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StateOfHealth() from bq27545

Phien Nguyen Thanh22
Intellectual 570 points
Other Parts Discussed in Thread: BQSTUDIO

Hi all,

When i read SoH from bq27545 i am facing 2 problems

1. If i read SoH by command 0x2e/0x2f (StateOfHealth data),   return value is always 0 or > 65000.

2. So, I try reading FullChargeCapacity() to calculate SoH = FullChargeCapacity / DesignCapacity. But this SoH value is always change when i charge or discharge battery (over 30%). I can't understand how it estimate FullChargeCapacity.

Thanks for any help.

Phien Nguyen

  • 0
    TI__Guru 51346 points
    1: Do you read this with a uC or is this on an EVM with bqStudio? SOH is a integer with a range from 0 to 100.
    2: FCC is estimated by running an (automatic) discharge simulation with average current (or power - depending on configuration). It should not change that much (your observation indicates a problem).

    Did you obtain the ChemID through GPC? If so, what is the max DOD error?

    FCC is a function of many parameters, among them temperature, average current (or power) and age of the cell. If you run charge/discharge cycles at the same temperature and similar current then FCC should not change much from cycle to cycle (it will eventually drop because the internal impedances of the cell will rise as the cell ages).
  • 0 in reply to Dominik Hartl11
    Intellectual 570 points

    Hi Dominik,

    I read this with a uC, I think function read this info is OK. I can read FCC, cycle count, Remain Capacity, SoC, ... by this function. Do I need any special to read SOH? And is SoH equal to FFC/DesignCap *100 ?
    FFC if i don't run charge or discharge, it almost the same value, but when I run charge/discharge, it got a big change. The charge and discharge current are affect to FFC ?

    Thank you,
    Phien Nguyen

  • 0 in reply to Phien Nguyen Thanh22
    TI__Guru 51346 points
    You don't need anything special to read SOH.

    FCC is updated during charge and discharge. It is calculated based on remaining capacity simulations that are triggered during various depth of discharge points.

    Currents will affect FCC. For example, large currents will cause a big voltage drop over internal impedance, effectively limiting the amount of charge you can draw from the battery before it hits Vterm.