HV battery SOC issue

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Joao, Jan 24, 2021.

  1. Joao

    Joao New Member

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    Hi everyone, this is my first post, thank you so much for the endless info, that helped me a lot with multiple issues on my 2005 (299999km+). Last month my hv battery died and i decided i dint want to do te so called whack a mole repair. So i found a semi-new battery from a 2018 toyota, bought the 28 modules and replaced them all (using the old case of course). First few weeks the car ran fine, but now i have a curious issue. When i go on a long downhill, the car charges to "full" green bars, and when i start using the power, it almost instantly goes to a low SOC. Looking at hybrid assistant data, it seems that the car is incorrectly estimating SOC, because the module voltage never goes bellow 16v, eventually it will throw a p0a80, which goes away after i reset, only to return when the above pattern is done. While stationary, if i do a slow discharge, like using the ac at max cold, the battery seems to behave normally with a slow discharge. I have rechecked everything, torque the nuts again, cleaned the bus bars again, to no effect. Any idea of the root cause? Your help is appreciated!
     
  2. JC91006

    JC91006 Senior Member

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    Maybe the battery is not from a 2018? How were you able to determine the year on the modules you purchased?

    There are serial numbers on the battery modules, all 28 of the modules should have similar serial numbers. Make sure all of them are similar and not mixed. If you like, you can reply with the module's serial number and someone will help you determine the year of the modules.
     
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  3. rjparker

    rjparker Senior Member

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    My guess is one of the battery blocks suddenly goes low. Back to whack a mole.
     
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  4. TMR-JWAP

    TMR-JWAP Senior Member

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    Did you use a new wire frame #2 (the wire harness with all the sensing tabs and plugs into ECU) or reuse the old one? Did you inspect the plug sockets on the ecu? Have you verified all the connections/plugs are properly secured?
     
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  5. Joao

    Joao New Member

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    Thanks for the replies.
    yes, i checked the serial numbers, it was from a wrecked car. Also the newer modules (2016 and above, i believe) have a slightly different design in the top.

    i did reuse the old wire frame, some voltage sensor tabs had some corrosion but none were broken. I also double checked the connections. Do you think it might be an issue with an intermitent bad voltage reading? When i drive the car, the drop from normal soc (50-60) to sometimes 30% is pretty much instant.
    Thanks everyone
     
  6. edthefox5

    edthefox5 Senior Member

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    Did you pull the ecu can out and remove the printed circuit and look closely at it for corrosion?

    Or you just have a soft module. Back to whackin'.
     
  7. mr_guy_mann

    mr_guy_mann Member

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    Log the data with Hybrid Assistant while performing a test drive then look at the voltage graph in Reporter to see what block has voltage above or below the rest. Depending on what you see, one of your modules might be off or the wire frame might still be bad. If the voltages look fairly even then it could be a wonky battery ecu.

    Posted via the PriusChat mobile app.
     
  8. Joao

    Joao New Member

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    you mean the orange socket where all the voltage wires sensor conect? I didnt remove it, just checked it was righly connected, but i will check it.

    yes, i did this using hybrid assistant, all modules are within 0.3 V. Also while stationary i performed the battery health check (the one with max ac), the battery lasts a long time without the engine cutting in. It seems to me that the problems begin when there is high charge current involved and battery gets "full" (ie a longish downhill where regen braking os used) From then on, the battery soc just crazily jumps arround.
     
  9. Joao

    Joao New Member

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    searching the forum for possible issues i found this, and i noticed that my nuts are the old version (the left One on the picture). Does anyone know if a 2005 should have newer one? (The battery had been already messed with by previous owner)
     
  10. edthefox5

    edthefox5 Senior Member

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    No not the socket take that whole metal case out remove the metal covers and closely examine the circuit board both sides with a magnifier look at the connector pins from the board to the socket for whiskers. Anything suspicious take close pictures with iphone magnifier and post them here.
    Many reports and pictures of micro strands of wires we are calling whiskers coming off those socket legs which create path for corrosion.
     
  11. Joao

    Joao New Member

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    Ok thank you, will try to remove the ecu and check
     
  12. Joao

    Joao New Member

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    Checked ecu, no signs of corrosion. Do you guys think it can be the nuts on the terminals? They are quite black-ish, seems they lost the coating.
     
  13. mr_guy_mann

    mr_guy_mann Member

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    If you know the conditions that cause the problem to show up, then record data while you are driving like that. You want to see what the HV battery data for block voltages and State Of Charge when the gauge goes up and down.

    Posted via the PriusChat mobile app.
     
  14. jerrymildred

    jerrymildred Senior Member

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    This seems like the most likely explanation. Way more likely than a 3-year-old module just going bad all of a sudden.

    Terminal nuts are also a possibility due to either corrosion or incorrect torque. But the symptoms seem more indicative of a sensor wire issue.
     
  15. Joao

    Joao New Member

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    Thanks again for your replies
    unfortunately i didnt record a trip before opening the battery, but here is attached a report from hybrid assistant (doing the ac max test)

    i also think (and hope) this is the case. i have ordered the wire frame from toyota. You can see a picture attached, i cleaned the busbars but the nuts and voltage sensors are quite corroded. As you can see in the report, the middle cells have consistently lower voltages (min and max), so this may be an indication that the connections between modules is not good (?) (I reshuffled the modules before installing them, they were all showing the same voltage at that time)
     

    Attached Files:

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  16. Joao

    Joao New Member

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    1 month for toyota to get the parts (nuts are out of stock). If anyone in europe knows where i can find them (part 9291-47011) it is highly appreciated.
     
  17. TMR-JWAP

    TMR-JWAP Senior Member

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    Just off the top of my head, I seem to remember these being M5x0.8 thread. Any flange nut in that size will work. There's nothing special about the Toyota nuts, except their flange has a slightly larger diameter. I've built many batteries using the commonly available stainless steel flange nuts. The older style Gen 2 uses a nut with a integral crush washer (if that's the correct terminology), but the Gen 3 and later use the flange nut. If you kept the nuts from the Gen 4 battery, those will work perfectly.

    Here's something you can use for reference. A lot less expensive than Toyota also. Hopefully you have a hardware store or something similar available in your area. Make sure they have the 8mm size heads though. Oversize heads are available, but they'll prevent the black plastic arc guards from fitting correctly.

    A pack of 50 for 12 dollars.
    McMaster-Carr
     
    #17 TMR-JWAP, Feb 4, 2021
    Last edited: Feb 4, 2021
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