Hybrid battery balancing

Discussion in 'Gen 2 Prius Technical Discussion' started by Jonscheets, Sep 26, 2017.

  1. vjekobalas

    vjekobalas Junior Member

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    I'm not sure if I made myself clear - the battery is removed from the car,
    sitting on a table in one piece as it came from the car with all wiring
    disconnected/ modules are disconnected from one another and I am doing
    a module by module reconditioning not a pack level reconditioning/balancing.

    I am using the CQ3 charger with slightly reduced settings (post #117) to what TMR-JWAP had
    in post #76 of this thread.The modules (info from the Toyota technician) are the same
    as the Prius C and there are 20 modules in the pack.

    I am writing because it was my first charging and I had a bit of a panic attack during the
    charging phase when I saw what I then thought of as being high battery voltages and that
    the charging was not stopping via delta V test - I thought the voltage would rise to a level
    at which the modules would be damaged so I stopped the charging at 4400mAh
    on all modules.

    From dolj's post I presume the voltages are normal which has given me confidence
    that I may be doing the right thing and that the modules may be OK but I would appreciate
    if someone experienced could confirm whether I should continue with my "more conservative settings"
    or use TMR-JWAP's and whether I should add a an automatic capacity rule lower than 6000mAh
    - I want to avoid stressing the modules and ending up with garbage at the end.
     
    #121 vjekobalas, Sep 22, 2021
    Last edited: Sep 22, 2021
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  2. vvillovv

    vvillovv Senior Member

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    lower amp charging is universally considered safer. The thing is that even the very low amp charge cycling, is that there is still no guaranty you will not have garbage results from bad modules even with the lower slower cycling.
    If I read correctly TMR-JWAP posted that he sets Delta V to default because the Delta V cutoff doesn't appear to work as it should for him.

    If the cycling doesn't help the weaker module, you have to be prepared to locate replacements.
     
  3. mr_guy_mann

    mr_guy_mann Active Member

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    Well, AFAIK the whole point of cycling the modules is to "gently" stress them in order to recover capacity. Discharging and charging within "normal" limits seems to accomplish very little. The general consensus is that if a few cycles do not show decent capacity during the discharge phase, then you go to a lower voltage on the discharge and higher mAh on the charge. I can't find my notes from my refurb, but some modules needed 5-6 cycles - some I had to go down to 5V and charged 7500 mAh (no delta V)- with a fan pushing air through the bottom duct continuously. I replaced 5 or 6 modules total- seems to be doing decently over 1 year and 15,000+miles later.
     
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  4. vjekobalas

    vjekobalas Junior Member

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    I fully appreciate and agree with the need to "gently" stress the modules and

    the methods to cycle to wake up the modules to see whether they can be revived but there's a few points
    which are not clear to me after actually doing the first cycle :

    Let's start with the charge cycle as that is where I have most concern now:
    Does everyone allow the charger to go to voltages of the order I have seen (8.49V - 8.67V) (dolj confirmed
    that they were normal - would like to hear what others have to say).

    From TMR-JWAP's post above which looks like I didn't read closely enough/ associate closely enough to the charge/discharge
    curve (attached) it may be that at the voltages I was seeing, I was just pumping charge into heat and I
    should have stopped the charge at or below eg. 6*1.4V = 8.4V . I would have expected the charger to stop the charging
    via the Delta V test before these voltages but the charger stuck to the voltage and kept pumping.
    I am also now wondering whether my choice of 15mV for Delta V (from reading it should be 3mV-5mV/cell),
    instead of making the test more sensitive than TMR-JWAP's 20mV - maybe the charger is not seeing the jump
    in voltage and thinks it should continue charging. I am especially concerned about this because I am reading
    how everyone is not able to reach charging capacity but in my case, the charger is just pumping away.

    I don't have any temperature sensors and would really like to know how TMR-JWAP senses the "heat generation"
    i.e. what type of sensor/where they are placed to get early heat detection as the modules are cooled
    with air and I suppose it is difficult to measure unless it is very sensitive.

    For the discharge cycle, I would like to know if my idea of going down to 6.6V instead of 6.0V makes sense
    (at least for one cycle) to ensure most unbalanced cells are not reverse charged.
     

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    #124 vjekobalas, Sep 23, 2021
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  5. vvillovv

    vvillovv Senior Member

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    chances are the weak module you are worrying about is already at it life expectancy, but you can't tell from 1 cycle without tons of experience from cycling other modules. Second and third cycles will typically tell more, and 4th and 5th cycles should show the most a module has left to offer.
    Weaker modules will charge to higher voltages. as well as show other signs of degradation before and during discharge. Before the discharge cycle they typically loose charge quicker than the stronger modules (self discharge) and during the discharge cycle (the discharge slope is much steeper) than the slope of stronger cells.
    Without knowing how TMR-JWAP gets his modules temperatures, (I'd also be interested to know ;)) you can use and infered thermometer, remove the fan for a minute at take a few reading to see if the temps increase in the module. or just use you hand to see if the module is getting hotter.

