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Module balancing sanity check

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by wnrsm, May 5, 2019.

  1. wnrsm

    wnrsm Junior Member

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    Thank you all for the (very very long) threads about battery balancing. I'm posting her because my experience is turning out a bit different/weird.

    2005 Prius, 110k miles, driven in Washington DC area - on the hot side of things, but not the hot hot south.

    The car sat for a week or two. I got the error on the dash, the Dr. Prius app showed one module with relatively lower voltage and another one with slighty lower voltage. ICE is running often. Battery SOC swinging quickly between full and empty. I pulled the HV battery and started balance charging with this charger. (Quad 100W charger)

    Initial voltage readings and a 60-second load test identified four modules that were likely failing. Balance charging results confirmed that I have 24 consistent modules and those four in relatively bad shape.

    I'm doing the D->C cycling. Charge timer off. 7400mAh charge cutoff. Tried 1.5A to 3A charging rates. Discharging at the charger's configured maximum of 5A (the readout shows much less though) until module voltage drops to 6V. Typically the charger reaches the 7400mAh cutoff. I tried a 8200mAh value once with the same results. The charger stops after one cycle and I restart it.

    Now for the results. 24 modules are showing discharge down to 6V with 6300-6500mAh. I am having a difficult time believing that these modules have this much capacity performance at 14 years old. I trust the results to identify consistently-behaving modules and the four bad ones, but how do I find replacement battery modules that match the current health of the 24 survivors?

    I bought four modules from ebay among two sellers. I clamped and balance charged with the same parameters so that I could compare them to the 24 survivors. They showed 1800mAh-3300mAh discharge output to 6V. I'm replacing the four modules because they're showing poorly in resting voltage drop and the voltage-drop load tes. Those four modules are 1468mAh, 3283mAh, 5268mAh, and 5697mAh

    These replacement modules do not match my pack's survivors and are of similar or inferior performance as the modules I'm replacing.

    Am I doing anything wrong here? How do I find four modules that perform similarly to my 14 year old pack? Would reporting/requesting 6200mAh modules seem obnoxious or reasonable?

    Thanks!
     
  2. SFO

    SFO Senior Member

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    Lets call in a couple of heavy hitters (there are others) for your replacement module needs : @TMR-JWAP and @ericbecky
     
  3. landspeed

    landspeed Active Member

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    In your battery : did you look at the battery computer (which is stored in the battery although in the 'area' off to one side). It has an orange connector plug. If you unplug the computer, do the plug and computer look clean, or is there corrosion?

    Assuming you have not had a failure (plasma short circuit) that usually occurs inside the battery computer and melts a lot of things, and leaves metal vapour deposits everywhere, then the other option is bad battery modules / cells. This usually means replacement unless you want to experiment with adding more fluid and electrolyte to the cells, which some people have had miraculous success with, although I have never done it and it seems to be 'bleeding edge / experimental' stuff at this time...
     
  4. landspeed

    landspeed Active Member

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    PS I would report eBay sellers selling dead modules as 'good' if you are sure they are 'dead'...
     
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  5. TMR-JWAP

    TMR-JWAP Senior Member

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    Using the link you provided for the charger, select the tab that lets you look at the owner's manual. It specifies that the charger is capable of 100W in charge mode and 10W in discharge mode. This is why your discharge rate is much lower than the 5 amps you have programmed. 10 watts limits you to about 1.4-1.5 amps when discharging a 7.x volt battery. You should get slightly higher rates as the battery voltage lowers. (watts = voltage x current in a DC circuit). The charger you have uses very common power limits and effectively matches the EVPeak CQ3 chargers I use. The HiTec X4AC chargers I have are limited to 5 watts, which was most common a couple years ago.. They now do more 'standby' duty than anything else.

    The capacity readings you're getting are not unusual. I have a set methodology I use for testing all modules, whether they be Gen 1, 2, 3 or 4, old or new. As long as your methodology is consistent, it is a very effective tool for comparison. It's very frequent that some modules, from the same OEM pack, have different capacities. I've had some Gen 2 packs that test as good or better than much newer Gen 3 packs. It greatly depends on how used and abused the pack has been.
     
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  6. ericbecky

    ericbecky Hybrid Battery Hero

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    Tmr-jwap is correct. Consistency is the key.

    There is no way you are going to find somene able to match the profile of your modules. Cannot match your equipment nor your methodology. Likely the best you can do is make sure they aren't dead on arrival. Which it sounds like they weren't. That said1400mah and 3200mah modules are not likely to play well most cars.

    If you buy a large quantity of modules (hundreds?) you will be able to sort through them. And if you are lucky you might find some similar-ish to yours. But you might not. It really is luck of the draw.

