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HV Battery Rebuild - Cell Capacity and Balancing Help

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Kenneth Steere, Apr 25, 2014.

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  1. Kenneth Steere

    Kenneth Steere New Member

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    Please no one tell me I should buy a already rebuilt unit...I'm not going to do that now. Too far in.
    I tried replacing 1 or 2 cells when they went bad and that has happened 3 times now in one year.
    I know, that was a bad idea. I did not balance the cells or even capacity test them...now I will as the pack is overheating after about 30-60 mins driving.

    This is my plan. Tell me what I need to do to improve it. Thanks! (contacts have been cleaned good)
    I have ordered some DC6 chargers, but am using a 6amp charge / 2amp discharge Hobby Charger. (Traxxas EZ-Peak Plus)
    It does not have a voltage cutoff though for charging, so I would have to monitor charging until I get the DC6's. I have decided to DISCHARGE-TEST all cells as they all have equal voltages now from the car charging- about 7.8v each. I am discharge testing to 6.8v for a max of 2 hours and charting each. The unit is discharging @ 1.2
    My Steps: (that need improvement I'm sure)
    1. Leave cells in pack to maintain compression. Some cells are newer than others.
    2. Discharge test each cell @ 1.2A for 120 mins max. Target voltage is 6.8v.
    3. Note each capacity (Ma/h) and replace bad cells, match others to balance.
    4. Recharge each cell to around 8v each.
    Here is a chart I prepared to track this first test. Note the capacities vary greatly!
    I'm sure this is why it is overheating as this is WAY out of balance.
    Note: Each discharge will only run up to [email protected] or 6.8v, whichever comes first.
    [​IMG]
     
    #1 Kenneth Steere, Apr 25, 2014
  2. ericbecky

    ericbecky Hybrid Battery Hero

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    Kenneth, You are in a tough spot. Do you have a way to test/see the module voltages while it is in the car? This way you can better see what is going on live under real conditions. Do you know which are the ones causing the overheating?

    Capacity is fine to measure, but how do they do under a heavy load? Not sure what you have handy, bit even a 40amp load would help. Testing for internal resistance.

    I would not charge them with a 6amp load. Way too high for a topping charge.
     
    #2 ericbecky, Apr 26, 2014
  3. Easy Rider

    Easy Rider Active Member

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    If you have had multiple cell failures, that odds are GREAT that all or most of them are getting weak.
    Continuing down your present path likely is an exercise in futility; in the end, a waste of time and money.

    You seem to KNOW that and yet you persist.
    WHY ??

    The mark of a really good soldier is not only being a fierce fighter but also knowing when to retreat. :)
     
    #3 Easy Rider, Apr 27, 2014
  4. bisco

    bisco cookie crumbler

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    welcome to priuschat how many miles on her?
     
    #4 bisco, Apr 27, 2014
  5. SageBrush

    SageBrush Senior Member

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    The Android app 'Torque,' along with a BlueTooth OBDII dongle will let you monitor voltage and resistance of the modules while you drive. The App will collect the data for export to a Spreadsheet. You can even correlate it to total traction battery Amp flow if you want to get fancy.
     
    #5 SageBrush, Apr 27, 2014
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  6. ericbecky

    ericbecky Hybrid Battery Hero

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    If you don't have it apart right now, Sagebrush makes a good suggestion for getting some data so you aren't flying blind. Would be less than the chargers.
     
    #6 ericbecky, Apr 27, 2014
  7. Kenneth Steere

    Kenneth Steere New Member

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    Sagebrush: Thank you for usable information. I will try that app after I get it back in.
    I have a MOTO G Android, but I thought the Bluetooth was only for phone calling...
     
    #7 Kenneth Steere, Apr 28, 2014
  8. SageBrush

    SageBrush Senior Member

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    I have the same phone. It works great with this BT OBDII dongle.

    There are cheaper ones you can consider, but I figured that this is a case of spending some money to get a high quality gadget, and since I wanted to leave it attached to the port I chose one that does not drain power when the car is off.
     
    #8 SageBrush, Apr 28, 2014
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  9. Kenneth Steere

    Kenneth Steere New Member

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    Easy Rider:

    "If you have had multiple cell failures, that odds are GREAT that all or most of them are getting weak."
    That's why MOST of them have been replaced now and I am weeding out the rest.

    "Continuing down your present path likely is an exercise in futility; in the end, a waste of time and money."
    I am NOT proceeding down the same road. I was not even testing their capacity the last times.
    I can tell by my chart it was terribly out of balance. Not this time!
    This time I am testing their Ma/h capacity and will be matching them in pairs by MaH and ending V.

    I'm doing this because I ENJOY doing this kind of thing(computer tech) and also saving money.
     
    #9 Kenneth Steere, Apr 28, 2014
  10. ericbecky

    ericbecky Hybrid Battery Hero

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    I've said before that this can be an enjoyable hobby.
    But often people don't have the luxury of extra time to be without their vehicle.
    Like any project you do yourself, you will learn a lot.

