TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker and becoming a Supporting Member. For more info: Support TMC
Start a Discussionhttps://teslamotorsclub.com/tmc/tags/

Effect of a cell failure on the whole battery pack

Discussion in 'Model S: Battery & Charging' started by Tuyuq, Aug 3, 2017.

  1. Tuyuq

    Tuyuq New Member

    Joined:
    Aug 3, 2017
    Messages:
    2
    Location:
    Jo
    Hi

    I want to ask what would happen if one or more cells in the same "in-parallel" module fails, how would this affect the other cells in the same module under high current demand like insane mode etc.



    Thanks!
     
  2. SabrToothSqrl

    SabrToothSqrl Active Member

    Joined:
    Dec 5, 2014
    Messages:
    2,006
    Location:
    PA
    Well, you'd call your service center and they'd fix it... :)
    Thus ends my desire to fix anything on my car. Hence my 6 year 100,000 bumper 2 bumper warranty.
     
  3. chibi_kurochan

    Joined:
    Jan 20, 2017
    Messages:
    130
    Location:
    San Jose, CA
    take this with a grain of salt, quoting a source who worked on the BMS:
    "0.1% capacity loss for every 7 (cell failures) out of 7000 cells in a module, it will look like normal degradation"
     
  4. mongo

    mongo Member

    Joined:
    May 3, 2017
    Messages:
    355
    Location:
    Michigan
    based on a wk057 tear down of a 85kWh 400V pack, the cells are set up in groups of ~72 cells in parallel. The BMS is is going to limit pack discharge/charge based on the lowest/ highest voltage sub-module. With less cell, the failed sub module will be the fastest charging/ discharging portion of the pack.

    If one cell fails open, or shorts and causes the fuse wire to open, the usable pack capacity will drop about 1.4%, assuming no active recharge from the battery management system (BMS).

    If the cell fails as a partial short and pulls more current than the BMS can balance, the pack will ultimately fail.
     
  5. Tuyuq

    Tuyuq New Member

    Joined:
    Aug 3, 2017
    Messages:
    2
    Location:
    Jo
    [QUOTE="mongo, post: 2233152, member: 60387"

    If one cell fails open, or shorts and causes the fuse wire to open, the usable pack capacity will drop about 1.4%, assuming no active recharge from the battery management system (BMS).

    If the cell fails as a partial short and pulls more current than the BMS can balance, the pack will ultimately fail.[/QUOTE]


    I find that very interesting,
    If more than 1 cell fail in the same module, will it decrease the amperage of the whole pack or will the car use the same amperage during Ludicrous Mode , or will the BMS limit the available amperage and high power usage would be limited?
    I don't know what amp rating of the 18650 used in the Tesla, but I assumed its 10A per cell so 720A max per module
     
  6. mongo

    mongo Member

    Joined:
    May 3, 2017
    Messages:
    355
    Location:
    Michigan

    I find that very interesting,
    If more than 1 cell fail in the same module, will it decrease the amperage of the whole pack or will the car use the same amperage during Ludicrous Mode , or will the BMS limit the available amperage and high power usage would be limited?
    I don't know what amp rating of the 18650 used in the Tesla, but I assumed its 10A per cell so 720A max per module[/QUOTE]


    Interesting question.

    I see two possibilities: The first is that the BMS detects the failed cell by the increased rate of change of voltage of the sub pack compared to the rest of the module. It would then communicate the new current limit to the inverter.

    The second option is that the BMS does not detect the missing cell. Then the rest of the cells in the sub-module are subjected to a proportionately higher current draw and the sub-module voltage droop is higher and limits the peak current output (for lower states of charge).
     

Share This Page