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BQ76940: ambient temperature setting for of CEDV gas gauge calibration

prasanna dhayalan
Prodigy 30 points
Part Number: BQ76940
Other Parts Discussed in Thread: GPCCEDV

I am trying to  calibrate gas gauge for SOC estimation of my LI-ion battery pack, based on CEDV calibration document the temperature range proposed are as follows: 0 to5 deg C, 25 to 30 deg C, 40 to 50 deg C.

My BMS setup: AFE - BQ7694003 GG ASIC : BQ78350DBTR-R1

on my application, the battery is expected to discharge between -20deg C until 60 deg C.

1) Will it be possible to log from -20deg C? Can the GG properly map at this ambient temperature.?

2) How many temperature points are need to be log? should it be one or multiple? --> If one then what should be this test point , whether the hottest cell(hotspot) location in the pack?

  • 0
    TI__Guru* 81035 points

    Hi Prasanna,

    It is best to use the recommended temperatures to generate the CEDV parameters in this case. One temperature per log file is what is expected by the GPCCEDV tool (3 temperatures and 2 current loads for a total of 6 log files). These recommended temperatures are more likely to generate optimum parameters. The CEDV parameters you generate will extrapolate to lower and higher temperatures, so gauging will still work from -20C to 60C.

    The problem with using a log file at -20C is the very low temperature will pull the cell voltages very low and greatly reduce the capacity. This log file will be a poor mathematical predictor for the other temperatures. In the application, you may want to consider limiting the discharge at very low temperatures in order to get more life out of the battery. This temperature may reduce the effective capacity by 50% or more. 

    The test point should be on one of the cells and the same measurement point should be used for each log file.

    Best regards,

    Matt