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BQ20Z65 - wrong calculation of FCC and SOC

 

I'm using the BQ20Z65 with a 4s6p pack. Since short time we are delivering battery packs with this configuration. Today I got some returns from a customer with the fault that the SOC is wrong. They were charging the batteries, but SOC was still at 30 % even the batteries were fully charged. When they arrived, SOC showed 100 % and FCC was in a range of 7800 mAH, but the battery should have 9000 mAh. When applying a load to the battery the FCC changed to 2700 mAH, SOC ist still at 100 %. When charging the battery, SOC stays at 2700 mAH.

What goes wrong with the calculations? Can you please help me?

 

Michael Houzer

 

  • Michael,

    Have you chosen the correct chemistry ID for the specific batteries you are using? This is done using bqEasy, and is detailed in Section 4 of slua421a, which is linked below.

    http://focus.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=slua421a&fileType=pdf

    It sounds like the issue might be that the chem ID is incorrect, which causes problems for the Impedance Track algorithm, and could be creating the errors that you are seeing.

    Regards,

    Jason

  •  

    Jason,

    thank you for your answer. I'm shure I selected the chemistry before doing the two charge/discharge cycles. The pack is with Sanyo UR18650W and I selected entry 0219  in the Eval-Sw. After the cycles I created the golden image file.

    Just now I had a look at the ChemUpdater again and found that there is a second entry for Sanyo "18650 W" with ID 0204. What is the difference between this two entries?

    Today I found another issue with these packs:

    I charge the pack to full until FC is set. Remaining capacity is set to FCC and rel SOC is set to 100%. After connecting an electronic load with 6A the remaining capacity and RSOC jumps to ca. 50% although the pack is fully charged.

    When I unseal the pack and send 0x21 to manuf. access this does not happen. But I don't know if l this issue will come back again?

    Do you have some idea what goes wrong?

     

    Regards

     

    Michael

     

  • I still have big problems with this issue.

    I checked the DFI-Image file for the Chem-ID the wrong ID was in the Image-File. I don't know why, I was sure I selected it.

    Over the weekend I did the cycling with the new Chem-ID but the issue was the same as before.

    After charging the pack to full and let it rest for min. 2 h and than connecting a load to the pack, Full-Charge-Capacity jumps to some very low value. The pack discharges until cell-undervoltage but the LED-displays shows empty. After 5 hour relaxing the pack is charged, but it charges not to full, because the safety limit "Over charge capacity" is reached and the pack disables charging.

    For me its difficult to understand, why FCC changes with connecting the load.

    Also my question about the two entries for Sanyo W-cell are still open.

    I tried also the Chem-Select of bqEasy, but after the 24h test, when I click on "Match Best Chemistry" the application reports only "Runtime Error 9, Index out of Range."

     

    It would be very helpful to get support from TI, because we don't want do deliver packs with this issue.

     

    Regards

     

    Michael Houzer

     

  • Michael,

    I apologize for the delay in response. To help you further, we need your .gg file, as well as a data log showing what's happening before and after the events that you are describing. If you are uncomfortable posting them here, we can exchange them in a private message.

    Regards,

    Jason

  •  

    Jason,

    Again thank you for your answer. I will prepare the files for you and would prefer to send them by private mail to you. Do you need also the DFI-File?

    How can I send the files to you?

     

    Regards

    Michael

     

  • Michael,

    I've sent you a friend request. Once you accept it, you can send me a private message with the information. The DFI could be helpful too, so you can send that as well.

    Thanks!

    Jason

  • hi Michael & Jason,

    its sounds like we have the same problem. i would be very glad to know what is the final resolution.

    John

  • Hi John,
    It's been already long time you asked these questions. I'm working with bq20z65 now, I'm creating golden pack .DFI with bqEasy but I don't know yet how to write the file into the other packs? Can I simply load the file using the data flash screen and write the device memory? At what stage, after calibration and before enabling IT?
    Besides, bqTester is not compatible with this IC...
    I would be grateful if you or somebody else can answer to this question. There are several documents but they are not clear about this point.