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BQ4050: State-of-Health Function

Antonio Fadhel
Genius 9410 points
Part Number: BQ4050
Other Parts Discussed in Thread: BQSTUDIO, BQ40Z50-R1

Hi,

My customer is using the BQ4050 and would like to charge to only ~90% in the field to extend the lifetime of the battery. However, they would like to make sure it does not reflect an incorrect state-of-health reading. Which parameters should they change in order to do this? I was thinking they could just change Design Capacity to the lower SOC they plan to charge to, but the TRM states it uses a different SOH function without going into much detail. Are there any other parameters they would need to change? Another idea would be to just increase the termination current to avoid charging the last few %, but I assume this would still cause an incorrect SOH reading. 

If the above are not recommended, would increasing the Near Full parameter to ensure qualified discharges while charging to a lower voltage result in accurate SOC? I.e. would it show their fully charged cell at ~90% rather than update FCC as the lower capacity and show a correct SOH?

Thanks,

Antonio

  • 0
    TI__Expert 6575 points
    Hi Antonio,
    On bq4050, the SOH is FCC/Design Capacity.
    There shouldn't be any issue with reducing the charging Voltage to extend the life of the pack.
    Reducing the Design Capacity by an appropriate amount should reflect a reasonable SOH value, except if there are sudden large loads or extended low temperature operations that will significantly drop the FCC.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 220 points

    Hello Swami,

    Thank you very much for your reply. If I change the design capacity, would I also require to change the R0 parameter? Or since the capacity is only reduced to update the SOH effectively R0 remains the same?

    Best regards,

    Luis

  • 0 in reply to Luis Pinillos
    Prodigy 220 points

    Hello Swami,

    Sorry to bother you, do you have any news about this? I changed the charging voltage so that the SoH update occurs at the new specified voltage, but there are some discrepancies at around 50% of SoC. I was thinking that maybe the DoD table needs to be updated to the new range?

    Please tell me what you think about this. I really appreciate your help.

    Best regards,

  • 0 in reply to Luis Pinillos
    TI__Expert 6575 points
    Hi Luis,
    The Design capacity will not affect gauging as such, it is only used for the SOH calculation, so R0 does not have to be changed.
    Please post a bqStudio log and your gg file for the SOC discrepancy, because it will be hard to speculate the cause of the issue without the log and knowing the settings.
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 220 points

    Hello Swami,

    Sorry for the late reply, it took me a while to be able to log a cycle.

    Attached find the .gg and .log files, as additional information, we are using a 3S9P battery pack using cells that are 3.65V nominal voltage and 2.75Ah capacity. The current is divided in two so that the gauge is able to handle the battery pack.

    Thank you very much for the help.

    If you need me to provide any thing else don't hesitate to ask.

    Best regards,

    Luis

  • 0 in reply to Luis Pinillos
    TI__Expert 6575 points
    Hi Luis,
    After looking at the log and gg file, I think my advice earlier might have not been correct.
    I think there are two things that are causing your issue:
    1. The FCC has never updated. This is likely because the pack was never cycled from 0 to 100% or 100% to at least 3%. Once FCC automatically updates, you should see "Max Error" change from 100% to 2%
    2. You have disabled CEDV ([BIT3] of CEDV gauging configuration is set to 0), so either you will have to select the EDV2, EDV1 and EDV0 thresholds, or enable it and get the CEDV coefficients using the CEDV online calculator at http://www.ti.com/tool/GPCCEDV by submitting six logs. The current scaling will be automatically accounted for by this online tool, so that should not be an issue.

    But primarily, the FCC needs to update before you will get valid gauging results. There is more information on the FCC update in section 6.3 of the TRM ( www.ti.com/.../sluuaq3 )
    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Intellectual 285 points

    Hi,

     two questions ask:

    1. About OperationStatus register ,from the BQ40Z50-r1 Technical Reference,i knwon that,it has two way to access,one is used   0x54 register  ,another way is ManufacturerBlockAccess() or ManufacturerData(),

         These two way can read the same results?

    2.How to read ManufacturerAccess() 0x0054 OperationStatus register? is the same as below? First write command 0x00,data sent 0x0054,then read command 0x23?

    Thanks!

  • 0
    Intellectual 285 points

    Manufacturer Access  enter 0010，but device（bq20z75）can not enter into shutdown mode,why?

  • 0 in reply to Libing Huang
    Prodigy 220 points

    Hi,

    From what I have worked with the BQ40z50-R1, you can get the value of the register using any of those methods, just take into account the the ManufacturerAccess() uses the 0x00 command, then the data sent using Big Endian, and to read the value you send command 0x23. If you wish to read ManufacturerBlockAccess() you use command 0x44 then send the adress you wish to read in little endian (54 00 in your case) and then use command 0x44 again to read. The ManufacturerBlockAccess() will give you the address first and then the value of the register. For example after reading you will receive 54 00 XX XX XX XX where each X is the data in the register.

    I hope this helps you.

  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 220 points
    Hi Swami,

    Thank you for the feedback, I will cycle the battery pack after these changes. We had already provided the 6 cycles, but the cycles reached the whole operating voltage of our battery. Would we need to do this again?

    In the meantime I am cycling the battery to update FCC and with bit 3 of CEDV gauging configuration set. I will provide the log to you as soon as it is finished.

    Best regards,

    Luis
  • 0 in reply to Luis Pinillos
    Intellectual 285 points
    Hi
    Thanks for your answer. I can read OperationStatus register with SBS cmd 0x54,also ManufacturerAccess()0x 0054?
    Do you mean that? Thanks!
  • 0 in reply to Libing Huang
    Prodigy 220 points

    Hi

    Yes, but in both of those cases you will need to read the ManufacturerData() sending 0x23.

    I hope this helps you.