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BQ27421EVM-G1A: RES_UP and RUP_DIS are set at the same time during learning cycle discharge

Yonglan Ye
Prodigy 70 points
Part Number: BQ27421EVM-G1A
Other Parts Discussed in Thread: GPCCHEM

Hi,

I am currently using bq27421-G1A for my thesis design, I have encountered a problem during learning cycles.

The battery I am using is a 150mAh 4.2V LiCoO2-based rechargeable battery.

So I have no problem getting an Qmax update but during the last discharge cycle, where the resistance table is supposed to be updated, RES_UP and RUP_DIS are set at the same time. The battery is discharged at about -20mA, which is about C/7.5. 

I am currently thinking about two possibilities:

  1. The battery chemistry does not match the gauge IC's pre-programmed profile;
  2. The discharge current is too small for a battery with small design capacity. I saw in another post that someone had the problem of getting RES_UP to set when they performed a learning cycle on a 300mAh battery, and they solved the problem by increasing discharge current to C/3. However, in my case, RES_UP can be set but just the RUP_DIS is set at the same time.

Could anyone shed some light on this and give me some guidance on how I can proceed?

Regards,

Kaylee

  • 0
    TI__Guru* 76230 points
    Hi Kaylee,
    What does your update status say after the learning completes? It is possible your update status has changed meaning learning cycle was successful even though rup dis got set. Your update status ought to have gone from 02 to 00 during learning.

    Also, Did you check to see if the default chem ids are a match for your cells using gpcchem?
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 70 points
    Hi Onyx,

    I did not manage to finish the learning cycle because of lost of connection to the battery. I only got to deplete the battery to around 20%. The Update Status still remained zero at that point. Would it only change from 00 to 02 by the time it completes all grid point updates?

    What's more interesting is the Ra table did get updated to half of its default values by the time SOC hits around 85%. From that point on, the Ra table had not been updated.

    I have not checked the default chem ids yet. I will do it as soon as possible. I am current trying to use the GDK to discharge the battery faster, at C/3. I'm not sure if it has something to do with the small capacity of the battery (150mAh). But I am guessing the OCV-cell_voltage may be too small to be observed if current is not significant.

    Please let me know what you think.

    Thank you,

    Kaylee
  • 0 in reply to Onyx Ahiakwo
    Prodigy 70 points

    Hi Onyx,

    So I did the learning cycle again yesterday with a discharge rate of C/3 and charge at C. It has the same behavior as last time, once [RES_UP] is set, [RUP_DIS] is set as well. This happened when SOC dropped to 92%. All 15 values in the Ra table got updated and became half of the default values. No more updates after that. 

    Even when the whole learning cycle is completed, UPDATE_STATUS remains unchanged, which is still 00. 

    I have attached the log file with the final gg file. I really appreciate your help.

    Thank you,

    Kaylee

    learningCycles.zip

  • 0 in reply to Yonglan Ye
    TI__Guru* 76230 points
    Hi Kaylee,
    You need to set update status to 02 before you start a learning cycle. Once learning completes update status will be 0.

    For learning,
    -perform a soft reset.
    -discharge to empty using c/7
    -rest 5 hours.
    -charge to full
    -rest 2 hours
    -discharge to empty
    -rest 5 hours.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 70 points
    Hi Onyx,

    I thought update status would only change to 02 when it finishes a learning cycle. Do I need to manually set update status?

    Thanks,

    Kaylee
  • 0 in reply to Yonglan Ye
    TI__Guru* 76230 points
    Hi Kaylee,
    No update status on this gauge goes from 02 to 00. You have to set it to 02 before you start the learning cycle. At the end of the learning cycle, update status will be 00

    thanks
    Onyx