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BQ40Z80: Learning Cycle Failing on Charge

Sean Chen79
Prodigy 215 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: GPCCHEM

I am having trouble getting the BQ40Z80 detecting a full charge.

I am charging a 6S 22.2V LiPo battery with a 1300mAh capacity. I set the design capacity settings (Design Capacity mAh = 1300mAh, Design Capacity cWh = 2886cWh, Design Voltage = 22200mV) The FC Set Voltage Threshold is set to 4200mV.

I set the ChemID and did the full discharge cycle as described by the Slua848 pdf and wait until the REST flag is set before starting the charge. I charge the battery all the way to 25.2V at a C/2 charge rate. The FC isnt set, and the battery is shown to only have a 31% charge. Remaining capacity is shown to be 1231mAh and Full charge Capacity is reported as 4097mAh.

What does the chip check to determine if the battery is at FC? Is it the voltage or is it comparing remaining charge to full charge capacity? Is there a setting I'm missing to configure?

  • 0
    TI__Guru 52115 points

    Hi Sean,

    See Section 5.7 Charge and Discharge Termination Flags in the BQ40z80 TRM for the details.

    Andy

  • 0 in reply to Andy Liu (BMS)
    Prodigy 215 points

    Hi Andy,

    Thanks for the link! I checked out that section and it looks like the voltage check should be triggering, but the RSOC is where the issue is. Remaining capacity is shown to be 1231mAh, which is pretty close to what is expected since the pack I'm using is advertised to be a 1300mAh pack. The problem seems to be that the "Full charge Capacity" is reported as 4097mAh. It's calculating the RSOC as 30%. It seems that the FCC is being calculated incorrectly. Is this most likely an issue with the ChemID or is there a setting that I might have entered incorrectly?

    Thank you!

    Sean

  • 0 in reply to Sean Chen79
    TI__Guru 52115 points

    Hi Sean,

    Did you get the chemistry id via the GPCCHEM tool? 

    Can you share your gg file?  Let me check your settings.

    Andy

  • 0 in reply to Andy Liu (BMS)
    Prodigy 215 points

    Andy,

    I picked out a ChemID from the preset table in bqStudios that best matched the chemistry (LiCoO2) and capacity (1300mAh) of my battery. I figured this would be close enough to let me test out a learning cycle and get the cell balancing working. Right now I'm just working with a smaller battery for testing purposes before I move on to the bigger battery that we'll be using for the final system.

    I attached the gg file.

    Thank you!

    Sean

    5444.test.gg.csv

  • 0 in reply to Sean Chen79
    TI__Guru 52115 points

    Hi Sean,

    I would sugget you use the GPCCHEM (http://www.ti.com/tool/GPCCHEM) to find the best matching chemsitry id. It is very necessary. You cannot choose a chem id based on the model name or capacity.Without a proper chemistry id, your learning cycle will most likely fail.  

    Andy