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BQ78350-R1: How to set Fixed EDV0/1/2 ?

Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, GPCCEDV, , BQSTUDIO

Dear TI Experts,

For CEDV gauge, such as BQ78350, we need to set Fixed EDV0, Fixed EDV1,Fixed EDV2 before performing a learning cycle then upload data to GPCCEDV tool.

However, I'm not sure how to set these 3 paremeters , below are 2 methods I heared, could you kindly help to suggest which one is the right choice? Is there another better way to setting Fixed EDVx ? Thanks a lot.

1) Discharge from full to empty with 0.2C, 0.5C, 1C, 5A in room temperature, and calculate the EDVs with 7%, 3%, 0%  of RSOC for each discharge rate, then avarage the result in 4 different discharge rate for EVD0.EDV1,EDV2; Perform 3 cells with above cycle, and do the avarage to decide the final  Fixed EDV0,  Fixed EDV1, Fixed EDV2

2) Discharge from full to empty with actual load with typical user case in actual temperature the pack will be put , and calculate the EDV2,1,0 with 7%, 3%, 0%  of RSOC ; Perform 3 cells with above cycle, and do the avarage to decide the final  Fixed EDV0,  Fixed EDV1, Fixed EDV2

  • Hi Bruce,

    If you are planning to use the GPCCEDV tool and use compensated EDV values, it is not important to identify fixed EDV values first. The GPCCEDV tool needs discharge logs at constant loads and the only data that it uses is: time elapsed, voltage, current, and temperature. You can use the BQ78350 to collect this data for your battery, but it is not required - the important thing is to capture how the battery discharge curve behaves with different loads and temperatures.

    When you capture this data with the BQ78350, you want to make sure there are no protection faults triggered causing the FETs to open and make sure the battery is fully charged and let it rest for 2 hours before staring the discharge to let it reach equilibrium. For accurate temperature measurement, make sure the thermistor is attached to the surface of the cell.

    Here are some notes below on using fixed EDV vs. CEDV (more accurate):

    EDV:

    1.       Set the EDV_CMP = 0 in  CEDV Gauging Configuration and use one of the 2 approaches:

    a.       Rough estimation

    i.      Find the discharge curves for the cell from the manufacturer

    ii.      Pick the capacity at the rate you intend to discharge and the voltage where you intend to stop.  This is the design capacity and the EDV0.

    iii.      Calculate 97% of the capacity and find the voltage on the curve.  This is EDV1

    iv.      Calculate 93% of the capacity and find the voltage on the curve.  This is EDV2

    b.       Better calculation

    i.      Set the battery in the normal operating conditions and let the temperature stabilize.

    ii.       (If you don’t know where you are starting, turn off overcharge protection and set voltage protections to allow full range.)  Charge the pack to full. 

    iii.      Log discharge until you reach the “empty” voltage. If using average cell voltage gauging allow some margin for the CUV threshold in setup so you can reach empty.

    iv.      Calculate discharged capacity by adding the current x incremented time at each log point.

    v.      Select EDV0 voltage where the pack is “empty”, either the manufacturer stated cutoff voltage or some selected value with margin

    vi.      Calculate 97% of the passed charge to the EDV0 point, find the corresponding voltage in the log.  This is EDV1.

    vii.      Calculate 93% of the passed charge to the EDV0 point, find the corresponding voltage in the log.  This is EDV2.

    viii.      Select your design capacity.  You might choose the data sheet capacity or the typical capacity for your discharge rate or some other capacity from your selected log point assuming typical cells.

    2.       Load the values to data memory.

    3.       Run confirmation cycles as desired

    CEDV:

    1.       Set the EDV_CMP = 1 in  CEDV Gauging Configuration

    2.       Run 6 logs:  Normal temperature, high temperature, low temperature, at each termperature run a low current and high current log.

    a.       See http://www.ti.com/tool/gpccedv  available in the bq78350-R1 product folder Tools & software tab software section, and its user guide http://www.ti.com/lit/pdf/sluub45 .

    i.      There is also the http://www.ti.com/tool/gaugeparcal available in the Development tools section of the product folder tab.  If you go to this link it will lead you back to gpccedv.   It can be helpful as a overview of different setups if you are interested.

    b.       Before each discharge log, charge the pack to full.  Turn off overcharge protection and set voltage protections to allow full range (once).  Be sure the temperature sensor is on the cell rather than in the environment.

    3.       Trim any excess data in the logs.  The tool expects to see discharge only, not charge.  Remove charge and long relaxation.  See notes in documents, if any.

    4.       Assemble a zip file

    a.       bqStudio has the “GPCPackager” tab to help enter data and collect the log files

    5.       Submit to the web tool, use “Upload zip file” button at http://www.ti.com/tool/gpccedv

    6.       Review the emailed results for errors

    7.       Load the parameters to the data memory.  The tool produces excess parameters for other CEDV gauges.  The required parameters for the bq78350 are shown below.  Note the order is different, the name can be matched removing the “EDV”:

     

    GPC_CEDV.TXT name

    Bq78350 Data memory name

    EMF

    EMF

    EDVC0

    C0

    EDVC1

    C1

    EDVR1

    R1

    EDVR0

    R0

    EDVT0

    T0

    EDVTC

    TC

    8.       Run confirmation cycles as desired.

    Best regards,

    Matt

  • Dear Matt,
    Thank you so much for your detailed guide of Fix EDV Vs CEDV