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BQ27Z561: Power management forum

Sarth%20Dave
Prodigy 140 points
Part Number: BQ27Z561
Other Parts Discussed in Thread: BQSTUDIO

Hello,

We are executing a learning cycle for our 30Ah battery pack using the BQ27Z561 on board one of our products. Following are the parameters for the battery pack:

  1. No. of cells: 12
  2. Rated capacity of battery pack: 30000 mAh
  3. Rated capacity of single cell: 2500 mAh
  4. Nominal pack voltage: 3.7V
  5. Maximum pack voltage: 4.2V
  6. Charging current (standard): 5A
  7. Charge termination current: <=600 mA
  8. Cut-off voltage: 2.7V

Following are the parameters that we used to execute learning cycle using BQStudio:

  1. Charge term taper current: 300mA
  2. Quit current: 90 mA
  3. Discharge current threshold: 100 mA
  4. Charging current threshold: 100 mA
  5. Charge terminal voltage: 4.1V
  6. Obtained CHEMID using GPC CHEM tool: 0261

With the following parameters written into the BQ27Z561 using BQStudio, we started the learning cycle process following the steps in SLUA903 document. 

The first discharging and relax cycle went fine and were as described in the document. However, when we begin the charging process, the [VOK] bit does not set (which it should automatically, as per the document). Further carrying on with the charging process, the [FC] bit does in fact set after the charging is complete. Moreover, once the relax period is over after the charging, the [REST] bit also sets as it should. but, the LStatus is not updated from "4" to "5". We doubt that the [VOK] bit not setting in the beginning of the charging process might be causing the problem. What are the parameters that control the setting and clearing of the [VOK] bit? We have executed this 2 times with similar result.  Kindly guide us further on how shall we proceed in this matter.

Let us know in case you require more information about our setup. 

Regards,
Sarth

  • 0
    TI__Intellectual 2146 points

    Hi Sarth,

    Do you have a log and a .gg.csv file so we can take a look?

    Can you also confirm that the chemistry report provides an accurate match (< 3%)? Not getting this correct can cause errors in the learning cycle. Are you also discharging to below 10% of RSOC?

  • 0 in reply to Albert Anwar
    Prodigy 140 points

    Hello Albert,

    I am sharing the log file and .gg.csv file here. The chemistry report provided a match with <5% accuracy. I am discharging the battery pack to is rated capacity (i.e 30000 mAh, or till its terminal voltage reaches 2.7V, after this the internal protection circuitry will cut the battery pack off). After the discharging process, both the [FD] and [TD] bits did set. 

    30Ah_LC_Logs.log

    Parameters.gg.csv

  • 0 in reply to Sarth%20Dave
    TI__Intellectual 2146 points

    Sarth,

    It seems like the VOK isn't setting on discharge either, and when you get to relax mode it doesn't trigger a QMax update. Try using the alternate method outlined in SLUA903, with Impedance Track disabled on the first discharge, and see what you get.

  • 0 in reply to Albert Anwar
    Prodigy 140 points

    Thanks for the response Albert,

    I tried the alternate method described in SLUA903 as well. Everything went fine as per the description in the document. However, the QMAX update did not take place with this either. The REST bit was set after the charging and relax cycle but since the QMAX update did not occur, the LStatus did not change from 4 to 5. Any idea why he QMAX update is not taking place even after everything is fine with the process and parameters? I am also attaching the log file for you reference.\

    ThanksLC_Logs.log again!

  • 0 in reply to Sarth%20Dave
    TI__Genius 10370 points

    Sarth,

    Please take a look at the following. If you are unable to move from 04 to 05 update status. Your DOD is most likely not coving the 90% needed for the first update. 

    I reviewed your log. Your DOD is getting capped to 0, meaning you are charging above the chemID max voltage. The gauge doesnt know how to handle this and doesn't allow it to work.  Which chemID are you using? Are you able to charge to a smaller value? 

    Please use the log file you provided and run it through our GPC online tools. i would do both the match and the golden tools with this one log file. 

    Thanks,

    Eric Vos

    Practical_use_of_Single-Cell_Gas_Gauges.pdf