    Finally, limiting the discharge cutoff to 6.6 volts for the first cycle is OK. some might not agree but in my mind it's just nit picking about how another person chooses to get there discharge data. Further,

    there is a process called deep discharge where the operator reduces the discharge voltage on successive cycles. Again, some have positive results and some others don't.
     
  6. vjekobalas

    vjekobalas Junior Member

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    Sorry if I'm beating a dead horse asking all sorts of questions but it beats me making a lot of mistakes.
    You didn't say anything about the voltages I quoted (8.49V to 8.67V) so I assume you also consider these voltages
    to be OK for the charging cycle.
    What do you consider as normal voltages for a newer module and "higher voltages"
    of older cells ?
    Does the charging cycle end for you via Delta V check from the charger or seem not to end
    (voltage not changing or sometimes stepping down slightly and then back up) with charge continuing / should I
    just be using a lower capacity cutoff ?
    It is sounding to me like I'm the only one the charge cycle seems to be continuing or am I coming to the
    wrong conclusion i.e. it will eventually drop voltage and Delta V check stop the charge ?

    Thanks, that gives me confidence that my logic makes sense.

    Hope others can chime in and give their view.
     
  7. vvillovv

    vvillovv Senior Member

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    Yes,
    Now I get what Dolj was referring to when mentioning the 20% to 80% SOC and .34 amp float charge. As well as your concerns about continuing the 1.6 amp charge above that voltage level in the modules.

    A lot more than I could have imagined from reading some of the three threads I've seen your posts in about the yaris.

    :)
     
  8. TMR-JWAP

    TMR-JWAP Senior Member

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    The final discharge and charge voltage is going to vary depending on the current setpoint you're using, the wire gauge you're using, and the internal resistance of the module. There's no perfect answer.

    In my case, with my settings, if I have a final charge voltage that's over 9.0, I consider it a trigger for further evaluation/examining.
    Let's assume all 28 modules being cycled are in the same range of 9-9.1 volts. Is that a problem? Not necessarily. Do they all test with similar capacity? Are any swelling? Are they all holding the charge?

    If I have 28 modules and 26 finish at 8.69 volts and 2 of them finish at >9 volts, then it's more likely those modules have some issues. It's also likely those modules may show some swelling compared to the others. When in doubt, throw it out. There's no need to build a battery that has a marginal module. Why go through all the work and then slap it together with a questionable module?

    Temperatures are easy. My test rig is the case bottom from a Gen 2 with an OEM duct and OEM fan blowing air into it. When I attach an assembly of 28 compressed modules on the case, I also attach the bottom plastic flow blocker, which creates an air supply plenum under the modules. Cooling air is now forced upward between all 28 modules. It's basically just like OEM but in the opposite direction.

    If I have any concerns about a module I can monitor it's temperature either using my fluke temperature gun or extech Type K thermocouple reader. Every module has a 'well' in the top that works pretty well for inserting a thermocouple tip. You can even pack the 'well' with bits of paper towel to seal the tip in it. It's pretty rare I worry about temperature because there's plenty of other indications of a module being bad.

    Every time I rig up a new set of 28 modules, I ALWAYS perform the discharge first so I know which modules are likely to be problems.
    During the charge cycle, I can run my hand across the top of the battery and feel the air flow. It's easy to feel warm air or not warm air. If it's only halfway through the charge cycle and the air is extremely warm.
     
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  9. vjekobalas

    vjekobalas Junior Member

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    Hat off to you/thank you very much TMR-JWAP !!!- I now feel confident to continue and hopefuly
    I don't ruin my daughter's battery :)
     
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  10. C Wagner

    C Wagner Member

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    If you haven't already taken a look at the Wiki on HV battery repair I started, take a look. It references lots of other videos and work by earlier/better folks but will be hopefully useful in adding large amount of info you'll need to know to do this project. I think it's in my signature/footer right below all my posts...
     
  11. C Wagner

    C Wagner Member

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    In addition to mentioning "read up as much as possible", as I just did in my earlier reply to you, if I were doing it again, I'd put little water/party balloons over all the vent valves in the modules. Yes, you want to be working on them individually in your garage, basement etc. No you don't want NiMH venting to your space!
     
  12. C Wagner

    C Wagner Member

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    Yes, you really want a fan pushing air on your precious modules. I took the ducting from the car and taped it up to the modules kept bolted into their battery case's rods/cage. I connected a blower (really just a large 12v computer fan to a 12v power source (heck, I bet you have one!) and that blew air through the ducting and over the modules (just like in the car!) all the time they were charging...
     
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