How to determine individual hybrid battery module capacity?

Discussion in 'Gen 2 Prius Technical Discussion' started by app-o-matix, Feb 3, 2021.

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  1. app-o-matix

    app-o-matix Junior Member

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    If my traction battery is out of the car and I have a Prolong charger and discharger, not an RC charger/discharger, is there a way for me to determine the amp hour capacities of my individual cells?
     
    #1 app-o-matix, Feb 3, 2021
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  2. TMR-JWAP

    TMR-JWAP Senior Member

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    There is no easy way.
    If you have an infinite amount of patience, you could document the start time of the discharge, discharge rate of the prolong, and document the 28 individual module voltages every couple minutes and record the time when each module reaches your setpoint (safe to assume 6v at the module is full depletion). Make sure you document any changes in the prolong discharge rate. Using that information you could calculate how many mAh were discharged from each module.

    Then charge it completely and do it again.
     
    #2 TMR-JWAP, Feb 3, 2021
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  3. app-o-matix

    app-o-matix Junior Member

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    Thanks for the response. This is where my brain starts to turn to mush when trying to figure out how to best diagnose my modules. I’ve gone through various posts on various threads on traction battery reconditioning and I often feel like I’m going in a circle. So, if I may ask a series of questions, perhaps, with answers to them, I’ll finally know how best to proceed.

    To preface my questions, my initial situation is as follows:
    • 2007 Prius, 100K miles
    • Had RTOD
    • TorquePro identified at lease one bad module (Block 10)
    • Battery is currently out of the car
    • Possess multimeter, Prolong charger, discharger, and load tester
    • Basic multimeter voltage test identified two bad modules, 8 and 20, with voltages in the 6V range with all others in the 7.86-7.90V range
    • Replaced modules 8 and 20 with modules reading 7.35V
    • Cleaned bus bar terminal plates and nuts
    • Repositioned modules 15-28 into the position previously held by modules 1-14, and vice versa, so that modules previously in or near the center are now at or near the edges, and vice versa
    • Did an initial charge with the Prolong charger for 11 hours - start voltage 222V, max voltage 235V, final stable voltage (4 hours, no change) 233V
    • Turned off charger for the night, turned charger back on this morning - start voltage 224V, current voltage (after 1 hour) 234V
    My questions:
    1. If I admittedly don’t have an infinite amount of patience and, therefore, cannot reasonably (read: cheaply) measure the capacity of each module, am I ultimately missing a vital piece of information that is going to prevent me from truly knowing the quality of the modules I’m using in my pack?
    2. What is the relationship, if any, between load testing, internal resistance, and capacity?
    3. Are internal resistance readings from apps less valuable because they report the IR for a block rather than for individual modules or do additional tests (e.g. simple voltage test, etc.) help me determine a bad module, internal resistance-wise, that is part of a block identified by the app’s IR value?
    4. Even though it doesn’t result in a specific IR value, is load testing (start voltage - 120 sec. load - end voltage) sufficient for determining a module’s IR relative to the other modules?
    5. When load testing a module, after the voltage at 120 seconds is recorded, is there any value in observing what happens, if anything, to the voltage of the module after the load is removed?
    6. If, after load testing, I have identified 28 reasonably healthy modules, should I pair them in blocks by matching modules that had the lowest voltage differences with modules that had greatest voltage differences in load tests?
    7. In what stage of the charging/discharging reconditioning cycle should load testing of individual modules be done? One previous post suggests it should be done last, I’m assuming because the modules will have been conditioned to their fullest. If this is correct, this would mean going through 3-4 days of charging and discharging to find bad modules and, if found, replacing the bad modules followed by another 3-4 day charging/discharging cycle, yes?
    Assistance in finding answers to any of these questions would be greatly appreciated. Thanks!
     
    #3 app-o-matix, Feb 3, 2021
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  4. TMR-JWAP

    TMR-JWAP Senior Member

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    I think we can simplify this quite a bit. The prolong is pretty darn good at improving aged modules, but is useless for trying to fix a failed module. You've already identified and replaced the two obviously bad modules. That's a great start. Now, you should have only 'aged' modules in the pack. Perform the prolong procedures and let that machine do its thing. Put the battery back in the car. There's a couple phone apps available that will let you test the HV battery in the car. Personally, I use an app called Hybrid Assistant/Hybrid Reporter to test batteries (installed in the car) using the AC system. It provides a graph of all 14 blocks so it makes it very easy to see if one block is lagging the others in performance.

    The individual quality of the modules isn't nearly as important as having them fairly well balanced capacity-wise. Your pack will only be as good as the weakest module, and the way the prolong system is designed, it does more 'fixin' to weak modules than to stronger modules, so it improves the balance. This will save you a lot of time and aggravation. I think you'll be fine. Get one of those apps and then you'll be able to keep an eye on the battery. It will be easy to see if any blocks are starting to get weak, allowing you to plan for another prolong cycle, or if it doesn't show improvement, replacing a module.

    This link is for a thread that has several app graphs to give you an idea of what they look like.

    Just Another HV Battery Thread and Experiments | PriusChat
     
    #4 TMR-JWAP, Feb 4, 2021
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  5. HybridCPR

    HybridCPR Junior Member

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    BATTERY OUTPUT: Prius is rated at 28 horsepower OUTPUT of the HV battery, this is 21,000 watts. (efficiency losses likely mean closer to 18-20HP from electric motor) I have observed (Torque Pro) from acceleration testing that at full throttle the pair voltages drop to 12.5-13.2 volts, so about 180 volts output for pack at that load.. That translates to about 120 amps from pack (to get 21KW.). Impedance drop of each pair would supposedly be under 2 VDC, but I see more like 2.5 or 3 VDC.
    Amp=hour ratings are measured at over an 8 hour period, so at about 0.8 amps (Battery industry standard). This changes dramatically at 150 times rated current. LOL. 120 amps is only available for seconds.

    BATTERY CAPACITY DIMINISHMENT: After years, hundreds of thousands of charge/discharge cycles, the amperage capacity diminishes.. I have reconditioned HV batteries that were down to 15-20 % of original, these batteries are not capable of providing acceleration assist. You may notice on the dash meter they go up fast--and down fast. time to replace/recondition.

    TESTING CAPACITY/MATCHING WITH Hybrid Automotive discharger: (Prolong) Buy 14 cheap meters at Harbor freight, monitor pairs. Take a pic of meters each half-hour or hour. When weakness detected, then switch to individual modules. Recondition or replace the fast-failures. Good luck. Len Wallace HybridCPR.
     
    #5 HybridCPR, Feb 4, 2021
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  6. valsor

    valsor Junior Member

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    Most NiMH chargers records miliAmpere-hours charged of discharged. I use readings during discharge as true capacity of the module.
     
    #6 valsor, Mar 22, 2021
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