Inconsistent Hybrid battery readings

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Mike A L, Nov 3, 2020.

  1. Mike A L

    Mike A L New Member

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    About a month ago my Gen II Prius got the dreaded 3 warning lights. A local mechanic ran diagnostics and found that Block 4 was "bad". I ordered OEM cells, took the battery apart and used a multimeter to find out which blade in the block was bad. I replaced the one with only 6.68v charge. Put the whole thing back together and installed it. By this time I had an ODB II scanner. Drove the car, same lights, used the OBD II, same issue (block 4). Took it apart again and replaced the other blade. Put it all back together again.
    Next time I drove it, the same warrning lights came on. When I used the OBD II reader, this time it told me block 12 was bad. Didn't tell me that before. Block 4 was apparently fine.
    I had just received a grid charger, installed it and ran it for about 24 hours. Drove again, same issue, same block (12). I ordered a light bulb discharger, it arrived and I discharged the battery nearly completely. Ran the grid charger for 24 hours again.
    When I drove next, a different issue happened. The fuse in the grid charger harness blew, even though nothing was connected. This caused all the lights to go on and this time the OBD II reader showed block 12 AND 13 were bad.
    This weekend I took the battery out again and used the multimeter to find out which blades were bad. I tested every blade 3 times. The lowest voltage was 7.77 and the highest was 7.82. So the largest variation was only 5/100 of a volt! That battery was about as balanced as it could be. The charger had done exactly what it was supposed to. So I didn't change anything, just reinstalled the battery.
    Drove it today. After about a mile the warning lights came on again. Get home, OBD II... block 8 is bad. Not 12 or 13 anymore, even though I didn't do ANYTHING to the battery.
    How is this even possible? Any ideas?
     
  2. bisco

    bisco cookie crumbler

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    sounds like the classic whack a mole. sometimes you just need a new battery
     
  3. JC91006

    JC91006 Senior Member

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    There really is a skill in rebuilding a battery properly, it's not as easy and fast as what you've described.

    Since you seem to have all the right equipment to do this, you should let the battery sit a week before taking any measurements, so it'll allow to discharge. The bad modules will discharge a lot more than good modules.

    Afterward you can load test the good ones and see if they are all good. Then button everything back up with all good modules and balance the entire pack using your charger/discharger
     
    jerrymildred and Raytheeagle like this.
  4. TMR-JWAP

    TMR-JWAP Senior Member

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    Think of it like this. When your battery was brand new, it was like having 28 brand new 'D' cell batteries. The HV battery ecu continuously monitors the 14 block voltages looking for a voltage difference between blocks that exceeds its setpoint threshold. Over the years, with thousands of temperature cycles and thousands of discharge/charge cycles, those 'D' cell batteries have degraded. Some are now 'C' cells, some are 'AA' cells and some are 'AAA' cells. Since the car uses only a very small band of capacity during normal operation, the car can usually function just fine with those cells. Unfortunately, one dropped down to a 'hearing aid' battery with very little capacity or had an internal failure. That's the one that finally tripped the threshold and coded the battery. That is the one you found that was 6.x volts. What did you replace it with? If you replaced it with a module that is a 'D' cell, then those 4 or 5 'AAA' cells are now going to randomly trigger the threshold. Even though they would probably work fine if a 'C' or 'AA' used module was installed, a replacement module that has a high capacity will make the others look weaker than they really are. Hence the term whack-a-mole. This shows the importance of matching a replacement module to the estimated average capacity of the remaining original modules.

    Pick 28 random people off the street and line them up side by side, with their height differences monitored by a computer. Remove the shortest one from the lineup and replace him with Lebron James. The computer does not trigger a code for being too tall, because it only looks for "too short". Now, the new shortest guy (or 5) looks like a problem to the computer....

    If you remove the shortest person and then pick a replacement who is the same height as the average of the other 27, he just blends in
     
  5. HybridCPR

    HybridCPR Junior Member

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    I really enjoyed your explanation, just hilarious. Wondrous. It is actually a great way to (perhaps) ease the non-technical to formulate some idea of what is occurring.
     
    #5 HybridCPR, Nov 9, 2020
    Last edited by a moderator: Nov 9, 2020
  6. HybridCPR

    HybridCPR Junior Member

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    When these batteries are created in the factory, all modules in the HV battery have chemicals etc from the same batch, same shift, same day, etc. So they are exquisitely balanced, perform together amazingly well. !0 years later, they have been heated up, cooled down, been discharged/charged hundreds of thousands of times. The original amperage capacity has diminished over time and use, may be down to 30%, 20%, 15% of original. A failure of one---essentially means the others will follow shortly. How could they not? If you catch them before failure, they can usually be reconditioned to 70% or so of original. Module (cell) shorts, however, are hard to predict (when a 7.5V module drops to 6V or so)
     
  7. Chba

    Chba Junior Member

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    I find your explanations very clear, thank you for that.
    I am very sorry to see that I made an unnecessary investment of over $ 1000 by purchasing a "Prolong Deluxe charger / discharger" and 7 modules at 6000mAh.

