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BQ40Z50-R2: Several vital questions about gauge configuration

Ivan Tokarev
Prodigy 70 points
Part Number: BQ40Z50-R2

Hello, TI.

Can you please answer several questions.

1. Can you give me explanation how to properly configure SoH Load Rate to achieve adequete SoH status? I know that setting defines current that is used in SOH simulation. I have 2S battery with 3000 mAh capacity. My load is very dynamic but I assume that my average current is 6A. Should I make SoH Load Rate = 0.5 as referenced in formula in TRM？  . Note that minimum value that can I write to this setting in connected battery is 0.1 and maximum is 25 for some reason.

2. Am I right that Term Voltage setting is used in capacity calculation algorithm(You call it Impedance Tracking algorithm) as lowest voltage boundary(simulates % so that when Term Voltage was reached, battery must output 0%)? And Full Discharge Voltage Thresholds(Gas Gauging -> FD -> ... Threshold) are only used for FD flag indication and doesn't affect on capacity algorithm?

Keep in touch, 

Ivan

  • 0
    TI__Guru** 105590 points

    Hello Ivan,

    The SOH Load Rate is in units of 0.1hr, this means you should set it to 5, this indicates to the gauge the discharge rate is 3000mAh/(5*0.1hr) = 6000mA.

    Yes the Term Voltage is the value the gauge uses to simulate 0% SOC (RemCap = 0mAh) The FD flag can be set using different settings and is not necessarily directly linked with the terminate voltage since you can set or clear the FD flag based on voltage or RSOC.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hello, Wyatt.
    Thanks for the answer.

    1. If I using Constant Power gauging mode, do I need to set up SoH Load Rate somehow differently or this settings only takes into account the current drawn from battery ant not the power?
    1.1 I know that my average drawn power in discharge is 70 Watts and my battery is 2S 21.6 Watts-hours, how can I apply it to my SoH settings?
    2. If SoH capacity(SoH FC@25 E or SoH FC@25 Q ) correlates with Full Charge Capacity? If my Full Charge Capacity was dropped, should SoH decreased too? 
    I know that FCC can suddenly drop due to high current discharging. I want to to understand what will happen with SoH in that worst scenario?

    Keep in touch,

    Ivan

  • 0 in reply to Ivan Tokarev
    TI__Guru** 105590 points

    Hello Ivan,

    The SOH Load Rate is only in terms of current, not power. Set it to the average power you expect to see during the discharge.

    The SOH FCC is the FCC calculated with the SOH Load Rate and using 25degC. If your Ra table or Qmax changes you should see SOH FCC update. Just because the FCC used for active gauging drops does not mean the SOH FCC should drop since each use different temperatures and different load currents for simulation. 

    Sincerely,

    Wyatt Keller