    You are correct to not believe that your 14 year old modules are truly 6300mah.

    If you want someone to sell do some custom testing you would probably could pay extra for their time I suppose.

    When testing modules you may want to start with a charge cycle first. You never know how the cells within the modules are when start. Filling them all first makes sure you aren't to rough in the low ones.

    I'd be happy to discuss some other ideas with you on the phone. I and others here sell modules. I'm certainly not the cheapest. But you can be sure you aren't buying duds with crap capacity. Plus you get a resource for bouncing ideas off of. 608-729-4082 if you want to talk.
     
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  7. TMR-JWAP

    TMR-JWAP Senior Member

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    I am definitely going to have to throw an overwhelming load of real world test data into this thread...............

    here's a quick one...this is a portion of the spreadsheet for a battery I installed in a fellow forum members car on 11/24/2017. I purchased the HV battery out of a low mile 2016 wreck and used the modules to build his Gen 2 battery.

    Discharge 1 was the initial discharge performed immediately upon removing the module pack from the 2016 case. I ALWAYS discharge first to get an indication of the energy remaining in a each individual module. It's a great way to see if any stand out as having a potential self-discharge problem.,Since these batteries have been sitting for many months going through salvage processes, what better time to check it? It will stand out like a sore thumb. They were then charged and then another cycle. No more required after that.

    These numbers fall right in line with the values I got when I tested a brand new Gen 3 battery purchased when a Toyo dealer was selling off it's parts inventory. Anyone remember when I scored those 2 new, still in the shipping container HV batteries?

    Prius 2016.jpg
     
    #7 TMR-JWAP, May 6, 2019
    Last edited: May 6, 2019
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  8. wnrsm

    wnrsm Junior Member

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    Thankfully the whole thing looks clean. I'm rather sure I have some inconsistent/failing modules. The rehydrating thread has some age to it.
     
  9. wnrsm

    wnrsm Junior Member

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    @TMR-JWAP and @ericbecky thank you for all that information!

    About the capacity readings appearing to be high for an old battery...

    The charger is set to wait five minutes when going from charge to discharge. Perhaps it would be more accurate to measure mAh capacity by letting the modules sit for a day or two after charging before performing the measured discharge.

    Ignorant question here - Why is there no common/standard way to measure battery health and capacity? If it were simple and easy we would have it already. A battery stores and delivers a measureable amount of energy. Can we constrain the variables (temperature, wire gauge) to accurately describe battery capacity?

    I know this is over-simplified and wrong - where's the error here? - Charge the battery, let it rest 24h, measure mAh output during a 1A discharge down to 6V. Does this fail to work because chargers are inconsistent?
     
  10. TMR-JWAP

    TMR-JWAP Senior Member

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    wnrsm,

    I have 2 bags of #105 rubber bands. One bag is 14 years old. The other bag I just purchased yesterday right off the manufacturing line. What kind of characteristics are important for a rubber band? I suppose it could be elasticity, flexibility, etc. The factory has specific QC standards it must apply in a final testing phase to verify each batch meets those minimum requirements so they can say that bag of rubber bands meets specification. You and I don't know exactly what those tests are, but we can make our own. I can measure its dimensions, I can measure the hardness of the rubber, I can make a rig to stretch the rubber band and measure its length and the tension that was applied when it finally snaps. I can record it's length achieved at immediately before it snaps. If I apply my test to all the brand new rubber bands I'll get a specific set of values. This becomes my "standard" for comparison. If I now apply that same exact test sequence to the 14 year old bag of rubber bands, I should have results that I can compare to my "standard". I can use that 'length immediately before it snaps' as a standard. Some of the old rubber bands snap at 50% of the stretch length, some at 75% and some make it full length. Some make full length and meet the other test comparison criteria. Are they not good rubber bands?

    If I take a brand new battery module and perform a specific set of tests on it, and then perform the same set of tests on other modules, I can use those numbers to determine how well those other modules compare to a new one. It is what it is. If a 14 year old module tests at 10% of a new one, would you believe it? What about 20% or 50% or 75%? If it tests at 95% of a new module, guess what? It is what it is. That's why the world has standards for testing and comparison.

    That 14 year old module may have had a relatively easy life. There's plenty out there that haven't and there's plenty out there that have.

    Following a standard test procedure will sort them out. That's why you're getting the measurements you have. You're using the same exact test for each module. That's all you need to do in order to sort good from bad. Absolute accuracy doesn't matter. You just need equivalent results using your test methodology to get 28 modules that are similar.
     
  11. TMR-JWAP

    TMR-JWAP Senior Member

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    Ignorant question here - Why is there no common/standard way to measure battery health and capacity?

