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HV Battery charging question

Discussion in 'Gen 2 Prius Technical Discussion' started by JC91006, Jun 21, 2014.

  1. JC91006

    JC91006 Senior Member

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    I have been reading a bit about the hv battery rebalance threads and had a question. In charging the module up, it's recommended to over charge the cells so that if any cells within the modules are weaker, it would have the chance to charge up to the same level as the stronger cells. You would cycle this 3 times and it should balance out the cells, weaker ones should get to the level of the stronger ones.

    If this were the case, would it be beneficial to drive your car down a 10 mile downhill stretch (assuming you can find one) where your battery has the opportunity to overcharge (all 8 bars are completely full on the Battery meter)? (I know 8 bars is still only 80% full). I know this generates heat but wouldn't it be beneficial to overcharge the modules slightly to get the weaker cells to be a little stronger by overcharging? Go downhill as long as possible while the battery is at 8 bars. Do this every couple months to boost the battery performance and prevent the weaker cells to fail prematurely. This would be like an exercise (tuneup) for the battery without having it removed from the car.

    Does this make sense?
     
  2. ericbecky

    ericbecky Hybrid Battery Hero

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    It will not overcharge them since you are at 80%. It will simply stop the charge and burn off the extra.
     
  3. JC91006

    JC91006 Senior Member

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    but at 80%, all the cells can't be at the level correct? so my thinking is if you continue charging at 80%, the weaker cells that are not at 80% will get there by the long downhill charge?
     
  4. jeff652

    jeff652 Senior Member

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    When the strongest cells hits 80%, the car reads that as a full battery pack, and stops regen. So all but one cell will be below 80% SOC. You need a Grid Charger that can charge and balance the cells while the car is off, while still safely dissipating the 75+ watts of heat that will build up during balancing. This is only done properly by our patent pending charger systems that power and control the cars own hybrid battery cooling fan while rebalancing the battery cells.
     
  5. JC91006

    JC91006 Senior Member

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    How long does it take to rebalance a pack with your grid charger?
     
  6. jeff652

    jeff652 Senior Member

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    It takes ~1.5 hours to install the car harness (a one time activity) then the battery can be charge balanced in 24 hours or less in the car. If you deep cycle it with a discharge as well the process can be 2 days, so one charge-discharge-charge cycle can be easily done in a single weekend.

    [​IMG]
     
    Anthony Williams and Cloude1 like this.
  7. JC91006

    JC91006 Senior Member

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    I read that TampaPrius.com was using your grid charger on all his battery packs before installing it. Does this require the 1.5 hours to have that charger installed on all the cars and then uninstall it after the pack is charged?
     
  8. uart

    uart Senior Member

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    I believe that the 1.5 hrs is to install a wiring harness to allow quick "in car" connection in the future. For packs that are already out of the car the connection/disconnection would be much quicker.
     
  9. jeff652

    jeff652 Senior Member

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    Yes, this is correct. Out of car attachment is much faster.
     
    #9 jeff652, Jun 24, 2014
    Last edited: Jun 24, 2014
  10. JC91006

    JC91006 Senior Member

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    Jeff,

    Let's say you wanted to do this as a business.....sort of like a tune up for cars but this is a "balance up" for the hv battery. Would this be hard to do for a customer using your grid charger? Would every car be subject to the 1.5 hour install and balancing times for 24 to 48 hours?
     
  11. ericbecky

    ericbecky Hybrid Battery Hero

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    Yes. Balancing will always be at least 24 hours. I would say closer to 36 to do it right.
    Install a harness into the car. Then they drop it off for a top off.
     
  12. uart

    uart Senior Member

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    Hi Eric. What sort of charging current are you looking at to charge for that amount of time? Pretty low I'd assume. Would something like 150 mA be a ball park figure??
     
  13. JC91006

    JC91006 Senior Member

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    It would be nice to have a higher mileage 2004-2005 test subject car. Install this harness and top off every month, see how much longer it can go without the cells dying
     
  14. jeff652

    jeff652 Senior Member

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    Eric is right. With our current 350mA CC Grid Charger, times are in the 18-24 hour range. With our soon-to-be-released 3A PHEV charger/rebalancer, it will be much faster ;)
     
  15. ccdisce

    ccdisce Active Member

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    I have one of these grid chargers installed in a 2008 with 133Kmiles on the clock.
    On the HV battery I am not sure as the GREEN tape seal with the installer's stamp was cut, I bought the car used with 84Kmiles so the Battery computer or the Battery itself could have been changed.
    The plan was to re-balance---discharge---re-balance every 6 months and see if the MPG improves and the HV battery lifetime can be extended.
     
  16. JC91006

    JC91006 Senior Member

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    The green tape seal is cut on all of them I've seen. Without cutting it, you can't install the battery. Of course I've only seen 2 of them :)
     
  17. 2k1Toaster

    2k1Toaster Brand New Prius Batteries

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    How will you quantify "lifetime extended"? Will you do periodic Ah measurements? Because just going off of mileage means nothing. Some go 70K and fail. Some go 500K and still haven't failed.
     
  18. ccdisce

    ccdisce Active Member

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    The plan was to collect voltage, current vs time during the discharge phase to determine the capacity and see if changes over the next few years if it lasts that long.
     
  19. ccdisce

    ccdisce Active Member

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    Thanks for the info, it would seem that the HV Battery has 133Kmiles
     
  20. ccdisce

    ccdisce Active Member

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    I think that a sequence could be

    1. grid charge to 80%.
    2. discharge to 10% to reset battery memory and to measure capacity and log
    3. re-balance