    I discharged the pack up to 134V which normally corresponds to an individual voltage of 4.8V per module. Here in image, the results of the measurements. All modules purchased have a voltage greater than 7v. Others are less than 4.8V. There is a huge difference in capacity between cells.
    Before replacing the modules, I had no P0A80 fault code although their capacity was low.

    Tell me, if there is a possibility of combining the high capacity modules with the low capacity ones, to form balanced blocks? 20210308_202922.jpeg

    Posted via the PriusChat mobile app.
     
  8. Whalerpaul1

    Whalerpaul1 New Member

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    Are those low voltage ones even usable?... Hoping for a response from a knowledgeable member.

    Important missing information here is the capacity per module. That is a pretty similar across the 28 modules you'll be pulling codes.

    Personally I would take this opportunity to upgrade all of the week sales based on discharge capacity.
     
  9. Whalerpaul1

    Whalerpaul1 New Member

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    If the capacities are not pretty similar across all the modules, you will be pulling codes. I think it will be worth several hundreds of dollars to get newish similar capacity modules.
     
  10. TMR-JWAP

    TMR-JWAP Senior Member

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    You need to rethink about how the Prolong System works. The goal of the system is to 'help' the weak modules by cycling them. Strong modules don't need any help, right? The thought of a target discharge voltage corresponding to an average module voltage needs to thrown out the window.

    After 15 years, your 28 new modules are now allover the place with regard to capacity. Some are still 6000, some 5000, 4000, 3000, 2000 or even 1000 or less. Which ones do you care most about improving? Probably not the 6000 or 5000 ones right?

    When the Prolong starts discharging the modules:
    1. All modules are participating in the discharge because they're in series. Whatever amount of current flows through one module also flows through all the others, whether it be charging or discharging.
    2. Keeping #1 in mind, the module with the lowest capacity "empties" first. Then the next lowest and then the next lowest and so on.
    3. Overall pack voltage is slowly decreasing the entire time. The vast majority of this decrease is due to the weak modules depleting and their voltages dropping more quickly than 'good' modules. These may be the 1000 and 2000mah capacity modules. A good module will plateau for a while at ~7.2 volts. The better the module, the longer the plateau will hold.
    4. As the weaker modules deplete, you eventually reach the low voltage setpoint and the Prolong discharge stops. At this point, the weakest of the modules are fully depleted and the strongest modules have not been significantly affected and are likely to still be at the 7.2 volt plateau.

    Now we start the Prolong charge cycle:
    1. Again, all modules are charged at the same exact amperage.
    2. Essentially, the module with the lowest capacity will be the one to reach full capacity first. Any module that reaches full capacity will just convert any additional charge current into heat while the remaining modules continue to charge.
    3. Eventually, all modules will reach full capacity and the upper limit voltage of the charge will be reached and the charge can be stopped.
    Now we start the next discharge cycle, except this time, Prolong recommends the low voltage limit be even lower than the first discharge. Why? Because now, the worst of the weak modules have been cycled and we can now try to also catch some of the next tier of "weak" modules. Now maybe we'll be able to get some of the 3000 capacity modules. The third cycle will be to an even lower final voltage. Maybe it will catch some of the 4000 capacity modules. And all during those second and third cycles, the modules from the first cycle are getting worked again.

    Hopefully, by the time the three cycles are done, the worst of the weak modules have been worked the hardest, the semi-weak modules have been worked a moderate amount and the not-so weak modules have been worked a little. The strong modules? While the other modules are getting the workout of their lives, the strong modules are just chillin with a cold one, just along for the ride.

    Always remember a grid charge system WILL NOT fix a FAILED module. There's no reliable cure for an internally failed module except module replacement with a good one.
     
    #10 TMR-JWAP, Nov 4, 2021
    Last edited: Nov 4, 2021
    mr_guy_mann likes this.
  11. Tombukt2

    Tombukt2 Active Member

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    Your time is money everyone's time is you figure out what you can afford The doctor Prius or the factory 1600 dollar pack for as long as they last it's just for me the way to go and once I've modified my brackets and I'm keeping the car after that if I ever do it again the battery change will be 14 minutes long because not near of the car has to come apart again . There's no replacement for new cells new electric cars don't get refurbed batteries they get new batteries and they cost but that's just part of it

    SM-A715F ?
     
  12. Another

    Another Active Member

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    Time spent is usually important. If it’s not, keep working on it. Otherwise, if you’re planning on trying to keep car for five years more, get an OEM battery. For keeping it three years, get a Greentec with new cells. If planning on getting rid of it soon, get the cheapest solution you can find. Piece of mind with the OEM is a plus. But with a Gen 2 never knows when the Grim Reaper will arrive with either a massive inverter or other problem or a stolen or totaled car accident.
     
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