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BQ4050: BQ4050 "selfdischarge rate" function Test

zhao xinghui
Prodigy 20 points
Part Number: BQ4050
Other Parts Discussed in Thread: BQSTUDIO, EV2400

HI 

  • I'm testing the "SelfDischarge" function. There is a problem,"Ignore_sd" is set 0,"selfdischarge rate" 0.2%/day.The battery pack was left for a week at room temperature, but there was no change in SOC.  CEDV RC is reduced, at this time I cancel the smooth function,  the SOC will be reduced (reduced to CEDV RC), why does the SOC remain unchanged after standing for a week under the smooth function.Or what should i do to use "selfdischarge"  to reduce SOC in "smooth" .  

  • 0
    TI__Guru** 105590 points

    Hello Zhao,

    What exactly are you changing in the registers to disable smoothing? Smoothing is most likely not needed for the application, when smoothing is enabled the gauge will add extra charge so the RemCap is at SOC = 0% or 100% (depending on the smoothing) at the terminate voltage or charge termination. It uses the slope of the voltage to determine how much charge to add.

    Smoothing may be preventing the RemCap since the slope of the voltage is basically non-existent at rest, so it will not allow changes in the charge.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 20 points

    What I want is for the battery pack to sit for a long time with "SMEN=1" , the SOC will decrease as I set the “self-discharge rate”.  The current testing phenomenon is that neither RC nor SOC drops when SMEN=1  IGNORE_SD=0 (but CEDV RC does).  RC and SOC drop only when SMEN=0.  

  • 0 in reply to zhao xinghui
    TI__Guru** 105590 points

    Hello Zhao,

    Smoothing may be preventing the change in SOC as I mentioned above.

    Can you share a screenshot of your register dashboard using EV2400 and BQStudio? Can you see if the smoothing is active or not during your test?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 20 points

    SMEN=1,IGNORE_SD=0Hello Keller，

    As shown in the BQStudio screenshot,smoothing is active.If I need to use both "smooth" and "selfdischarge"  , what should I do? 

    Batt said that we can reset the bit IGNORE_SD to use both functions, but the actual test did not .is that true?

  • 0 in reply to zhao xinghui
    TI__Guru** 105590 points

    Hello Zhao,

    Can you send the link for the thread that was screenshotted?

    From reviewing the code I can see there could be a possible way that the smooth will disable self discharge. Can you share the logs you captured during testing showing the CEDV RC decreasing with smoothing enabled and smooth disabled.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 20 points

    Hello Keller

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/826480/bq4050-soc

    This is the link for thethread

    Selfdischarge-smooth.log

    This is the log file with “SMEN=1”, you can see CEDV RC decreased from 4500 to 4541, but the RC did not change（still 4500）.

    Selfdischarge-No-smooth.log

    But when i set "SMEN=0",RC will immediately become 4541.  From the log file,we can see RC and CEDV RC decreased simultaneously(4541-4532)

    2022-05-24.gg.csvThis is my gg file

    Best Wishes，

  • 0 in reply to zhao xinghui
    TI__Guru** 105590 points

    Hello Zhao,

    After looking into this more thoroughly it appears the smoothing functionality does not account for self discharge. If you would like to adjust for self discharge the smoothing feature should be disabled. I will correct the other post by Batt to indicate this.

    Essentially with the smoothing enabled we use a different charge accumulation register (all internal registers, not visible) that does not have the self discharge added. When Smoothing is enabled the gauge switches to use the smoothed accumulation value at all times so the self discharge is effectively bypassed (which is why you see the behavior in the logs, when smoothing is activated it is synced to CEDV RC, when smoothing is disabled the SBS RC() switches to the other accumulation registers which does account for self discharge). This was most likely part of the specification of this firmware, it is just not outlined well in the documentation.

    Sincerely,

    Wyatt Keller