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BQ40Z50-R1: Higly pulsed discharges and Ra update

Ragnar Wallebom
Prodigy 60 points
Part Number: BQ40Z50-R1
Other Parts Discussed in Thread: BQ40Z50, BQSTUDIO

We are using a bq40z50-R1 with highly pulsed discharges. (0.1 - 1s at 20-40A) on high current 18650 cells. We find Updatestatus = 4 and MaxError go to 100% and hard to reset unless we do charge and "nice" continous discharges.

Are "nice" discharges a requirement for Maxerror staying at 1% over time?

Any tips to optimize capacity estimation with highly pulsed loads?

  • 0
    TI__Expert 6575 points
    Hi Ragnar,
    Once the golden image is programmed to the gauge after the initial learning cycle when "Update Status" is updated to 06 or 0E and "Max Error" is updated to 1%, these should not change automatically to "Update Status" 04 and "Max Error" of 100%.
    During the learning cycle to create the golden image, you will have to use constant current or power discharge, but this does not have to be performed on every pack.
    Here are some useful links for doing the learning cycle and creating the golden image:
    www.ti.com/.../slua777.pdf (applicable to bq40z50 as well)
    e2e.ti.com/.../Taking-your-fuel-gauge-from-design-to-production.pdf

    Regards,
    Swami
  • 0 in reply to Swaminathan Ramanathan75031
    Prodigy 60 points

    Thanks for your reply but not sure the answer is relevant to our case. I think you're saying we didn't do the learning cycle/golden file/parameter setup correctly.

    I however assume MaxError can be 100% if left with no activity for long time? (in tech ref 14.13:

    The Configuration:Max Error Time Cycle Equivalent period passed
    since the last valid QMax update    		 MaxError() increment by 0.05%

    The problematic batteries have been stored at low SoC for long time. GaugeStat[CF] is set indicating (Conditioning Cycle requested). What is it and how can we perform this? Similar to learning cycle but used as an recover/update?

    Some batteries have been suceessfully returned to MaxError 1% and UpdateStatus to 6 by cycling, but we don't understand what makes only some do this.

    Also we cannot make the Qmax update even when following instructions for this (6.4.2 QMax Update Conditions in tech ref.). REST, VOK, oCVFR flags and other conditions are met.

  • 0 in reply to Ragnar Wallebom
    TI__Expert 6575 points
    You are correct, the MaxError() will increment over cycles and time if the Qmax does not get updated.
    However, it is very unusual to see it increase to 100%. (With the default value for "Time Cycle Equivalent" of 24hrs, it will take about 5.5Years, or 2000cycles, without Qmax updates to reach 100%)
    Also, the Update Status will not be automatically changed by the firmware from 06 or 0E to 04. If Update status changes to 04, it is probably getting written to that value.
    The Gauge status [CF] is set when MaxError() >= Max Error Limit (Condition Cycle Needed). The default value for Max Error Limit is 100%. This indicates that Qmax update has not happened and that there should be a discharge or charge of >37% change in DOD outside the flat region of the cells to update the Qmax.
    Is it possible to post the log file using bqStudio of a failing cycle as well as your gg file. this will help debug this issue further.
    Regards,
    Swami