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Gauging Parameter Calculator / config file

Simon Ferres
Prodigy 90 points
Other Parts Discussed in Thread: BQ78350-R1, BQSTUDIO, BQ78350, GPCCEDV

Hi everybody,

Because your mail address 'gpc_support@list.ti.com' doesn't work, I try it this way. We are develobing a battery pack and I'm using BQ78350-R1 as gas gauging IC. For the online tool "gauging parameter calculator" I need to measure different values of the new battery pack and put them together in different files. I have some questions about the configuration file: What does the parameters FitMinSOC%, FitMaxSOC% and LearnSOC% mean. Where do I get these.

Is the 'CellTermV' the 'terminated DISCHARGE voltage' of a cell?

This ducument http://www.ti.com/lit/ug/sluub45a/sluub45a.pdf doesn't explain these parameters.

Best regards.

  • 0
    TI__Guru 73830 points
    The FitMinSOC%, FitMaxSOC% and LearnSOC% set the target SOC for EDV2 and the window for the simulation to try to hit that target. We recommend using the default values for these parameters. The CellTermV is the voltage at the end of discharge where EDV0 should = 0%.
  • 0 in reply to ThomasCosby
    Intellectual 455 points

    I noticed that in the 'Simple Guide to CEDV Data Collection for Gauging Parameter Calculator (GPC)' documentation the defaults are different than the defaults  seen in the GPC packager in bqStudio.

    Documentation:

    FitMaxSOC% = <Typical is 12>
    FitMinSOC% = <Typical is 6>
    LearnSOC% = <Typical is 7>

    bqStudio defaults:

    Top SOC % interval to fit  =       <Default is 9>
    Bottom SOC % interval to fit  = <Default is 3>
    SOC % where FCC learned = <Default is 7>

    Which set of parameters would be recommended?

  • 0 in reply to JOSHUA ANDERSON
    TI__Guru 73830 points
    The SOC% where FCC is learned should always be left at 7%. We recommend using the 3% to 9% range for the other parameters as default values for the simulation and move them to 6% to 12% or 3% to 12%, if required to get the program to create a good set of CEDV coefficients.
  • 0 in reply to ThomasCosby
    Intellectual 365 points

    Hi Thomas,

    Why should EDV2 be set to 7% (bq78350)?

    In my battery usage I don't get below 35%, if the BMS is set to EDV2 at 7% the SoH is never updated, I have to set EDV2 to 50% to get it to update FCC.

    My question is, what should be the following values in my Config.txt for the GPC?

    FitMaxSOC%=?
    FitMinSOC%=?
    LearnSOC%=50

    Thx,

    Yoav

  • 0 in reply to Yoav Gross
    Expert 2475 points
    EDV2 needs to be set to a percentage below the "knee" of the discharge curve and high enough to allow adequate capacity to support the system before EDV0. Setting EDV2 to 7% was chosen, because it should be below the "knee" from most cells. The simulation may not be able to support EDV2 set points in the flat region of the discharge curve above the "knee". Is it possible for you to run a deeper discharge periodically to allow the FCC update with EDV2 set to 7%?
  • 0 in reply to TEC
    Intellectual 365 points

    Hi, I understand that, however it is not practical for me to do a full discharge every x cycles.

    I am using EDV2 set to 50% with CEDV = 0. it is working quite well, as long as the discharge rate is as expected.

    I would like to set CEDV = 1, to have compensation for different currents - to have better accuracy.

    My only question is what should be the values of FitMaxSOC% and FitMinSOC% when LearnSOC%=50? What is the meaning of those parameters?

    Thx,

    Yoav

  • 0 in reply to Yoav Gross
    Expert 2475 points

    FitMaxSOC% and FitMinSOC% is used by the GPCCEDV tool to set the window where the simulation tries to converge on the LearnSOC% point (EDV2). I do not have any experience with trying to set the simulation to run in the flat region, so I would set it to 55% and 50% respectively to see how that works. The curve will be shallow at that point, so I am not sure how accurate the Pending EDV will be. You have been using the FIxed EDV technique, which does not use the firmware simulator.

  • 0 in reply to TEC
    Intellectual 365 points

    I tried sending GPC parameters with several values in FitMaxSOC% and FitMinSOC%, but could not get any reasonable results for setting EDV2 at 50% SOC.

    I can see every 1A causes the pack to drop by 14mV, I am using 6S so its 2.3mV per cell.

    I want parameters that will take the battery OCV at 50% (~3.8V) and reduce (I * 0.0023) to match the Voltage readings.

    Can I have the formula of the CEDV parameters?

    What I found so far is:

    EDV0,1,2 = n (EMF • FBL - | ILOAD | • R0 • FTZ)
    EMF -> no load voltage
    FBL = f ( C0, C + C1, T ) - correction for temperature?
    FTZ = f ( R1 , T0, T, C + C1, TC) - resistance of cells

    I want to understand the two functions for FBL and FTZ.

    Thx