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BQ78350-R1: The capacity is wrong

user5811580
Intellectual 700 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ76940, BQ78350, GPCCHEM, GPCCEDV

I have just made a BMS with bq78350 ,bq76940 and 12 batteries.

The full voltage of the batteries is 50.4V.

However, when the voltage drops to 49V, the capacity has drop to 0  which is showed as below.

Is anything wrong with my BMS.

Is there a way to fix it?

Besides, the voltage of all batteries and the current have been calibrated according to the manual.

  • 0
    TI__Guru* 81034 points
    Hi Wu,

    There are a few more steps involved to set up the gauging feature. There is an app note that will help guide you through these steps: www.ti.com/.../slua924.pdf

    First, make sure the AFE Cell Map is configured correctly. This is covered in section 2.1
    Next, load the correct ChemID for your battery, set the Design Capacity, and determine the CEDV gauging parameters for your battery and application (section 2.3).

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Intellectual 700 points

    Matt, thanks a lot.

    How to get the chemID of the battery?

    Just have a look at the battery listed as below.

    This group includes six batteries in all and the BMS is made up of two groups.

  • 0 in reply to user5811580
    TI__Guru* 81034 points
    Hi Wu,

    I do not see this specific battery in our ChemID database. There is an online tool (GPCCHEM) that can help you find the closest match: http://www.ti.com/tool/GPCCHEM There is also a video if you scroll down to the bottom of the GPCCHEM page to go along with the written guide.

    For some gauges that use Impedance Track technology, find the best ChemID is very important for gauging accuracy. For the BQ78350 (CEDV gauge), the ChemID is only used to determine initial conditions when the device is fully reset. It is used to best estimate the SOC from the voltage only. However, once the gauge is operating, it does not use the ChemID. Depending on your application, it may not be very critical.

    However, it is very important in all cases to go through the steps to set your CEDV parameters.

    Best regards,
    Matt
  • 0 in reply to Matt Sunna
    Intellectual 700 points

    Matt, during the charging process, the capacity is increasing. However, when the system is reset, the capacity just drops to 7%. For the discharging process, the capacity is also decreasing. However, when the system is reset, the capacity just drops to 7% too. Besides, the voltage is near 49V. Is it normal? Is there anything wrong with the system except the wrong ChemID ? 

  • 0 in reply to user5811580
    TI__Guru* 81034 points

    Hi Wu,

    If the capacity is showing as 7%, it might be because the voltage of one of the cells is below the EDV2 voltage setting in data flash. Or it could be related to the ChemID.

    To help debug the issue, can you send your data flash settings (.gg file) and a log of your charge and discharge with the resets?

    To save the dataflash settings, click on the Export button on the Data Memory window.

    To save a log file, click on the 'Start Log' button on the Registers window:

    Thanks,

    Matt

  • 0 in reply to Matt Sunna
    Intellectual 700 points

    Hi, matt.

    During the charging and logging process, should I wait for the voltage increasing to the full voltage, which is 50.4V?

    Is it the same for the discharging?

  • 0 in reply to user5811580
    TI__Guru* 81034 points
    Hi Wu,

    To collect the datalogs for the GPCCEDV tool, it is important to charge to full and then discharge down at least to the terminate voltage (~3V per cell or so). However, since we are trying to debug some issues you are seeing, the most important thing is to capture the events you described. It would be good to see a charge to full and discharge, but I also want to see the Resets which are causing the device to read 7%.

    Matt
  • 0 in reply to Matt Sunna
    Intellectual 700 points

    Thanks a lot, matt.

    I'll send all required files to you when ready.

  • 0 in reply to user5811580
    TI__Guru* 81034 points
    Hi Wu,

    I will close the thread for now since it has been a few days. If you respond to this thread it will automatically reopen, so you can respond once your files are ready to share.

    Thanks,
    Matt