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Original question:

BQ27750EVM-837: BQ27750

BQ27750EVM-837: BQ27750

M Schneider
Prodigy 95 points

Part Number: BQ27750EVM-837
Other Parts Discussed in Thread: BQSTUDIO, GPCCHEM

Hello,

I still have issues with the learning of the Fuel Gauge. The problem that I'm facing now is: I measure nearly 1A charge current more via the gauge, than it's actual going in to the battery.
The Shunt Resistor value is 1mOhm. Is there any calibration feature, or manual adjustment so I can correct this difference?



The value measured with a Multimeter is 1886-1889 mA.

Thanks for any help!

Martin

  • 0
    TI__Mastermind 27321 points

    Hello Martin,

    In bqStudio we have a current calibration feature where you simply enter the measured current from shunt resistor.



    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    Prodigy 95 points

    Hello Jose,

    Thank you, the calibration did work, the Gauge now measures the proper current and voltage values, but I still have an issue with the learning process:
    I fully discharged the battery, waited for the REST Flag and then I started charging. The problem is: the remaining capacity still grows twice as fast than it should be. The capacity off the Battery is 10.000 mAh. Charge current is about 2.1000 mA and after 15 Min charging the Remaining Capacity is 1000mAh, twice as high it should be.

    What is wrong with the setup?

    I logged the whole process:
    charge_log_one_cell_10000mAh.xlsx



    Can you please help me with this?

    Thank you!
    BR, Martin

  • 0 in reply to M Schneider
    TI__Mastermind 27321 points

    Hello Martin,

    I am glad the calibration worked.

    The jump in Remaining Capacity correlates with the jump in FCC.
    In your log file I see a jump in temperature of about 5C. This can cause gauging errors as Full Charge Capacity is the total amount of charge that the battery can deliver to a system for a specific set of conditions (average load, temperature).

    Also, did you use our GPCCHEM tool to find a good chemistry matching to your cell before attempting to do a learning cycle? Our ChemIDs contain a lookup table values for OCV readings. If the lookup table is off, the wrong OCV measurement will be taken, therefore, wrong Qmax, wrong FCC, wrong Remaining Capacity.

    Please follow this app note for learning cycles.

    https://www.ti.com/lit/an/slua777/slua777.pdf



    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    Prodigy 95 points

    I'm using a AA Power Corp Battery: High Power LFP Polymer Cell: 3.2V 10Ah (8790160-5C) 32Wh, 50A rate 




    That's the ChemID I'm using.

    The thermistor is attached to the battery.

    I did the learning along this app note you posted, so ChemID and gauging parameters were programmed.

    Any thoughts about this?

  • 0 in reply to M Schneider
    TI__Mastermind 27321 points

    Hello Martin,

    I cannot see the picture you posted. Please try a snippet or attach it again.

    M Schneider said:
    The thermistor is attached to the battery.


    Please make sure the TEMPS bit is set to external thermistor.

    Please attach the ChemID you are using.

    Regards,
    Jose Couso

  • 0 in reply to Jose Couso
    Prodigy 95 points


    ID is 0456
    It is set to external, if I'm touching the thermistor the temperature is increasing on the dash board. 

  • 0 in reply to M Schneider
    TI__Mastermind 27321 points

    Hello Martin,

    How did you obtain the ChemID? Did you use the GPCCHEM tool or did you match the exact manufacturer ID in the database?

    Regards,
    Jose Couso