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bq27426 battery capacity

Jonathan CONSTANT
Prodigy 110 points
Other Parts Discussed in Thread: BQ27426, BQSTUDIO, BQ27220, BQ27546-G1

Hello,

I would like to use the bq27426 for a 10000 mAh 3.7V battery. 

In the datasheet the max battery capacity of the bq27426 is 14000mAh (www.ti.com/.../BQ27426) but in the document SLUUBB0 p. 49 ( http://www.ti.com/lit/ug/sluubb0/sluubb0.pdf ) the max value of design capacity is 8000mAh. Where is the error ?

Thank you.

  • 0
    TI__Expert 4450 points

    Hello Jonathan,

    Do you have a bq27426 on hand?  You could test this, link your EVM to computer, add 3.7V power supply to Pack+,Pack-, open bqstudio, then try to modify the capacity to 10000. If bqstudio reminds you that the value has beyond the range, it means it does not support more than 8000mAh.

    I am so sorry I don not have a bq27426 on hand, so I could not do this for you.

    Best regards,

    Sammi Shang

  • 0 in reply to Sammi Shang
    Prodigy 110 points
    Hello Sammi,
    Thank you for your answer. I don't have bq27426 on hand, I wanted to know if it can support my battery before ordering one...
  • 0 in reply to Jonathan CONSTANT
    TI__Expert 4450 points
    Hi Jonathan,

    It is 8000mAh max, I use the bqstudio, try to write 10000 to design capacity, but it reminds me that beyond maximum value.
    What requirement do you have of gauge? Maybe you could choose another one.

    Best regards,
    Sammi Shang
  • 0 in reply to Sammi Shang
    Prodigy 110 points

    Hi Sammi,

    I am using a 10000mAh, 3.7V battery and I would like a pre-programmed chemistry profile. I need I2C communication for programming the fuel gauge with Design Capacity. Maybe the bq27220 could be a solution ? If I understand there is no learning cycle, the system must go through a full charge and then a full discharge cycle to correctly configure the gauge ? I just need to modify the design capacity parameter or do I need to change more parameters ? 

    Thank you for your help.

    Best Regards, Jonathan

  • 0 in reply to Jonathan CONSTANT
    TI__Expert 4450 points
    Hi Jonathan,

    BQ27220 is a CEDV gauge, it need not to do self learning cycle, but as you said, it need to go through a full charge and discharge cycle to update FCC. For IT algorithm gauge, it need self-learning cycle. You may need to modify design capacity, design energy, taper current, termination voltage.

    Best regards,
    Sammi
  • 0 in reply to Sammi Shang
    Genius 5512 points
    hi Sammy,

    Does that means bq27426 max only can reach 8000mAH instead of the 14000 mAH as stated in TI website?

    rgds,
    kpk
  • 0 in reply to Poh Kok Keng
    TI__Expert 4065 points
    Hi,
    Yes bq27426 Design Capacity can only be set up to 8000mAh and the reason for that is bq27426 requires 4 battery parameters: Design Capacity, Design Energy = (design capacity x design voltage), Terminate Voltage, and Taper Rate.
    For your battery case, your design capacity is 14000mAh which will be ok for Design Capacity register size, but it will be out of range for Design Energy register size limited to 32767 mWh, (14000mAh x 3.7V = 51800 mWh) and that's why we need to keep the Design Capacity within 8000 mAh, no issues for other parameters.
    I can recommend other gauges that uses Impedance Track technology if I can get more information about your application requirement other than than battery capacity, for example gauge size or gauge communication contrarians in addition to cost.

    Regards,
    Haidar
  • 0 in reply to Haidar Hamoo
    Genius 5512 points
    hi Haidar,

    End application is network tester and below is the battery detail:

    Battery Pack details as below,
    3.7v Nominal Voltage ( Max 4.2v)
    13200mAh Capacity ( 6 cells in parallel)
    Need I2C read/write access

    Please help to recommend.

    Best Regards,
    kpk
  • 0 in reply to Poh Kok Keng
    TI__Expert 4065 points
    Hi kpk,

    I would recommend bq27546-G1 fuel gauge since it can fit your design capacity requirement, communication requirement, and this device has additional features that bq27426 lacks like Internal Short Detection and Tab Disconnection Detection. I also wanted to mention that after double checking bq27426 TRM pages 44,45 you may be able to use bq27426 gauge but you have to scale your design capacity value by 10, please check this out and also check bq27546-G1 features. Thank you for selecting TI devices in your system design, please do not hesitate to post any question or questions you may still have.
    regards,
    Haidar