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BQ40Z50-R1: Problems performing a Learning Cycle

Peter Hawkins
Prodigy 100 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQSTUDIO

Hi,

I am developing a customer board with two cells which includes a BQ40Z50-R1. The cells are marked INR26650 3.6V 5000mAhr 18Wh. I'm told that they are Li-ion cells.

I have tried to set everything up in BQ studio as best I can and have performed various charge and discharge cycles which seem to be working as expected. As expected for a new system, the CF flag is set indicating a learning cycle is required. I have tried performing this but I've been unable to get the LStatus flags to change up from 0x04.

The learning process I've been following comes from another post here and goes as follows:

  1. Configure the dataflash with appropriate parameters suitable for customer's application; configure pack's chemistry and perform calibration.
  2. Activate impedance track.
  3. Charge the pack to charge termination.
  4. Allow the pack to rest until the REST flag sets.
  5. Discharge the pack at a C/10 to C/5 rate to the Termination Voltage.
  6. Allow the pack to rest until the REST flag sets. Qmax should update and Update Status should increment to 05.
  7. Fully charge the pack to charge termination.
  8. Allow the pack to rest until the REST flag sets.
  9. Discharge the pack at a C/10 to C/5 rate to the Termination Voltage.
  10. Allow the pack to rest until the REST flag sets. The Ra table should update and Update Status should increment to 06.

I'm getting stuck at item 6. The REST flag is being set and I'm getting Qmax updates but LStatus in staying stuck on 0x04 even though it has been in this state for over 20hrs.

Note: The above instructions use the term Update Status. I have assumed that this is the same as the LStatus register (4 x undefined bits, Field_Qmax, ITEN, CF1, CF2).

Srec File:  Failed Learning Cycle.zip

.gg.csv File: Settings #11 - Failed Learning Cycle.gg.csv.zip

First Discharge Cycle: Charge discharge cycle log #3.log

First Chage Cycle: Charge discharge cycle log #4.log

Second Discharge Cycle: Charge discharge cycle log #5.log Probably the better one to look at.

Second Discharge Cycle continued: Charge discharge cycle log #6.log Next day resting.

I'm sure that I've missed something silly but I've been through everything now a few times and can't spot what I'm doing wrong. Any help would be greatly appreciated.

Thanks, Colin

  • 0
    TI__Mastermind 34775 points

    Hi Colin,

    We will try to review your files and respond on Monday. In the mean time please read the TRM section 6.4 QMax and Ra  and learning cycle guide.

    4024.LearningCycleOverview.pdf

  • 0 in reply to Damian Lewis
    Prodigy 100 points
    Hi Damian,

    Thanks for looking into this for me. Your Learning Cycle Overview includes some useful stuff I hadn't found elsewhere.

    Could you confirm that "LStatus" (used in bqStudio and 13.1.55 of the TRM) is the same as "Update Status" (used elsewhere)?

    Looking through the list of "Common Problems During a Learning Cycle"

    - Battery not detected.
    I can't find the BAT_DET flag on the BQ40Z50-R1

    - IT not enabled.
    IT = '1'

    - Not reaching full charge.
    FC = '1' at end of charge.

    - Not relaxing long enough.
    VOK = '0'

    - Discontinuous discharge.
    Discharge was performed all in one go.

    - Discharging too far.
    This is a possibility as I don't fully understand the requirements. Fuse is disabled so "Pack Protector Opens" shouldn't happen? "Gauge goes into POR" I don't understand. POR is used in the TRM in a few places but isn't defined. It appears to mean "Power On Reset" in the TRM but I could be wrong.

    - Not relaxing at all.
    It now has three days of relax.

    - Too much current during relax.
    Doesn't appear to be the case.

    - Not at room temperture
    Temp = 20 deg C.

    - FET doesn't cut off discharge.
    Load was removed manually.

    - Wrong chemID selected.
    This is a possibility. I can't find a RUP_DIS flag on the BQ40Z50-R1

    - LiFePO4
    not using LiFePO4

    All help gratefully received.
  • 0 in reply to Peter Hawkins
    Prodigy 100 points

    Peter Hawkins said:
    Hi Damian,

    - Discontinuous discharge.
    Discharge was performed all in one go.

    I was thinking about this last night and it isn't strictly true. The discharge was performed until the CUV point was reached (2.9V per cell). This caused the discharge FET to switch off stopping the discharge. A short while later, the cell voltage recovered to the CUV recovery point (3.1V per cell) and the discharge then restarted. This cycle repeated a couple of times before I noticed it was happening and removed the load manually.

    Would this process invalidate the discharge cycle?

  • 0 in reply to Peter Hawkins
    TI__Mastermind 34775 points

    Hello Peter,

    The learning cycle guide doesn't  100% apply to bq40z50-R1 in terms of some of the flag names. It's more a procedure guide.  RDIS is RUP_DIS flag. I suspect you have the wrong chem ID for your cells. You can use our online GPC tool to help you find the best matched chem ID for your cells before doing the learning cycle by following the guide below.

    Simple Guide to Chemical ID Selection Tool (GPC)

  • 0 in reply to Damian Lewis
    Prodigy 150 points
    Thanks Damian,

    We will gather new data and run it through the GPC on Monday. Hopefully that will get us over the problem.

    Cheers, Colin

    (Now on my own account having finally sorted out the login problem. Why does the forum allow you to create an account with a 16 digit password but only lets you login with a max of 12?)
  • 0 in reply to Colin Bathe
    TI__Expert 5090 points

    Hi Colin,

    I'd like to understand your issue about the password length, we checked but didn't see that offhand.  Can you describe in more detail exactly where you setup and used the password?

    Thanks,

    Terry

  • 0 in reply to -Terry
    Prodigy 100 points
    I've had a little look and it appears to be an interaction with LastPass. I had LastPass set up to generate 15 character passwords and it was pasting the password into the field fine. I didn't notice that the page had chopped off the last three characters. This meant that LastPass stored the 15 character version whilst your end only stored 12. When I came to login, it then didn't work.
  • 0 in reply to Peter Hawkins
    TI__Expert 5090 points
    Thanks! We'll take a look and see if we can improve things to avoid this type case in the future.

    Terry