Gen 2 possible HV battery restoration in vehicle

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by JohnStef, May 3, 2023.

  1. JohnStef

    JohnStef Member

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    I have four Gen 2 Prius in my care for family members, three have HV battery packs that are below 50% capacity, one of these throws a red triangle from time to time. I have rebuilt the packs in two vehicles a total three times. it is a lot of work to pull that sucker and reinstall. My research about the Gen 2 and 3 HV battery shows that there is no BMS. Toyota's approach was to assemble packs with carefully matched cells to keep blade voltages very close over years of service. A BMS would have been an improvement for 200k+ vehicles now commonplace. One of mine is 371k and I suspect it is the original pack. I do a lot of highway driving.

    Since the Prius does not naturally go thru a deep discharge/charge cycle blade voltages and module voltages can and do diverge and the pack becomes out of balance.

    My suggested In-Vehicle Restoration is to discharge the HV battery as far as the ECU will allow, and Force Recharge to fill the battery to 100%. Then repeat two times.

    I do not know what the lowest voltage the ECU will allow and start the ICE to begin recharging. I see in Toyota HV battery spec sheet that the normal low voltage is 180v. But ideally the discharge would approach 168v. From what I have read, the ideal low voltage to deep cycle a NIMH battery is 1v per cell. There are 168 cells in 28 modules, hence a target of 168v.

    How can the car draw the battery down to this target voltage with little or no disassembly?
    Will the car start the ICE and recharge itself at or near 168V?
     
    #1 JohnStef, May 3, 2023
  2. alftoy

    alftoy Senior Member

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    #2 alftoy, May 3, 2023
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  3. Tombukt2

    Tombukt2 Senior Member

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    Your pack is generally a 211 volt system so you can hook up a halogen 500 w light You know one of those silly work lights before LEDs and that should pull it down right quick and if you were in Europe and you had it 240 volt bulb for that market that would work too from from Venice hybrid chargers I have his discharger right here sitting on the floor it involves connecting some kind of hydrol lamp or whatever a heat lamp will work
     
    #3 Tombukt2, May 3, 2023
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  4. JohnStef

    JohnStef Member

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    I emailed the folks at Dr. Prius and posed this question to them, their reply was "at 168v the error code will be triggered and the battery ECU will not allow the car to be powered up in order to protect the inverter and the motor"

    So I am moving on and will read the thread posted above to build a charger/discharger. Thank you alftoy and Tombukt2
     
    #4 JohnStef, May 3, 2023
  5. dolj

    dolj Senior Member

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    This probably is for the best. I don't believe what you proposed would have worked as the battery ECU would not allow the battery to be charged more than 80% or discharged 40% in-car.

    In the Gen 2, there is a way to discharge the battery below 40% in-car by putting the car in neutral but that is a risky procedure in the wrong hands. Further, turning the car off when it is so badly discharged will not allow the car to restart. It is a bit pointless doing this as the car will never recharge above 80% which is required to top balance. As far as reconditioning goes, your only good option would be to make or purchase external charging and discharging equipment and do the reconditioning externally.
     
    #5 dolj, May 4, 2023
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  6. Tombukt2

    Tombukt2 Senior Member

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    I Don't have much trouble heave hoing the battery out of the car It's undoing all the stinking little bolts behind the seat. So when I take the battery out once or think I'm going to and I get those bolts that are in between the backs of the back seats and the metal frame those don't ever go back in so the bolts on the battery are only attached on the top and the rear edges now One of the little trays on one of the sides I get rid of that too this is just in my car because I thought I might be doing this dance a few times but then I realized that would be out of the question just because it didn't make sense to me. So I got a new battery prepped all the bus bars and all of that stuff put it back in left the bolts out like I do and the battery's been running great no problems and the plastics are back covering all of that and I've just left it alone for about a year or so been running great.
     
    #6 Tombukt2, May 4, 2023
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