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BQ27220EVM-744: Battery remaining capacity change after load connect

hitesh soramiya
Prodigy 145 points
Part Number: BQ27220EVM-744
Other Parts Discussed in Thread: BQ27220, BQSTUDIO, EV2400

Hello,

Hope you are doing well.

We are using BQ27220EVM-744. Without load remaining capacity(RC) 1119mAh show higher but after load connect it goes to 89mAh. in sequence aging remove load readings show after 89mAh.

if we remove battery and connect again reading follow upper sequence(without load 1119mAh, with load 89mAh....)

Could you please tell us this are correct or not because we calculate percentage using remain capacity?

is there any other option to get or calculate battery percentage?

Please find attached readings for your reference.

Fullscreen 05092023 bat reading.txt Download 
05-09-2023



Serial port COM5 opened
Time Count(per 10sec) 23   BQ27220 Voltage = 0 mV Current = 0 mA RC = 0 TTE = 0 TTF = 0

Whithout load

Time Count(per 10sec) 24   BQ27220 Voltage = 3609 mV Current = 0 mA RC = 1119 TTE = 65535 TTF = 65535
Time Count(per 10sec) 25   BQ27220 Voltage = 3609 mV Current = 0 mA RC = 1119 TTE = 65535 TTF = 65535
Time Count(per 10sec) 26   BQ27220 Voltage = 3609 mV Current = 0 mA RC = 1119 TTE = 65535 TTF = 65535
Time Count(per 10sec) 27   BQ27220 Voltage = 3609 mV Current = 0 mA RC = 1119 TTE = 65535 TTF = 65535
Time Count(per 10sec) 28   BQ27220 Voltage = 3609 mV Current = 0 mA RC = 1119 TTE = 65535 TTF = 65535
Time Count(per 10sec) 29   BQ27220 Voltage = 3609 mV Current = 0 mA RC = 1119 TTE = 65535 TTF = 65535

With load

Time Count(per 10sec) 30   BQ27220 Voltage = 3609 mV Current = -85 mA RC = 210 TTE = 1145 TTF = 65535
Time Count(per 10sec) 31   BQ27220 Voltage = 3569 mV Current = -239 mA RC = 89 TTE = 43 TTF = 65535
Time Count(per 10sec) 32   BQ27220 Voltage = 3569 mV Current = -238 mA RC = 89 TTE = 30 TTF = 65535
Time Count(per 10sec) 33   BQ27220 Voltage = 3568 mV Current = -238 mA RC = 88 TTE = 25 TTF = 65535
Time Count(per 10sec) 34   BQ27220 Voltage = 3567 mV Current = -238 mA RC = 87 TTE = 23 TTF = 65535
Time Count(per 10sec) 35   BQ27220 Voltage = 3567 mV Current = -237 mA RC = 87 TTE = 23 TTF = 65535
Time Count(per 10sec) 36   BQ27220 Voltage = 3566 mV Current = -237 mA RC = 86 TTE = 22 TTF = 65535
Time Count(per 10sec) 37   BQ27220 Voltage = 3566 mV Current = -237 mA RC = 85 TTE = 22 TTF = 65535
Time Count(per 10sec) 38   BQ27220 Voltage = 3566 mV Current = -237 mA RC = 85 TTE = 22 TTF = 65535
Time Count(per 10sec) 39   BQ27220 Voltage = 3565 mV Current = -237 mA RC = 84 TTE = 21 TTF = 65535

Whithout load

Time Count(per 10sec) 40   BQ27220 Voltage = 3603 mV Current = 0 mA RC = 83 TTE = 24 TTF = 65535
Time Count(per 10sec) 41   BQ27220 Voltage = 3603 mV Current = 0 mA RC = 83 TTE = 45 TTF = 65535
Time Count(per 10sec) 42   BQ27220 Voltage = 3603 mV Current = 0 mA RC = 83 TTE = 89 TTF = 65535
Time Count(per 10sec) 43   BQ27220 Voltage = 3604 mV Current = 0 mA RC = 83 TTE = 178 TTF = 65535
Time Count(per 10sec) 44   BQ27220 Voltage = 3604 mV Current = 0 mA RC = 83 TTE = 356 TTF = 65535
Time Count(per 10sec) 45   BQ27220 Voltage = 3605 mV Current = 0 mA RC = 83 TTE = 711 TTF = 65535
Time Count(per 10sec) 46   BQ27220 Voltage = 3605 mV Current = 0 mA RC = 83 TTE = 1245 TTF = 65535

With LED load 

Time Count(per 10sec) 47   BQ27220 Voltage = 3605 mV Current = -7 mA RC = 83 TTE = 1245 TTF = 65535
Time Count(per 10sec) 48   BQ27220 Voltage = 3605 mV Current = -7 mA RC = 83 TTE = 1245 TTF = 65535
Time Count(per 10sec) 49   BQ27220 Voltage = 3605 mV Current = -7 mA RC = 83 TTE = 711 TTF = 65535
Time Count(per 10sec) 50   BQ27220 Voltage = 3605 mV Current = -7 mA RC = 83 TTE = 711 TTF = 65535

