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BQ27421-G1: State of Charge not corresponding to actual state on charge after a succesful learning

Matteo Mariani
Prodigy 60 points
Part Number: BQ27421-G1

Good day,

We have succesfully performed a learning cycle using a bq27421-G1A dev board using GDK hardware and battery managment studio software.

It went well according to software, but perfoming a validation run of several charge/ relax/ discharge/ relax cycles, to verifiy compliance of SOC value, we obtained this strange result:

Green line is SOC and as you can see it goes to 99% way sooner than actual full charge as per voltage and current values.

SOC on Discharge seems ok.

I sent log to Gauge parameter calculator to check CHEM ID discrepancy between the one embedded into the gauge chip and the actual one of our cell. Here it is the report we received:

Best chemical ID : 242 Best chemical ID max. deviation, % : 2.56



Summary of all IDs with max. DOD deviation below 3%

Chem ID max DOD error, % Max R deviation, ratio
242 2.56 0.28
257 2.58 0.32
5977 2.78 0.31
5917 2.99 0.23

Max. deviations for best ID is within recommended range. Chosen best chemical ID is suitable for programming the gauge.


Selection of best generic ID for ROM based devices like bq274xx


Device / Family #1
Generic Chem ID Device/ Voltage/ Chemistry max DOD error, %
354 bq27411-G1C: 4.35V LiCoO2 15.93
3142 bq27421-G1D: 4.4V LiCoO2 18.65
128 bq27421-G1A: 4.2V LiCoO2 36.94
312 bq27421-G1B: 4.3V LiCoO2 41.28
Best generic ID 354
Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule

It seems that the A version has an DOD error of 36.94%, while the D version only 18.65%

Is it possibile that chemistry discrepancy could cause such behavior?

Attached you can find validation cycle log file and data memory export.

 validation.log4336.data_memory.gg.csv

Thanks and best regards

Matteo

 

  • 0
    TI__Mastermind 24956 points

    Hello Matteo,

    The bq27421-G1A uses ChemID - 128, and your cell chemistry matches to ChemID - 242 in our database. I went ahead and compared these two in DOD error%. The highest possible DOD error % allowed for good gauging is 3%.



    As seen above, the DOD error goes up to 40%. 

    The bq27421-G1A is a ROM based gauge which has a fixed ChemID and cannot be program to multiple ChemIDs we have in our database.

    Two solutions:
    - Keep same gauge, but obtain a cell chemistry similar to ChemID - 128 


    - Obtain a flash based gauge, and keep same cell chemistry you have. These type of gauges can be programmed to multiple ChemIDs.

    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    Prodigy 60 points

    Thanks!

    Going from the 40% to the 20% of the version D could make any difference in your opinion?

    We can easily swap version of the same gauge, but change it with another part number it is really impractical.

    Any clue on how to ask to a cell manufacturer for a specific chemistry profile?

    Thanks and best regards

    Matteo

  • +1 in reply to Matteo Mariani
    TI__Mastermind 24956 points

    Hello Matteo,

    20% is still high DOD% error as the highest allowed is 3%.

    Matteo Mariani said:
    We can easily swap version of the same gauge, but change it with another part number it is really impractical.

    Swapping versions on this gauge does not change ROM based and all versions use a fixed Chemical Chemistry.

    Matteo Mariani said:
    Any clue on how to ask to a cell manufacturer for a specific chemistry profile?

    The information about ChemID-128 is:


    Description Known Compatible Cell (not exclusive) Cell type
    LiCoO2/carbon 5-1, -20C Sony: custom laminate (1200 mAh),HYB: ICR18650NH  laminate


    Regards,
    Jose Couso