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Original question:

BQ34Z100-G1: SOH Calculation Mismatch with the actual state of Battery

BQ34Z100-G1: SOH Load 1 Value for Electric Vehicle Application

Anvin Arackal
Prodigy 240 points
Part Number: BQ34Z100-G1

Hi

I have been working on fixing the SOH inaccuracy as mentioned in this thread:https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1315791/bq34z100-g1-soh-calculation-mismatch-with-the-actual-state-of-battery

As suggested, the SOH Load 1 value was lowered according to the average load current instead of the maximum load current of the vehicle, i.e. 45A to 15A, and we noticed the SOH corrected from 91% to 96%. For further correcting the value of SOH to 100%, the SOH Load 1 value was further decreased to 6A and then 3A now. With this reduction of SOH Load 1 value, the SOH % derived from the gauge jumped to 97% and 98%.

To Summarize

SOH Load 1 Value          SOH Percentage
           45A                                 91%
           15A                                 96%
            6A                                  97%
            3A                                  98%


As per our testings, we have observed that noticeable Increase in SOH%. But there are concerns regarding this.

  1. Is lowering the SOH Load 1 Current value the right approach?  Since this is an EV application the average load current value is different for every discharge cycle. i.e. dependent on the driving pattern and the load of the vehicle itself.)
  2. What should be the correct value to be set for SOH Load 1 when all of the below scenarios can occur across different discharge cycles?  
    1. Scenario A: The vehicle is not used continuously and relaxed overnight. The Fuel gauge will be reading 0A for a long period. 



    2. Scenario B: The vehicle is used continuously with heavy load. The average current (0A to Max current of 45A) here for this discharge cycle will be higher.


    3. Scenario C: The vehicle may run continuously for a few minutes and then rest for the remaining few. The Fuel gauge will read 45A (max current) and 0A as well for different periods. i.e. The average current of the SOH Load 1 value is different for each discharge cycle.


  3. If it is incorrectly lowered to the bare minimum, what are the probable repercussions of this in the long run? Will any other values become erroneous as the Battery packs go along with the discharge cycles?

Please assist with the answers to the above three questions.

Regards

Anvin

  • 0
    TI__Mastermind 25665 points

    Hi Anvin,

    1) Lowering SOH Load will indicate that the average load applied to your battery is more than what was previously entered. Since your load varies, I recommend using the average discharge current on something similar to Scenario C. Or better take the average current of an expected discharge cycle for your application.

    2) I do not recommend writing to flash in the field this can cause problems. You can set SOH Load to whatever you want, the higher its set the more conversative the SOH calculation will be.

    3) If SOH Load is lowered to the bare minimum in the long run the battery may calculate a worse SOH than the actual health of the battery.

    Regards,

    Evan