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BQ40Z50-R2: Learning Cycle

JeremyG
Intellectual 631 points
Part Number: BQ40Z50-R2
Other Parts Discussed in Thread: GPCCHEM, BQSTUDIO, GPCRA0

Hi,

I'm having trouble with the learning cycle for some LiFePO4 packs I am working on.

I get up to 4.2.4 of SLUA848, but although RDIS clears, VOK remains set and LStatus at 4, even if I wait 48 hours.

Is this potentially related to the OCVFR flag that is set and if so, what is the 'cost' of bypassing this test to get a rapid QMAX - is it in terms of accuracy?

Any advice on this matter welcomed.

Thank you,

Jeremy.

  • 0
    Intellectual 631 points
    I ended up clearing the LFP_Relax bit in the IT Gauging register and then the QMAX update occurred.

    What is the consequence of taking this action - will accuracy be degraded? Is there something else I can try to have the QMAX update occur even with the LFP_Relax bit set? Would raising the charge voltage allow me to avoid the Flat Voltage Region and is there a way of inspecting the chemistry file to see what the range of this region is?

    Thank you,

    Jeremy.
  • 0 in reply to JeremyG
    TI__Mastermind 42535 points
    LFP relax uses a different method for calculating OCV during relaxation. Please refer to the TRM page 59 for reference. Yes, this affects accuracy slightly depending on if your chem ID was identified correctly.

    We don't allow access to OCV flat region data as that is TI proprietary.
  • 0 in reply to Batt
    Intellectual 631 points

    Hi Bat,

    I've read the LFP_RELAX paragraph on page 59 several times, but this hasn't solved my problem.  I simply can not achieve QMAX update, as per 4.2.4 of SLUA848 when I have the LFP_Relax bit in the IT Gauging register set, so I'm looking for suggestions on where else to look in terms of configuration.

    Thank you,

    Jeremy.

  • 0 in reply to JeremyG
    TI__Mastermind 42535 points
    How long are you in relax mode? LFP takes longer than usual and requires a proper LFP chem ID. Did you use GPCCHEM for a match? If not, please do that first.
  • 0 in reply to Batt
    Intellectual 631 points

    I have waited over 48 hours and have used the chemistry file that TI provided with bqstudio for the exact cells that I am using (K218650P), so I have not needed to use GPCCHEM

    Regards,

    Jeremy.

  • 0 in reply to JeremyG
    TI__Guru* 76230 points
    hi Jeremy
    if you are unable to get learning to be succesfu, instead of wasting additional time, simply use our online tool gpcra0 to obtain your golden file.
    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 631 points

    Hi Onyx,

    I'll give that a try later and then update this thread - thank you for the suggestion - perhaps the process will assist with troubleshooting my configuration.

    If you can think of any other aspects of configuration that can prevent the QMAX update from occurring, please let me know.

    I assume the 48 hour relaxation method invoked by setting the LFP_RELAX bit has been tested?

    Regards,

    Jeremy.

  • 0 in reply to JeremyG
    TI__Mastermind 24870 points
    Hello Jeremy,

    The 48 hour relaxation method has been tested for specific LFP cells, however, each cell may be a little different. The overall chemistry relaxation should be the same.
  • 0 in reply to Kang Kang
    Intellectual 631 points

    Hi Kang Kang,

    Do you have any further suggestions for parameters I should review that could prevent the QMAX update?

    Would it help if I sent in some files?

    Regards,

    Jeremy.

  • 0 in reply to JeremyG
    TI__Mastermind 24870 points
    Hello Jeremy, yes if you have your learning cycle log file or the cycling log file, it would help. Make sure it is a well-relaxed cell when you start logging. Then perform the test. Also make sure you are measuring the correct surface temperature of the cell by having thermistor NTCs attached.