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BQ20Z95: Cell balancing failure and full discharging during shipment

Avi Katav
Prodigy 50 points

Part Number: BQ20Z95

Hi,

We are using 2S1P LI-PO cell (4000mA) connected to PCM(BMS) board (attached schematic).

Our battery = 7.4V@4000mA.

 

Recently, we encountered large amount of failure (50%) with new batteries.

50% of our failure related to:

    1. cell balancing failure.
    1. full discharging during shipment.
    1. Low capacity.

 

We are looking for the root cause.

 

Questions:

  1. Can it be related to GG file configuration (attached)?
  2. Has anyone encountered similar issue before with 2S1P with BQ20Z95?
  3. Can it be related to PCM board (attached schematic) or cells?
  4. Our Min Cell Deviation register set to = 1750 (supporting cell balancing) can it be related to failures?

BQ20Z95_PCM Schematic.pdf

1385.BQ20Z95_PCM Schematic.pdf

 Thanks,

Avi

 

  • 0
    Prodigy 50 points

    Attached GG file.

    https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/2S1P_5F00_BQ20Z95_5F00_GG_5F00_10012018.7z

  • 0 in reply to Avi Katav
    TI__Mastermind 25955 points
    Hi Avi,

    Please also send a quick log or series of logs of the device(s) exhibiting:

    1. cell balancing failure
    2. full discharging during shipment
    3. low capacity

    Thanks!

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 50 points

    Hi Bryan,

    Thanks for the fast reply.

    Attached example of one of the battery log snapshot using TI SW.

    This is after air shipment.

    Please advise if you need more information.

    Thanks,

    Avi

     

  • 0 in reply to Avi Katav
    TI__Mastermind 25955 points
    Hi Avi,

    Thank you for the image of the registers, schematic, and gg file.

    Could you also send a few text logs from some of the affected devices and mark them based upon the mechanism of failure: (1) cell balancing (2) full discharging during shipment (3) low capacity.

    Also, for some more background information on the issue:

    1) How many packs have you shipped before the 50% failure rate?
    2) How many packs are experiencing the 50% failure rate?
    3) Has anything changed in the design of the packs prior to experiencing failures?
    4) Has anything changed in the layout of the packs prior to experiencing failures?
    5) Has anything changed in the components of the packs prior to experiencing failures?
    6) Has anything changed in the batteries of the packs prior to experiencing failures?
    7) Has anything changed in the gauge dataflash of the packs prior to experiencing failures?

    In short, have there been any changes? Deltas are very helpful in tracing problems :)

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Prodigy 50 points

    Hi Bryan,

     

    Please see my comments inline.

     

    Thanks,

    Avi

    Thank you for the image of the registers, schematic, and gg file.

    Could you also send a few text logs from some of the affected devices and mark them based upon the mechanism of failure: (1) cell balancing (2) full discharging during shipment (3) low capacity.

    Also, for some more background information on the issue:

    1) How many packs have you shipped before the 50% failure rate?

    [Avi] For the last 3 years we are shipping by air and sea around 3K yearly.


    2) How many packs are experiencing the 50% failure rate?

    [Avi] In the last 3 shipments (each around 1K pcs) from China to Israel we got 50% failure.


    3) Has anything changed in the design of the packs prior to experiencing failures?

    We updated the procedure before the last shipment and it did not help.


    4) Has anything changed in the layout of the packs prior to experiencing failures?

    [Avi] No, nothing changed.


    5) Has anything changed in the components of the packs prior to experiencing failures?

    [Avi] No, nothing changed.


    6) Has anything changed in the batteries of the packs prior to experiencing failures?

    [Avi] No, nothing changed.


    7) Has anything changed in the gauge dataflash of the packs prior to experiencing failures?

    [Avi] No, nothing changed.

    In short, have there been any changes? Deltas are very helpful in tracing problems :)

     

    [Avi] Nothing that I can recall.

  • 0 in reply to Avi Katav
    TI__Mastermind 25955 points
    Hi Avi,

    Thank you for the inline comments - as asked previously, could you please send the logs of the failing devices, corresponding gg file, and modality of failure?

    The screenshot of the registers does not give me enough information to analyze the device or begin to determine a root cause.

    If you would prefer not to disclose the logs publicly, we can continue internally with e-mails.

    Sincerely,
    Bryan Kahler