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BQ27510-G3, SOC, SOH, state of health

Yunfa Yang
Intellectual 515 points

I understood that battery capacity can't be determined instantaneously for a newly-inserted pack without some discharge activities being done  in a system-side fuel gauge setup. What about SOH? is SOH monitored in real time under Impedance Track? Does SOH updating require charge/discharge activities? How is percentage of SOH achieved, what factors impact SOH percentage? The SOH (0x1c/0x1d) unit is %/num, what does num stand for, discharging cycles? 

In my system, battery cell is for backup only, after it's fully charged there is no many activities, any suggestion for accurately monitoring SOC, SOH for my situation? Will be load test or certain charge/discharge activity be good for reliable SOC and SOH?

Regards,

Yunfa

  • 0
    TI__Expert 4115 points
    Hello Yunfa,

    SOH is broken up into % and num so that you can get the SOH percentage (i.e. 100%, 95%, etc.) and also the SOH Status (0x00, 0x01, 0x02 & 0x03). The SOH Status is a reflection on how accuracy the SOH percentage is. SOH is the calculated Full Charge Capacity (FCC) using SOH Load I as the load and room temperature divided by design capacity (Equation: FCC(SOH Load I, 25) / Design Capacity). In order to achieve an accurate SOH, you will want SOH Status to be 0x03. Upon initialization SOH Status should go to 0x01. SOH status can go from 0x01 to 0x02 after a resistance update or can go from 0x01 to 0x03 after a Qmax update. You could also see SOH Status go from 0x02 to 0x03 if there was first a resistance update and then a Qmax update. So, you do need to have some cycling in order to get the SOH value to update to an accurate value. Please refer to the Theory of Impedance Track application (SLUA450) for more details on FCC, resistance updates and Qmax updates.

    If you are using the gauge in your system as a back up we would recommend that you periodically run a "maintenance" cycle. That cycle would consist of relaxation so that the gauge can take an open circuit voltage (OCV) reading at the fully charged condition, discharging the battery by at least 37%, relaxing so that the gauge can take another OCV reading and then charging back to full. The two relaxation periods with the 37% passed charge in between allow the gauge to update Qmax and the discharge allows the gauge to update the resistance table.

    I hope this helps.