
  5. random_username

    random_username Junior Member

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    @dolj Thank you for the feedback!
     
    #5 random_username, May 13, 2024
  6. jeff652

    jeff652 Senior Member

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    If you are planning on reconditioning all the modules at once, then you will need something a little bit more substantial than the EV Peak CQ3 charger. To balance the entire pack once it is all put back together again, or to just keep the battery up to date in general, it is much easier to use something like Prolong's setup. Because you have 2 batteries, especially one that is on the worse end, it might not hurt for you to look into reconditioning the entire pack at once.

    Also, discharging the pack down below its normal voltage levels helps recondition the state of the battery as well.

    Just some thoughts,
    Garrett
     
    #6 jeff652, May 13, 2024
  7. mr_guy_mann

    mr_guy_mann Senior Member

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    The battery ecu does not balance the blocks at all. The block to block voltage differences I had after I DIY refurbed my pack were pretty much the same 3 years later.

    There are MANY posts about battery "repair". Some people have done the absolute minimum repair and gotten away with it (for awhile at least). Others have done lots of things and failed immediately.

    I used several hobby chargers and cycled all modules 4-6 times - took almost 5 weeks and it was "fine" for 3+ years and over 50k miles.

    But when that pack had a "glitch", I immediately put in a new Toyota pack.

    Posted via the PriusChat mobile app.
     
    #7 mr_guy_mann, May 13, 2024
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