    But if ever stops being fun, that's when you should bow out.
    Too often mistakes occur when frustration sets in.
    And with Prius packs, you don't have too much leeway for mistakes.

    Keep plugging away in a systematic manner, tracking exactly what you are doing.
    You'll be happy later that you kept good notes!

    Sending positive thoughts your way!
     
    #10 ericbecky, Apr 28, 2014
  11. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    PC user scotman27 is doing a rebuild in the Gen I forum right now. I highly suggest you read his thread and follow along with that. He is doing an excellent job imo. It is a little verbose but, tons of good info there.

    Here's a link
    got some young 2012 modules | PriusChat
     
    #11 usnavystgc, Apr 28, 2014
  12. Kenneth Steere

    Kenneth Steere New Member

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    Bisco: Thank you. I have 2004 Prius with about 110,000 miles on her now. Yes, most of the cells that are old are going to be bad and have been failing. I am replacing most of them, including some cells I got out of a 2013 Prius pull. I know they have to be matched, by capacity, in pairs, and that's what I'm doing using excel to help me sort.
    Here is a preliminary copy of my sorted cells spreadsheet. Note that similar capacities are paired.
    [​IMG]
     
    #12 Kenneth Steere, Apr 28, 2014
  13. ericbecky

    ericbecky Hybrid Battery Hero

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    Consistency is the key.
    Do not switch your testing procedures midway through.

    Even if your process is flawed, it will be consistently flawed and you can still compare one set of data to another.

    Even a stopped clock is right twice a day.
     
    #13 ericbecky, Apr 28, 2014
  14. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    The thing that concerns me is that the first 18 modules didn't even make it to the 120 min mark. Eric, you are the expert, don't you think all the modules should be run thru three charge/discharge cycles to get an accurate capacity measurement for pairing?
     
    #14 usnavystgc, Apr 28, 2014
  15. ericbecky

    ericbecky Hybrid Battery Hero

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    There are as many opinions on how to do it as there are people who are embarking on this adventure. :)
    Some say 1, some say 3, some say 5. Well if 5 is good what about 7 or 9? :) At some point you begin to have diminishing returns.

    To me as long as you have a consistent way of doing what you are doing you'll get the process down and weed out some of the bad cells.

    The only Achilles Heel is when your process is flawed enough that it doesn't actually identify the bad cells. For example ones with high internal resistance often are missed because they are discharged in a way that glosses over their resistance.
     
    #15 ericbecky, Apr 28, 2014
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  16. Kenneth Steere

    Kenneth Steere New Member

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    erikbecky: That is my main concern as well (internal resistance). I am staying consistent for sure. All the cells were at what I assume to be a steady state of charge from the vehicle. They all were initially measuring the same voltage around 7.8v each. For consideration of time, and that they were all at a steady state from the car, I proceeded to only Discharge test each cell to 6.8 each or a max of 120 mins @ 1.2a (whichever came first). You can see the 2013 cells didn't even get under 7v in 120mins. Monsters!
    I am concerned about internal resistance though, but are not sure how to test for that...
    Thanks!
    Ken
     
    #16 Kenneth Steere, Apr 28, 2014
  17. Kenneth Steere

    Kenneth Steere New Member

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    I just wanted to report that my method has been a complete success so far.
    All Cells were paired and I purchased 4 more pulled from 2010 and 2013 (gen3)
    There is no more overheating. No more loss of initial power in the mornings.
    I simply eliminated the lowest rated (MaH) cells from the pack and paired the rest.
    Now using Torque Pro for Android with the Prius Gen2 mods I can monitor
    all the 14 blocks and even check internal resistance predicting problems before they happen.
    It's a good thing. :) Ken
     
    #17 Kenneth Steere, May 4, 2014
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  18. nh7o

    nh7o Off grid since 1980

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    Good to know that you are happy with your success, and thanks for adding to the knowledge base. These adventures are becoming less so all the time.
     
    #18 nh7o, May 4, 2014
  19. ericbecky

    ericbecky Hybrid Battery Hero

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    Ken, Could you do the community favor and check back in from time to time?
    I know often people need to go back in and do the process as they identify new "bad actors" in the pack.
    I want people to have some reasonable expectations based on real-world experience like yours.

    Thanks in advance!
     
    #19 ericbecky, May 4, 2014
    Last edited: May 27, 2014
  20. Kenneth Steere

    Kenneth Steere New Member

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    I have to report that I am having a problem with overheating.
    If I am getting new cells that are 5000MaH and most of my older ones are 4000MaH or less am I going to have to get rid of all the older ones to get together 28 that are VERY close in their MaH?
    I tried using Gen 3 cells and they were really to powerful compared to mine, so I went back to Gen 2 only.
    I however still see the pack overheat in the middle after over an hour driving in the heat with air conditioning.
    The OBD sensor showed up to 125F even thought the voltages were apparently constant though the SOC had dropped some.
    Could that temp be incorrect? The fan didn't seem to come on, even at the high temp.
    I did have the cover off the battery though... How close do the capacities need to match?
     
    #20 Kenneth Steere, May 24, 2014
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