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Original question:

BQ78350-R1: Charging issues

BQ78350-R1: What is procedure to get accurate soc?

vinay kambappa
Prodigy 160 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQSTUDIO, BQ78350, BQ40Z50-R1, BQ40Z50, , GPCCEDV

Hi,

I have found the exact cell Chem Id on the bqstudio tool still I don't get the accurate SOC. Now I want to know the procedure to be followed to get accurate SOC of battery pack? I have gone through the documentation available at the website ie CEDV parameter calculations and learning cycle. I am confused about which needs to be done first, should we calculate the cedv coefficients first by logging 6 files, or the learning cycle? Also what are the values need to be configured(current parameter, voltage parameter )before doing the CEDV logging (6 files). 

Currently I have calibrated the current , changed the cell temperature coefficients as per the thermistor. 

Thanks,

Vinay kambappa

  • 0
    TI__Guru* 81034 points

    Hi Vinay,

    The ChemID is only used to estimate the initial SOC immediately after power-up or after a Reset on the BQ78350. After that point, it will use coulomb counting to track the SOC and the accuracy will depend on the CEDV parameters.

    The 6 log files do not depend so much on the gauge settings. You can characterize the battery without using the BQ78350. You just need to capture the voltage, current, and temperature during a discharge. After you collect the 6 log files, you need to program the CEDV parameters to the BQ78350. You also need to program the other key gauging parameters like the Design Capacity, the Learned Full Charge Capacity (set this equal to the Design Capacity to start), the AFE Cell Map, set the [EDV_CMP] bit in the CEDV Gauging Configuration register. You should go through all of the gauging and protection settings to make sure they are set according to your application needs.

    If your pack is 4S, is there a reason you are using the BQ78350-R1 instead of the BQ40Z50 gauge. The BQ40Z50-R1 fully integrates the gauging and protection into one device. This video is very helpful for setting up the BQ40Z50 which is an Impedance Track gauge (uses ChemID, but does not use CEDV): https://training.ti.com/bq40z50-setup-and-going-production 

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 160 points

    Thank you, I will enable the EDV_CMP bit, set the designed capacity and FCC before logging the discharge data.

    What happens if we don't set the EDV_CMP bit before logging and use these logged files to generate coefficients? Because I have a 2 pairs of  logged files(at 2 different temperature) in which EDV_CMP was not set. Can I use these files to generate Coefficients.

     

    Above is the Screenshot of the Current SOC indicated on Bqstudio.

  • +1 in reply to vinay kambappa
    TI__Guru* 81034 points

    The EDV_CMP bit is not important for collecting the logs. The important information from the logs is the voltage, current, and temperature. The GPCCEDV tool will recommend CEDV parameters based on your settings. After you have finished this process, then you can set the EDV_CMP bit and program your CEDV parameters to the gauge.