    I believe there are ways. I have an electronic, hand held tester for checking 12v battery health. They're all over the place and pretty affordable. Plenty of demand for them, so plenty of supply, makes and models. As for 7.2v NiMH modules used in Toyotas? Not so much demand. They would be prohibitively expensive for you and I. There are battery test devices out there that can work on just about any battery, but not in the normal person's price range. Take a look at 2k1Toaster's thread about the HV battery he developed. He has some test equipment that will do exactly what you discuss, but batteries are his business (or one of).

    If it were simple and easy we would have it already. A battery stores and delivers a measureable amount of energy. Can we constrain the variables (temperature, wire gauge) to accurately describe battery capacity?


    Absolutely. We do it by having a "standard" for comparison and using an identical test method. From that, we can compare our results to the "standard".

    I know this is over-simplified and wrong - where's the error here?

    Not wrong at all. This is as close as the typical person can get without spending a fortune on specific diagnostic and test equipment. In our case, does it matter if the actual capacity as measured by a $100k machine is 5% different than what we measure with ours? Especially if all we're looking for is similar results from identical test procedures? If your settings stay unchanged, a charger/discharger uses the same calculations every time to determine the mAh discharged or charged. There's no gray area.

    - Charge the battery, let it rest 24h, measure mAh output during a 1A discharge down to 6V. Does this fail to work because chargers are inconsistent?

    I discharge first, as explained above. I programmed a 20 minute rest between the end of discharge and start of charge. Since I only perform one cycle at a time, and they typically start at 530 am and 530 pm, they normally get about 2 hours of rest before the next cycle starts. My test bench is set up with a prius fan and ductwork supplying cooling air flow, so the modules never have a large temperature cycle. They do typically get a little warm at the top of the charge cycle, as expected.

    As for inconsistencies, I would say they are insignificant. The majority of chargers are duplicates of each other and they probably all use the same algorithms / etc for doing the measurements and checks.

    A battery stores and delivers a measureable amount of energy.

    That says it all, right there. As long as you measure each battery using an identical method, the results are valid for comparison purposes. Exact accuracy doesn't matter.


    Another example.

    I have an OTC 3184(?) model 12v battery tester. You have a Solar BA5 model 12v battery tester. I bet they would both provide near identical CCA readings when testing the same battery.

    An SKS model Prius 12v battery is CCA rated at 325, but normally tests at 475 or better when new. As they age, this CCA test results drops. Is it still a good battery when it tests at 375? 325? or 250? or 150? at what point does it become a bad battery? All of those can be a well functioning battery, as long as each internal cell is ~equal to the others. Maybe you can leave your headlights on for only 10 minutes instead of 60 before it drains, but it's still a functioning battery. It becomes a BAD battery when one internal cell fails or becomes extremely weak compared to the others.

    This is why a Prius can still work just fine and get 48 mpg, even with a very weak HV battery. The HV system normally operates in a ~22% band SOC from ~64% SOC to 42% SOC. As long as there are no failed modules or modules significantly weaker than the others, all a module has to do is act normal for that band. It's why having a balanced pack is important. Having 28 modules with measured capacity of 6200 is great. Having 28 modules with 3000 capacity is not great, but it's also ok. The car won't know the difference because they are balanced and will charge/discharge ~equally when under load and won't have a significant variation in voltage from each other. What the car does know, is if you have 27 modules at 6200 and one at 3000. That 3000mAh module will change voltage much faster than the others and that delta V will be detected by the ecu.
     
    #11 TMR-JWAP, May 7, 2019
    Last edited: May 7, 2019
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  12. wnrsm

    wnrsm Junior Member

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    FYI for anybody's search for a Horizon Hobby Prophet Sport Quad Charger DYNC2050 - Maybe this will show up in a google search and save somebody the trouble. Prophet Sport Quad 4 X 100W AC/DC Charger | HorizonHobby

    My Prophet quad charger is showing >6800mAh capacity for some modules, which is higher than original/new. The Turnigy chargers report much lower numbers, which must be more accurate.

    I contacted HorizonHobby and asked about this accuracy. I was told two things:
    1) It is safe to discharge NiMH to zero volts.
    2) All that really matters is battery voltage.

    Here's their reply, pasted verbatim. I can't make this up.

    "We certainly appreciate you reaching out to product support. What matters is the voltage in almost all situations. If the battery is getting to the proper charge voltage and or discharge storage values.
    NiMAH batteries as you may already know, can go as low as 0.0v and still accept a charge. Values like the 'Percentage' or the 'Mah" values may be slightly skewed. The numbers that truly matter are the voltages.
    The voltage at the start of the charge, and the end of the charge. "

    This is the kind of support I would expect from AliExpress vendors for a product that cost 25% of a legitimate product.
     
  13. TMR-JWAP

    TMR-JWAP Senior Member

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