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BQ27510-G3: At the end of discharge, TTE decrease slowly

Stephane JUHEL
Intellectual 320 points
Part Number: BQ27510-G3

Hello,

After performing the golden image, i check the SOC and the TTE on the product

Every 10 sec, I read the TTE and SOC.

During the discharge, the TTE is acceptable and follow a straight line during 8 hours. The TTE decrease every minute. It is OK

But for the last 5 minutes the TTE decrease very slowly.

TTE = 5 during 1min30sec

TTE = 4 during 1min30sec

TTE = 3 during 2min0sec

TTE = 2 during 4min10sec

TTE = 1 during 6min20sec

Please find curve for the voltage, current, TTE and SOC during charge and discharge

Please find the log during the last 5 minutes

13/09/2018 20:03
Temp Voltage FCC Current TTE_Coef_1 Cycles SOC
315 3392 7062 -853 5 14 2                TTE = 5 during 1min30sec
315 3392 7062 -853 5 14 2
315 3391 7062 -853 5 14 2
315 3391 7062 -853 5 14 2
315 3390 7062 -853 5 14 1
315 3390 7062 -853 5 14 1
315 3390 7062 -853 5 14 1
315 3390 7062 -853 5 14 1
315 3390 7062 -854 5 14 1
315 3390 7062 -854 4 14 1                TTE = 4 during 1min30sec
315 3389 7062 -854 4 14 1
315 3389 7062 -854 4 14 1
315 3389 7062 -854 4 14 1
315 3388 7062 -854 4 14 1
315 3387 7062 -854 4 14 1
315 3388 7062 -854 4 14 1
315 3387 7062 -854 4 14 1
315 3387 7062 -854 4 14 1
315 3387 7062 -854 3 14 1                TTE = 3 during 2min0sec
315 3386 7062 -854 3 14 1
315 3386 7062 -855 3 14 1
315 3386 7062 -855 3 14 1
315 3385 7062 -855 3 14 1
315 3385 7062 -855 3 14 1
315 3384 7062 -855 3 14 1
315 3384 7062 -855 3 14 1
315 3384 7062 -855 3 14 1
315 3383 7062 -855 3 14 1
315 3383 7062 -855 3 14 1
315 3382 7062 -855 3 14 1
315 3382 7062 -855 2 14 1                TTE = 2 during 4min10sec
315 3382 7062 -855 2 14 1
315 3381 7062 -856 2 14 1
315 3381 7062 -856 2 14 1
315 3381 7062 -856 2 14 1
315 3380 7062 -856 2 14 1
315 3379 7062 -856 2 14 1
315 3379 7062 -856 2 14 1
315 3378 7062 -856 2 14 1
315 3378 7062 -856 2 14 1
315 3378 7062 -857 2 14 1
315 3377 7062 -857 2 14 1
315 3376 7062 -857 2 14 1
315 3377 7062 -857 2 14 1
315 3375 7062 -857 2 14 1
315 3375 7062 -857 2 14 1
315 3375 7062 -857 2 14 1
315 3374 7062 -857 2 14 1
315 3368 7062 -905 2 14 1
315 3373 7062 -857 2 14 1
315 3372 7062 -858 2 14 1
315 3372 7062 -858 2 14 1
315 3371 7062 -858 2 14 1
315 3370 7062 -858 2 14 1
315 3369 7062 -858 2 14 1
315 3369 7062 -858 1 14 1                TTE = 1 during 6min20sec
315 3369 7062 -859 1 14 1
315 3368 7062 -858 1 14 1
315 3367 7062 -859 1 14 1
315 3366 7062 -859 1 14 1
315 3366 7062 -899 1 14 1
315 3365 7062 -860 1 14 1
315 3364 7062 -860 1 14 1
315 3363 7062 -860 1 14 1
315 3362 7062 -861 1 14 1
315 3361 7062 -861 1 14 1
315 3361 7062 -861 1 14 1
315 3359 7062 -861 1 14 1
315 3358 7062 -861 1 14 1
315 3357 7062 -861 1 14 1
315 3357 7062 -861 1 14 1
315 3356 7062 -862 1 14 1
315 3355 7062 -862 1 14 1
315 3354 7062 -863 1 14 1
315 3353 7062 -863 1 14 1
315 3352 7062 -863 1 14 1
315 3351 7062 -863 1 14 1
315 3350 7062 -864 1 14 1
315 3348 7062 -864 1 14 1
315 3347 7062 -864 1 14 1
315 3346 7062 -864 1 14 1
315 3345 7062 -865 1 14 1
315 3344 7062 -864 1 14 1
315 3342 7062 -865 1 14 1
316 3341 7062 -865 1 14 1
315 3340 7062 -866 1 14 1
315 3338 7062 -867 1 14 1
316 3337 7062 -867 1 14 1
316 3336 7062 -868 1 14 1
316 3334 7062 -867 1 14 1
316 3333 7062 -868 1 14 1
316 3332 7062 -868 1 14 1
316 3330 7062 -869 1 14 1
316 3330 7062 -859 0 14 1
316 3328 7062 -860 0 14 1

What are the parameters to adjust to have a TTE that decreases correctly if it is possible ?

