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BQ40Z50: the batteries connected to the bms are empty in a few weeks

rob schoonen
Prodigy 50 points
Part Number: BQ40Z50
Other Parts Discussed in Thread: GPCCHEM, GPCCEDV, BQSTUDIO

Hi,

I never used a BMS before, but I have a pcb with a BMS (BQ40z50)  and a charger (LT1510-5CGN) .

This was designed by someone else,  I only know that I am supposed to load a .srec file and charge/ discharge the batteries.

I have done this, and it seems to be working, but after  ± 3 weeks not using the device, the batteries were empty.

The batteries were fully charched when the device was swiched off, (mechanical switch so no leakage current there) but after ±3 weeks the batteries were empty.

How can this be happening,  

Second problem is that the battery status is not remembered correctly.

When charging, the battery status seems ok, but when everithing is switched off, the next day the battery status is indicating a empty battery, but when messering the actual voltage the battery is still 95% full.

How can i solve these problems?

  • 0
    TI__Guru* 76230 points
    hi Rob,
    You will needd to identify your chem id and perform a learning cycle for the gauge to be accurate. When the gauge wakes up from shuttdown, it relies on an open circuit voltage measurement to be be accurate. depending on how well relaxed your battery it, you SOC accuracy will be fairly good.

    pls refer to the link below for chem id identification :
    www.ti.com/.../GPCCHEM

    refer to the app note below on how to perform a learning cycle.
    www.ti.com/.../slua777

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 50 points
    Hi,
    I created a log file according technical reference SLVA725 and send it to www.ti.com/.../gpcUpload.tsp.
    I get an email back with error messages.:

    Thank you for your interest in the Gauging Parameter Calculator from TI.
    There was an error in processing your report. The specific error encountered is:

    There was a problem with the content of the zip file.
    • Invalid Zip File Member - roomtemp_rel_dis_rel .csv
    • Required file 'hightemp_highrate.csv' is missing from the input zip file.
    • Required file 'roomtemp_lowrate.csv' is missing from the input zip file.
    • Required file 'lowtemp_highrate.csv' is missing from the input zip file.
    • Required file 'lowtemp_lowrate.csv' is missing from the input zip file.
    • Required file 'hightemp_lowrate.csv' is missing from the input zip file.
    • Required file 'roomtemp_highrate.csv' is missing from the input zip file.


    But according to the technical reference SLVA725 only a log file with time, voltage, current, and temperature is needed.

    How can I get a chem id file?
  • 0 in reply to rob schoonen
    TI__Expert 3990 points
    We have multiple GPC tools, this looks like you used the GPCCEDV tool, vs you need to use the GPCCHEM tool instead.
  • 0 in reply to -Terry
    Prodigy 50 points
    Hi,

    After making some changes to my datafile, I received a GPC report file from TI, advising me to use chemical ID 148.

    I charged and dis-charged my battery using chem ID 148, and now the SOC indication looks allright.
    But the BQ40z50 is still consuming to much current.
    I placed a current meter in the ground path to the cells. When applying a load, the current measures about 70mA.
    I then removed the load, the current drops to about 1.7mA.
    My battery is 1550mAh this means that my battery (when not used) will be completely empty after 1550/1.7 = ±38 days.

    According to the datasheet of the BQ40z50 Inormal = 336uA, Isleep=75uA and Ishutdown=1.6uA.
    Why do i measure 1.7mA? I expected to measure ±336uA
    When i use the shutdown button in bqstudio (1.3.52) the current drops down to 28uA. This is also more then the 1.6uA from the datasheet.

    Can anyone tell me why the bq40z50 is drawing to much current?
  • 0 in reply to rob schoonen
    TI__Guru* 76230 points
    Hi Rob,
    You will need to carefully review your schematic to verify where this current drain is coming from. Do you have an EVM for comparison purposes? Can you swap the IC on your board to verify if the IC is the problem?

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 50 points
    Hi Onyx,

    I discovered another component on my pcb which was drawing to much current, when I removed it the current in normal mode became
    ±350uA.
    It looks like the problem is solved.

    Thanks for your support.

    Rob.