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BQ28Z610-R1: Single cell LiFePo4, full charge capacity issue

Ondrej Teren
Prodigy 20 points
Part Number: BQ28Z610-R1
Other Parts Discussed in Thread: BQ28Z610, GPCCHEM

Tool/software:

Dear Sir or Madam,

We would like to ask you for help.

We are trying to use BQ28Z610 with single cell LiFePo4 cell (400mAh, 3.2V design voltage) and we are facing some issues with updating the full charge capacity on start-up of the new discharge cycle. We set up all necessary values of our systems and finished the learning procedure up to the 0x0E status.  We had a lot of success in previous projects but with classical 3.7V Li-Ion batteries.

The situation is that the Cell 1 QMax is almost correctly calculated to the 460 mAh and the Full Charge capacity is set to this value somewhere during the learning cycle. But when the procedure is finished and we start the first discharge cycle the full charge capacity drops immediately to value 83 mAh (or something like this).  And then for sure the gauging is not correct.

Also we have an issue seeing the FC bit set (FD is OK). Even we set up all values correctly. The used charger IC is: BQ25071QWDQCRQ1 (this charger has a little overcharge peak)
Our batteries are 2p: ENERpower 10430 LiFePo4 3.2V 200 mAh

We are using 0x4137 chem ID. 



Important setting is as follows, maybe you can see some discrepancy in our setting. Attaching the Data memory export.


Many thanks for help.

1bq.gg.csv

  • 0
    TI__Mastermind 26621 points

    Hello, 

    Can you also provide me with a log file that shows this behavior? Additionally, how was the chemID matched for this, did you use the GPCCHEM tool? 

    Regards, 

    Robert. 

  • 0 in reply to Jonny
    Prodigy 20 points

    Dear Robert,

    We moved a little bit further with the FC bit setting. The problem is in the connection with this particular charging IC, cause it has no charging current slope. As it is shown here:



    It just removes the whole current in one moment and as we read the criterias for FC bit setting this is in conflict with this moment. So we tried to charge the battery with laboratory supply with CC/CV profile and now the FC bit is setting. 

    Regading the CHEMID, we will try to make a whole log for the CPCCHEM and I will get back to you with log and also with the result from GPCCHEM.

    One question, can you sum up what values which should be adjusted prior to the usage of this gauge for LiFePo4 (or generally for cell with much lower charging voltage than normal 4200mV)? I know about the values which are in Learning cycle guide, but we are wondering (for example) if also these values should be adjusted as well?



    Do you have some guide what should be all set up with cells with 3,5 or 3,6V charging voltage? In the meantime, we will try to log the data for Chem ID tool and upload to the system.

  • 0 in reply to Ondrej Teren
    Prodigy 20 points

    For now, we have charging part of the log, where is obvious the jump from good remaining capacity (cca 400mAh) to the bad one during FC set bit.  I am attaching. At least this is weird. Now I am in relax progress and the log continues, then I will discharge and relax again for complete log. I will get back to you with complete log.

     chargeFC_to99mAh.log

  • 0 in reply to Ondrej Teren
    TI__Mastermind 26621 points

    Hello, 

    Let's start with the chemID and successfully completing a learning cycle in regards to what parameters we should tweak. Please update this thread once you have completed this. 

    Regards, 

    Robert. 

  • 0 in reply to Jonny
    Prodigy 20 points

    Yes, but for the new learning cycle, we will probably need at least this:

    Do you have some guide what should be all set up with cells with 3,5 or 3,6V charging voltage? 

  • 0 in reply to Jonny
    Prodigy 20 points

    Dear Robert, we received information from chemID tool, and setting up the 0x0400 chemID helped a lot. Now the charging/discharge cycles looks better. Anyway can you point out if we have a new chip which values should be set prior to the learning cycle, if we are going to use cell which has no 4,2V Charging Voltage but 3,5 or 3,6V. Thank you for your kind help with this.