Whithout load

Time Count(per 10sec) 51   BQ27220 Voltage = 3607 mV Current = 0 mA RC = 83 TTE = 1245 TTF = 65535
Time Count(per 10sec) 52   BQ27220 Voltage = 3607 mV Current = 0 mA RC = 83 TTE = 2490 TTF = 65535

With load

Time Count(per 10sec) 53   BQ27220 Voltage = 3569 mV Current = -238 mA RC = 83 TTE = 111 TTF = 65535
Time Count(per 10sec) 54   BQ27220 Voltage = 3567 mV Current = -237 mA RC = 83 TTE = 36 TTF = 65535
Time Count(per 10sec) 55   BQ27220 Voltage = 3566 mV Current = -237 mA RC = 82 TTE = 26 TTF = 65535
Time Count(per 10sec) 56   BQ27220 Voltage = 3565 mV Current = -237 mA RC = 81 TTE = 23 TTF = 65535
Time Count(per 10sec) 57   BQ27220 Voltage = 3565 mV Current = -237 mA RC = 81 TTE = 22 TTF = 65535
Time Count(per 10sec) 58   BQ27220 Voltage = 3565 mV Current = -236 mA RC = 80 TTE = 21 TTF = 65535
Time Count(per 10sec) 59   BQ27220 Voltage = 3564 mV Current = -236 mA RC = 79 TTE = 20 TTF = 65535
Time Count(per 10sec) 60   BQ27220 Voltage = 3601 mV Current = 0 mA RC = 79 TTE = 22 TTF = 65535
Time Count(per 10sec) 61   BQ27220 Voltage = 3602 mV Current = 0 mA RC = 79 TTE = 44 TTF = 65535
Serial port COM5 closed
Serial port COM5 opened
Time Count(per 10sec) 74   BQ27220 Voltage = 3605 mV Current = 0 mA RC = 79 TTE = 65535 TTF = 65535
Time Count(per 10sec) 75   BQ27220 Voltage = 3605 mV Current = 0 mA RC = 79 TTE = 65535 TTF = 65535

Remove Battery

Time Count(per 10sec) 76   BQ27220 Voltage = 2997 mV Current = 2997 mA RC = 2997 TTE = 2997 TTF = 2997
Time Count(per 10sec) 77   BQ27220 Voltage = 3700 mV Current = 0 mA RC = 0 TTE = 0 TTF = 0
Time Count(per 10sec) 78   BQ27220 Voltage = 3606 mV Current = 0 mA RC = 1096 TTE = 65535 TTF = 65535
Time Count(per 10sec) 79   BQ27220 Voltage = 3606 mV Current = 0 mA RC = 1096 TTE = 65535 TTF = 65535
Serial port COM5 closed

   

 

  • 0
    TI__Guru 57697 points

    Hello Hitesh,

    Due to labor day holiday, responses may be delayed

  • 0
    TI__Guru 61536 points

    What's the capacity of the battery?

    Please make sure that you set EDV2/1 to the correct values for 7% and 3% SOC.

  • 0 in reply to Dominik Hartl11
    Prodigy 145 points

    Li-ion, 3.7V, 2.6Ah.

  • 0 in reply to hitesh soramiya
    TI__Guru 61536 points

    Did you try a discharge with your configuration and the bq27220 EVM connected to bqStudio instead of your host uC and log all registers with bqStudio (Register Log)?

    The gauge calculates RM = FCC - coulomb count. FCC is measured during a qualified discharge and it should be around 2600mAh for you cell. If RM is 89mAh, then the gauge counted FCC-89mAh coulombs from a full charge. The gauge doesn't use voltage to calculate RM. It uses coulomb count. So if there's a RM that doesn't look reasonable for a specific voltage, we'd have to know FCC and coulomb count (passed charge) from a full charge.

    Note that the gauge estimates RM with a voltage measurement when the gauge is reset and that can be inaccurate, if the cell isn't relaxed and the 10 point voltage table isn't configured correctly. Are you getting 100% SOC when charging stops for a full charge? What's FCC and RM in this case?

  • 0 in reply to Dominik Hartl11
    Prodigy 145 points

    Hello Dominik,

    We don't have EV2300/EV2400, so not able to use bqstudio.

    Could you please describe more about coulomb count?

    What is 0 point voltage table? we not configure any voltage table. when the RM is 3000mAh then the value of SOC is 100.

  • 0 in reply to hitesh soramiya
    TI__Mastermind 27321 points

    Hi Hitesh,

    It would be easier to configure the gauge using BQStudio. Highly recommend to obtain an EV2400 if you can.

    Coulomb count represents the passed charge either when you charge or discharge. The gauge will measure the current of the battery and integrate the current over time. This way, it will know how much the battery has been charged or discharged.

    The gauge comes with a pre-defined voltage table. However, this OCV table does not account for the specific cell you are using. We have characterized thousands of cells over the years, it is most likely that we have a similar match of your cell chemistry in our database. Please use the GPCCEDV tool to obtain the OCV table. Note that this tool also outputs some parameters for temperature optimization in case your application requires it.

    See below for default OCV table in data memory. 


    Regards,
    Jose Couso