It is possible to do better ? If yes how ?

Thanks and Best Regard

Stéphane

  • 0 in reply to Stephane JUHEL
    TI__Mastermind 24870 points
    Hello Stephane,

    Can you please attach the log file as an attachment?
  • 0 in reply to Kang Kang
    Intellectual 320 points

    Dear Kang,

    Please find the log in a excel file for a complete charge then a complete discharge.

    We charge the battery only at 4.1V.

    Please find also the golden image if you can see something wrong.

    Thanks and best regards

    Stéphane0510_4_00-bq27510G3_20180726.zip2022.15G00030 - Forum Texas.xlsx

  • 0 in reply to Stephane JUHEL
    TI__Mastermind 24870 points
    Hello Stephane,

    You have a few additional columns and I wanted to clarify these.

    The log file shows approximately 9 hours of physical discharge. (8:53:10 for a duration).

    What is the accuracy you are expecting. I see that you are calculating time to empty (ideal) in column M assuming a constant current discharge. However, I looked at the State of Charge Accuracy assuming your system shuts down at near 3300 mV and this seems to be quite good.

    I looked at the graphs page and saw that the state of charge moves between your ideal lines, but I think the "ideal" line is calculated from a fixed time and fixed current.

    I calculated accuracy using the following method: e2e.ti.com/.../how-accurate-is-your-battery-fuel-gauge-part-2-2

    Our TTE is calculated based on internal adjustments, we could potentially perform better, but my recommendation is to use a constant current experiment if your "ideal" TTE is performed using a constant current assumption.

    Thanks
  • 0 in reply to Kang Kang
    Intellectual 320 points

    Hello,

    About the additional columns, it is an ideal autonomy with a TTE decreasing along a straight line (ideal 8h30 ideal 9h ...)

    Then I check that the real TTE curve is parallel to an ideal TTE line.

    The ideal TTE are made to compare the real TTE but not the SOC

    For the first 8 hours of discharge, it is acceptable. TTE from around 540 to 10 minutes

    For TTE from 10 to 1 minute, the curve does not follow an ideal line

    When we do the Learning cycle, we perform with an electronic charge at 1A. (constant current during all the discharge)

    I performe the Learning cycle at 4.2V. On the final product the charging voltage is 4.1V. When i generate the golden image, i change charging voltage : 4.2V-->4.1, and the design capacity (93% of the capacity at 4.2V)

    But on the final product, the charge is not a constant courant discharge but a power constant discharge (current around 730mA at 4030mv and a current around 860mA at 3350mV)

    On the final product, we display the remaining battery autonomy in hours minutes. We don't display the SOC in %.

    When the displayed autonomy TTE is 10min, I expect it takes only 10 minutes to go from a TTE of 10min to 0 and not 20 minutes.

    Do you think, I can have better results for the last 10 minutes ? If Yes, what are the parameters to adjust ?

    Do you have some documentation and recommendation when the charging voltage is 4.1V ? How to perform Learning cycle and generate golden image for a system at 4.1V ?

    When we are in working mode, how can we be sure that the gauge adjusts as the cycles and aging of the battery progress ?

    Thanks for your help

    Stéphane

  • 0 in reply to Stephane JUHEL
    TI__Guru* 76230 points
    the learning cycle is the same for a 4.2V system and a 4.1V system. When charging to full during the learn cycle, it has to be charged to 4.2V. After learning has completed, you can adjust your charger to charge to 4.1V and make sure to taper such that the gauge sets the FC flag. The gauge will then adjust the FCC to reflect the 4.1V.

    The gauge will update the qmax and resistance tables as the battery ages. This ensures you maintain high sOC accuracy.

    TTE is not really something that can be predicted accurately if your current is not constant.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 320 points
    Dear Onyx and Kang.
    I did a new learning cycle and it is OK. I change the terminate voltage at 3000mV during the learning instead of 3150mV, then i adjust the terminate voltage at 3200mV in the golden image for the final product.
    Thanks
    Stéphane