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BQ34Z100-G1: Strange full-capacity jumping on pulsed load with BQ34z100

richard mcdougall
Prodigy 185 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100EVM

I'm using the BQ34Z100EVM to monitor a 12 cell 40AH LIFEP04 pack.

The monitor works well, except that I see the following changes to FullChargeCapacity when the pack is close to full.

The IT algorithm seems to correctly readjust the predicted FullCapacity close to the design of 40.0AH, but with a pulsed load going between charge and discharge at full capacity the gauge seems to adjust FullCapacity up and down by 10%.

Do we know why this might be?

Richard.

  • 0
    TI__Guru* 76230 points
    HI Richard
    Is that the true FCC or the filtered FCC? What do you have your load select set to? I Would suggest setting it to present average discharge currrent if set otherwise.

    If you are still having issues, make sure to attach your log file showing the issue and a gg file so I can see your df settings.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 185 points

    I have the default load modes:

    Load Mode: 0

    Load Select: 1

    The load is a DC scooter motor, where the load varies from idle up to 70amps and back to zero in long or short bursts depending on speed/acceleration etc.

    Would load-select 3 (filtered) be better in this application? Is there a guide about which load-select to use?

    Thanks,

    Richard.

    burnerboard.gg.gz

  • 0 in reply to richard mcdougall
    Prodigy 185 points
    The fullcapacity is the parameter from 0x06/0x07. How would I know if it's filtered?

    Thanks
  • 0 in reply to richard mcdougall
    TI__Guru* 76230 points
    what file extenion is .gz? how do extract the files? Have you performed a learning cycle and did you ensure the chem id being use is the right one?
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 185 points

    Hi Onyx,

    Yes the chemID is set to 406 for LifeP04 and many learning cycles have completed. The gauge seems to adjust correctly when it's only doing OCV, it seems to have issues under charge/discharge load.

    Sorry that was gnuzip, here is regular zip.

    Thanks for your help!

    Richard

    burberboard.gg.zip

  • 0 in reply to richard mcdougall
    Prodigy 185 points

    In case it's helpful -- here is the voltage / capacity data when the charger is being pulsed every 5 minutes .

  • 0 in reply to richard mcdougall
    Prodigy 185 points
    I don't have any data for during operation with high current (because the device is mobile), but I have observed jumps in full capacity of +/- 30%. This results in early prediction of battery empty. I would love to get some thoughts about what could cause that.
  • 0 in reply to richard mcdougall
    TI__Guru* 76230 points
    Hi Richard,
    A log file would be really useful to have an idea of what is going on. Can you use an electronic load to simulate your load profile to allow you log data.?

    The fist thing that comes to mind is the fact that FCC by definition varies with current due to the internal impedance of the battery. The greater the current, the greater the IR drop and the lesser the FCC. This is an inherent characteristic of the battery. However, I can't say for sure if the 30% reduction in FCC is actual due to the high discharge current or if the guage is inaccurately reporting FCC. You can actually discharge the battery from full charge to empty using that high current and then coulomb count the passed charge using the gauge to be able to determine what the capacity of the battery would be under that high current. This will let you know if what the gauge is reporting is correct or not.

    Again i have to emphasize that without a log file, I will only be speculating. It is important that you try to get one showing the problem.

    thanks
    Onyx