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BQ27542-G1: Remaining life

Takashi Yamaguchi
Genius 13290 points
Part Number: BQ27542-G1

Hi team,

I received a question about bq27542-G1 from my customer.

Could you tell me how to calculate the remaining life? Customer checked the data sheet, but they didn't understand how to involve the parameters of SOH and Load to the calculation of remaining life. 

Regards,

Yamaguchi

  • 0
    TI__Guru** 105590 points

    Hello Takashi,

    Could you define what they are looking for with the remaining life? the State of Health will give the percentage of the maximum capacity of the battery at that time. SOH should be 100% with a new system and derease over time. They would need to determine what percent SOH is acceptable for the system and that would help determine how long the system's overall life would be.

    The percentage remaining during each discharge would be the SOC.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Genius 13290 points

    Hello Wyatt,

    Thank you for the answer. 

    For the remaining life(SOH), I checked what customer is looking for. Could you support the following questions?

    1. Calculation formula

    The customer understands from the data sheet below that SOH is calculated by dividing the charge capacity by the design capacity, and applying a correction(compensation). However, customer doesn’t know what kind of correction(compensation) method is used in it, so customer would like to know it. Especially, could you tell us how the parameter of “SOH Load I” affects to the correction(compensation)?

     

    2. Update condition of SOH

    Could you tell me what is the condition for updating SOH? Is it updated every certain time, or is it updated when certain conditions of discharge and charge (cycle count etc.) are met?

    Customer faces an issue that Remeing Life becomes less than 100 even though the cycle count is 1 with BQ27542-G1. 

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Mastermind 24870 points

    Hello Yamaguchi-san,

    SOH is computed by the same engine that computes RemCap, however we fix the load current so it does not change via the dynamic learning during the discharge.

    SOH Load I will be a constant variable that is used in a RemCap simulation.

  • 0 in reply to Kang Kang
    TI__Genius 13290 points

    Hi Kang-san,

    Thank you for the answer.

    Regarding the SOH calculation, is it possible to show the calculation formula concretely?

    Also, could you tell me the conditions and timing when the SOH value is updated?

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Genius 13290 points

    Hi Kang-san,

    Customer would like to know the answer soon, so could you support the questions above?

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Guru** 105590 points

    Hello Yamaguchi-san,

    The formula for the SOH should be the following: SOH = (Design Capacity)/(FCC Simulated with SOH load 1)

    I believe the conditions would be updated whenever a new FCC is calculated after a cycle.

    Let me verify this and let you know.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    TI__Genius 13290 points

    Hi Wyatt-san,

    Thank you for your support. I informed it to the customer, but they don't understand how to calculate the  "FCC Simulated with SOH load 1". Therefore, could you tell me the specific calculation?

    For example, how much SOH will be in the case below?
    Design Capacity:3000mAh
    FCC: 2800mAH
    SOH Load I:-400mA

    Regards,

    Yamaguchi

  • 0 in reply to Takashi Yamaguchi
    TI__Mastermind 24870 points

    Hello Yamaguchi-san,

    It really depends on the Qmax and Ra tables.

    https://www.ti.com/lit/an/slua364b/slua364b.pdf?HQS=slua364-aaj&ts=1591998301457&ref_url=https%253A%252F%252Fwww.google.com%252F

    This app note shows a RemCap simulation example. The SOH is the same thing except it uses SOH Load I instead of what we use in load mode/select.

    Thanks