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BQ20Z45-R1: SOH% reported as lower than Relative SOC% after running the Golden Cycle (battery looks aged due to reserve capacity?)

Randy Carpenter
Prodigy 20 points
Part Number: BQ20Z45-R1
Other Parts Discussed in Thread: BQEVSW, BQ40Z50

Hi,

What can cause SOH% to be reported as lower than Relative SOC% after running the Golden Cycle?

8% of aging on a new battery seems wrong.

It seems FCC is reduced by Reserve Capacity. The TechRefManual says that is normal. But State of Health is diminished due to Reserve Capacity it seems. Logically that seems abnormal.

While trying to run a Golden Cycle(using bqEVSW), VOK is not clearing after Full Charge has relaxed and 5 hours has passed. Even after 1 ½ days it didn’t clear. I use the sequence in SLUA334B and am familiar with SLUA 597 but I could not find the solution in that app note. Within the relaxed 5 hours, battery voltage remained constant to the mV over more than 1000 seconds. I let it Relax much longer than 5 hours, but Vok did not clear. MAX ERROR remained at 100% and Update Status remained at 4.

I will attached a zip file with logs for debug.  I don't see where to attach files on this form so please also give me some guidance on where I can attached the zip file with .senc , .gg and log files?

Best Regards,

Randy

  • 0
    Prodigy 20 points

    zip file with .senc, .gg and log files is located on case CS0503106.

    Best Regards,

    Randy

  • 0 in reply to Randy Carpenter
    TI__Genius 10370 points

    Randy,

    I see your chemID you are using is a LiFeP04 cell type. This type of chemistry has additional relaxation rules associated to it and a very large "flat zone". The Flat zone is disqualified from learning due to the large error the voltage measurement produces.  Debugging These use cases is very difficult on this old device. This device is not recommended for new designs and the bq40z50 is the one we recommend. For this ID the flat zone starts at 3334mV. If you voltage doesn't leave charge mode 50mV above this then you will be within the flat zone and disqualified. 

    I suggest charging to a higher voltage down to a lower current to get above this flat zone to see if you can get VOK to toggle. or swap to the bq40z50 where there are some better features to try and deal with gauging these types of cells. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 20 points

    Hi Eric,

    I'm using chemID 0494.  Do you have the specific data regarding the flat zone for chemID 0494?

    I'm still not seeing VOK toggle upon completion of the relaxation process.

    Best Regards,

    Randy

  • 0 in reply to Randy Carpenter
    TI__Genius 10370 points

    Randy,

    The flat zone is 3334mV to 3278mV. However there is also a hysteresis. You need to leave charge mode above the flat zone + 50mV. 

    Please do this. Charge to full, let rest 5 hours, reset gauge, then send IT_enable command twice. This will force a DOD0 update and would clear the 48h hold. I do not recommend this outside of a VERY controlled environment. 

    Thanks,

    Eric Vos