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BQ34Z100-G1: BQ34z100-g1. Charge Termination 2

Gorka Lorea
Expert 1620 points
Part Number: BQ34Z100-G1


Hi,

I wrote a post in the forum 10 days ago but even now questions remain unanswered. This was my previous post.

I am using a BQ34z100-g1 with an 8s2p LiFePO4 batteries. 

I have been finding problems with charge termination because in some cases bq34z100-g1 is not reaching the FC condition. I attach the following image when you can see the differents tests I have done. 

When Current taper window is 60s (2 taper windows would be 120s) and taper current is 40mA, I have never achieved to reach a charge termination. I have tried to reduce the min taper capacity to 0mAh but it is still impossible. 

When current taper window is 60s but taper current is > 70mA, bq34z100-g1 always do a charge termination.

What can be happening with this charge terminations? is there any condition, no specified in the datasheet, to be taken into account?

Thankyou very much in advance,

  • 0
    TI__Mastermind 25955 points
    Hi Gorka,

    Please provide the logs of the event and your gg.csv files for analysis.

    Thank you!

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    TI__Mastermind 25955 points
    Hi Gorka,

    If you're still having the issue, please provide logs of the event, your gg.csv file and your SREC file so we may analyze the tests and settings for your device. The waveform must be analyzed.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Expert 1620 points

    Hi Bryan,

    Here I am with the log of the event. The Taper current is set to 40mA, the min Taper capacity is set to 5mAhr and Taper Voltage is 25mV (where cell charge voltage is 3437mV for a 27496mV total voltage of the 8 cell battery).

    As you can see in the log voltage is higher than (27496- 25x8) and taper current is less than 40mA during more time than 120s. However no charge termination is reached. 

    2210.ChargeTerminationFail_180717.log

    And also with the gg.csv and the srec file

    https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/IED_5F00_P8_5F00_1_5F00_ChargeTermiFail_5F00_180717.7z

    I do not know why I am having these problems with charge termination at these low currents. I do not have problems at higher current so first of all I tought it was due to  Min taper Capacity. I set it at 5mAhr but the problem did not disappear. 

    Thank you very much in advance,

  • 0 in reply to Gorka Lorea
    TI__Mastermind 25955 points
    Hi Gorka,

    Thank you very much for the files. I will provide an update on Monday.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    TI__Mastermind 25955 points
    Hi Gorka,

    The design energy scale is set to 10, with a capacity of 3200. The design energy of the device should be: Design energy = the nominal single cell voltage * design capacity / energy scale, where design capacity = capacity of cell in mAh * # of parallel cells. Please update these values.

    If the issue persists after these changes, please evaluate the cell taper values and ensure they match the information in the datasheet of the battery, as some of these values are no longer the defaults.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Expert 1620 points

    Hi Bryan,

    The LiFePO4 battery  is an 8 cell battery with nominla voltage of 25.6V (3.2V cell nominal voltage) and 3200mAh. So the battery has a capacity of 81.92Wh (one cell: 8192/8 = 1024mWh).

    You mean I have to update Design Energy to the following values?

    Design Energy = 3.2*3200/10 = 1024

    So, design Energy is based on the the energy of one cell, not the complete battery. 

    Why this action can interfere in charge termination?

    Best regards,

  • 0 in reply to Gorka Lorea
    TI__Mastermind 25955 points

    Hi Gorka,

    If each cell of the battery has a capacity of 3200 mAh:

    Design capacity = 3200 * 2 = 6400 mAh
    Design energy = 6400 * 3.2 = 20480 mWh

    design energy scale = 1


    The design capacity and design energy values are used when the compensated battery capacity remaining and capacity when fully charged calculations are performed by the bq34z100-G1. They are also used in some load mode/selects.

    Sincerely,
    Bryan Kahler

  • 0 in reply to Bryan Kahler
    Expert 1620 points

    Hi Bryan,

    I think you did not understand me perhaps because my explanations were not clear at all.  

    The LiFePO4 battery is composed by 8 cells in series. (no rows in pararell). The capacity of each cell is 3200mAh. The total energy of the battery is 25.6*3200 = 81920mWh.

    If we take cell values the designa capacity should be 3200mAh and the design energy should be 3200mAh*3.2 = 1024mWh

    So, why is design capacity 6400 mAh? why is design energy 20480 mWh?

     

    Best regards,

  • 0 in reply to Gorka Lorea
    TI__Mastermind 25955 points
    Hi Gorka,

    Thank you for the clarification! From the original post I read, "I am using a BQ34z100-g1 with an 8s2p LiFePO4 batteries".

    This is where I was getting the figure for 16 cells total, 8 in series, 2 in parallel.

    To confirm, the pack is 8s1p consisting of 8 cells in total where each cell has a capacity of 3200 mAh and a nominal voltage of 3.2 V?

    If that is the case, please modify the instructions from above to be thus:

    Design capacity = 3200 * 1 = 3200 mAh
    Design energy = 3200 * 3.2 = 10240 mWh

    design energy scale = 1

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Expert 1620 points

    Hi Bryan,

    Sorry for my late reply, I have been on holidays the past 2 weeks.

    I have tried to do a charge termination with the changes you suggested me but it did not work.  

    I attach log of the charge termination and also the gg.csv with the new parameters (design energy scale and design energy)

    8S2P_180820.rar

    If this did not work, what can be the cause os these fail charge terminations?

  • 0 in reply to Gorka Lorea
    TI__Mastermind 25955 points
    Hi Gorka,

    Please calibrate your gauge for current.

    The CC Gain is 790 mOhm while the CC Delta is 10.147 mOhm. These values usually should be very similiar.

    The 790 value is most likely causing the failure.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Expert 1620 points

    Hi Bryan,

    Thank you very much for your answer.

    What do these parameters exactly mean?

  • 0 in reply to Gorka Lorea
    TI__Mastermind 25955 points
    Hi Gorka,

    CC Gain is the gain factor for calibrating Sense Resistor, Trace, and internal Coulomb Counter (integrating ADC delta sigma) errors. It is used in the algorithm that reports Average Current.

    CC Delta is the gain factor for calibrating Sense Resistor, Trace, and internal Coulomb Counter (integrating ADC delta sigma) errors. It is used in the algorithm that reports charge and discharge in and out of the battery through the Remaining Capacity register.

    The difference between CC Gain and CC Delta is that the algorithm that reports Average Current cancels out the time base because Average Current does not have a time component (it reports in mA) and CC Delta requires a time base for reporting Remaining Capacity (it reports in mAh).

    CC Gain and CC Delta do not need to be modified directly by the user. They are modified by the current calibration function from Calibration mode.

    Sincerely,
    Bryan Kahler