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bq40z60 charging stops/current decreases

Nermin H.
Prodigy 190 points
Other Parts Discussed in Thread: BQ40Z60EVM-578, BQSTUDIO

Hi,

I am using the "bq40z60evm-578" board for charging four Li-Ion (3,7V/2600mAh) batteries (4s). I'm using bqstudio with the default settings except for the cell count and the capacitiy values. For charging I use an AC adapter which provides 19V/4,7A.

When I monitor the current using the data graph in bqstudio i notice that the charging process stops every few seconds and starts again afterwards - you can see this behaviour in the attached image. Furthermore i noticed that the current decreases while charging - after 90% the gauge respectively the graph shows less than 80mA. (see ) I checked the ac adapter during charging and it looks fine - the system is supplied with voltage all the time.

I've also kept an eye on the temperature data and I noticed that after the temperature exceeds 31°C the current jumps to 0A. Otherwise if the temperature falls below 29°C the current increases again. ( )

Did I forget to change some important settings ? Where can I find a sample .gg.csv-File which suits my components to give it a try ?


Nermin

Data Graphs.pdf

datalog.log

  • 0
    TI__Guru 73830 points

    Nermin, 

    Please review the Charger Setup section (pg 58) of the TRM. The Minimum Output Voltage and Voltage Resolution need to be updated when changing the number of series cells. R1 is the lower resistor and R2 is the top resistor in the feedback ladder in these equations. Also, make sure that your charger can support the charging current in the data flash.


    Tom

  • 0 in reply to ThomasCosby
    Prodigy 190 points
    Hi Tom,

    Thank you very much for your quick reply.

    I have now updated the values for Maximum Voltage Output and Voltage Resolution. I have also made sure that the jumper is set correctly for the 4S application. The charging process does not stop anymore and i got my batteries charged up to 100%.

    But i still don't understand the effect of the chip temperature on the charging process - like I mentioned before the current decreases after exceeding a chip temperature of 31°C. Is this value defined somewhere in the settings? I have set the values for the current in the "High Temp Charging"-section all to 2000mA. Is this temperature threshold of 31°C a result of the settings in "Temperature Ranges" (T1-T6) or where does it come from?

    Regards,
    Nermin
  • 0 in reply to Nermin H.
    TI__Guru 73830 points
    The High Temp Charging current parameters should set the current in that case. Have you checked the "Charging Current" on the Registers screen to see what current the gauge is requesting?
  • 0 in reply to ThomasCosby
    Prodigy 190 points
    I have done a new measurement starting at 59% relative State of Charge and recorded the "Current" and the "Charging Current" you've mentioned - i have attached the logfile respectively the .pdf with the recorded data graphs. Before the measurement i have set all "Temp Charging" values as default which means my "High Temp Charging" settings look like this:

    Voltage = 4000 mV
    Current Low = 1012 mA
    Current Med = 1980 mA
    Current High = 1496 mA

    and the Standard Temp Charging look like this:

    Voltage = 4200 mV
    Current Low = 1980 mA
    Current Med = 2000 mA
    Current High = 2000 mA

    Based on the attached files you can see that the Current value roughly follows the Charging Current value. As soon as the chip temperature exceeds 31°C Charging Current goes down to 1980 mA and above 33°C it down to 1496 mA. Until 63% relative State of Charge the Current value matches almost the Charging Current value all the time. After that the Current decreases slowly as the relative State of Charge is approaching 100%. At about 97% the current jumps down by approximately 150 mA.

    Is this a common and reasonable behaviour ?
  • 0 in reply to Nermin H.
    TI__Guru 73830 points
    Nermin,
    I did not receive the .pdf files. You can select the "Use rich formatting" text on the reply window and then drag the file into the window to attach it to the posting.
    Tom
  • 0 in reply to ThomasCosby
    Prodigy 190 points

    Tom,

    I obviously added the files to my first post. I'm sorry - here are the files one more time.

    4111.Data Graphs.pdf

    5277.datalog.log

     

  • 0 in reply to Nermin H.
    TI__Guru 73830 points

    Nermin,

    The log data does not show the pack voltage, but the current looks normal. The current will taper as the pack voltage approaches the charging voltage. The temperature observations appear to just be coincidence.

    Tom

  • 0 in reply to ThomasCosby
    Prodigy 190 points
    Thank you very much for your help, Tom. I appreciate it!

    Regards,
    Nermin