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RSOC dropping to zero immediately during discharge

Patrick Mendiuk
Intellectual 535 points
Other Parts Discussed in Thread: BQ78PL116, BQWIZARD

Hello,

I am working with the bq78pl116 and am experiencing issues with RSOC dropping to zero immediately at the beginning of a discharge. 

With a fresh set of cells I connected to the bq78pl116 via BQWizard without any issues.  I setup the TMAP file for 4 series cells and select chem type 100.  I then calibrated the temp and current successfully.  I then setup the various charge and pack parameters within BQWizard.  I then issue the Learn/Reinit command within BQWizard and commence charging the pack at 0.2C.  With polling turned on I can see the pack charging and the RSOC increasing as expected.  The  Fully Charged bit is set, pack passed current is approx. 10Ah and RSOC indicated 100%.  All seems good.  I let the pack rest for at least 2 hours to allow the pack to get into relaxation mode and update.   I then start a discharge at 0.5C and the RSOC immediately drops to zero.  If i stop the discharge and issue the Learn/Reinit command and restart the discharge the RSOC jumps back up to 100% and updates normally during the discharge period.  I have been through several charge/discharge cycles with identical behaviour. 

Any help would be greatly appreciated.

Thanks very much,

Patrick

  • 0 in reply to Patrick Mendiuk
    TI__Intellectual 1505 points

    Hi Patrick,

    I will need a few questions answered to help trouble shoot your issue.

    1) What type of chemistry are you using and is the cemID 100 the best match for your chemistry?

    2) Did you run an aux file generation to initialize the Gas Gauge? The aux file generation characterizes the cells and pack and ensure that the gass gauge is initilized with the correct Qmax and Resistance values for correct update of the gg.

    3) could you send out a copy of your ppcsv file?

    4) generate a pack summary file that will contain all the pertainent gas gauge information for analysis.

    Regards,

    Ben

  • 0 in reply to Benjamin Sarpong
    Intellectual 535 points

    Ben,

    I posted the files you had requested.  

    I selected the default LiCoO2 ChemID 100 because there was no suitable chem file for the LiCoO2 cell I am using.  I included the data sheet for the cell in the zip file.

    I had a pack that had been through a few charge/discharge cycles that appeared to be operating normally but after completing a full charge, the RSOC is now indicating 0% although the BQ78PL116 is reporting QRem(~9600mAh) and QMax(~9800mAh) values for each cell.  Those values agree with the amount of current flow during the charge cycle and with the design capacity(10000mAh).  The RSOC state of charge increased consistently during the charge and remained at 100% for several hours after the charge.  Remaining Capacity was around 9600mAh when the charge terminated but jumped to 10000mAh within a few minutes of charge termination.  Unlike the previous occurrences this pack did not have any discharge current flow after charge completion which caused RSOC to drop to zero.  The only current flow was the BQ78PL116 supply current.

     

    Thanks very much for your help

     

    Patrick

  • 0 in reply to Patrick Mendiuk
    Intellectual 535 points

    Ben,

    I have some additional information.  The pack I mentioned in the previous post updated the RSOC register after I initiated a discharge cycle.  Is there a timer or some other process that clears the RSOC register or is BQWizard possibly creating this condition?

    Thanks for your help

    Patrick

  • 0 in reply to Patrick Mendiuk
    TI__Intellectual 1505 points

    Hi Patrick,

    I had to analyze the data  you had sent. I think the issue is that you have the wrong chemistry ID . The chemID 100  represents an 18650 2.2Ah cell.  Your cells are 10Ah batteries. These are 10x of the chemistry you picked and hence the OCV vs SOC tables represented in this chemID file will not match your chemistry and cell type.

    The RSOC updated from the OCV vs SOC table at the relaxation voltage of your cells ~ 3.7V matches to 0% DOD. and hence when you start discharge, the RSOC will report 0%.

    The way to resolve this issue id to run bqEasy (www.ti.com.cn/cn/lit/ug/sluu278/sluu278.pdf) to find a chemistry that is closet to yours or send a cell to us here in Dallas and we will characterize and release the chemID (this process takes about 4-6wks) 

    Chem ID of: 410  is 10A/h cell with a 3.65V  nominal voltage. This might be an appropiate initial match.,

    Regards,

    Ben