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BQ78350-R1: Remaining Capacity after ShutDown or reset

Pierrick Thevenaz
Prodigy 240 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350,

Dear all,

I did the data collection for the GPC and I received the coefficient back by TI. I assume that BQ78350 CEDV is not compatible with VOC75, VOC50 & VOC25 because I did not find any register to put them, right?

So, after putting the new coefficients, I tought that it will resolve my Remaining Capacity issue after a shutdown or reset, but it did not.

After a Full Charge, my Remaining Capacity is 19588mAh with 100% on the Gauge what is correct. I have the autoship enable and my battery goes in shutdown automatically after 120min. When I wake up the battery, the cell voltage is almost the same but the Remaining Capacity is now 15152mAh with 78% on the Gauge!

The ChemID is 2039 for Panasonic NCR18650BF. By the way, there are two different ChemID for the same cell and I do not know the difference.

What can I do to have an accurate Remaning Capacity after a shutdown or reset?

BR,

Pierrick.

  • 0
    TI__Guru* 76230 points
    Pierrick,
    Can you pls share the files of what you submitted to gpc and the results that gpc emailed you back?

    thanks
    On
  • 0 in reply to Onyx Ahiakwo
    Prodigy 240 points

    Hi On,

    Yes, here are the files.

    BR,

    Pierrick

    GPCPackaged.zipGPCPackaged-report.zip

  • 0 in reply to Onyx Ahiakwo
    Prodigy 240 points

    Here is also the gg file if needed.

    BR,

    Pierrick.Config_V080_CEDV_104_20062017.gg.csv.zip

  • 0 in reply to Pierrick Thevenaz
    TI__Guru* 76230 points
    Hi BR,
    Now that i re-read your question, i realize that you are putting the gauge in shutdown mode or resetting.. Doing that means you will loose all passed charge data and the gauge would have to reinitialize. Because this is not an Impedance track algorithm gauge but rather CEDV, it doesn't have the 40 grid point OCV table that IT uses but rather a 10 grid point OCV table to determine SOC and rem cap. So upon exit from shut down the accuracy of the gauge wouldn't be the best because the 10 grid point OCV doesn't have enough interval to guarantee a high level of accuracy.The gauge can only get back to reporting accurately if you charge the cells to full or discharge to the EDV thresholds andNot shutting it down or resetting it again .

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 240 points

    Hi Onyx,

    OK, I understand that CEDV gauge has only 10 points OCV and after a reset or shutdown, those 10 points determine soc and remcap until an EDV threshold.

    But the battery is going in shutdown mainly after a full charge and I want to see 100% when I wake up it. At the moment, after a full charge and a shutdown, the gauge indicates 78% which is very far from the reality.

    Is there a way to increase this 78% to 100% with a gauge parameter, like a value offset? Or maybe some parameters should not be let to the default value like Low BAT% or something else.

    Thanks,

    Pierrick.

  • 0 in reply to Onyx Ahiakwo
    Prodigy 240 points

    Hello,

    I have not received any response on my last post. I really need to know if it is possible or not to have a remaining capacity of 100% soc and a more or less accurate remaining capacity after a full charge and a shutdown or reset. Because I have several projects with this chip and I am stuck with this problem.

    Thanks best regards.

    Pierrick.

  • 0 in reply to Pierrick Thevenaz
    TI__Guru* 76230 points
    Pier-rick,
    No it is not possible that the gauge will read 100% after wake up from shut down. This is because you coulomb count to 100%, after charge terminate is reached and charger is removed, voltage relaxes downward, so no way you can do voltage correlation and get 100% after wake up from shutdown.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 240 points

    Hi Onyx,

    That is not a good news for me!

    I understand that the cell voltage relaxes after full charge and 100% is not possible. But the gauge indicates only 78% after a reset, which is very low. If refer to the OCV table that I have received back from GPC, 78% is corresponding to a cell votlage of about 3923mV. I just restarted my battery after 5 days and all the cells volatge are about 4170mV, so according the OCV table, the gauge should indicates 99 or 98%, not 78%! For me, something is wrong, no?

    Here is a copy of paragraph 9.1.5 of the technical reference:

    9.1.5 Initial Battery Capacity at Device Reset
    The bq78350-R1 estimates the initial capacity of a battery pack at device reset, which is the case when
    battery cell(s) are first attached to the application circuit. The initial FCC is a direct copy of Full Charge
    Capacity. The initial RC and RSOC are estimated using the open-circuit voltage (OCV) characteristics of
    the programmed Li-Ion chemistry (default ID1210), DOD at EDV2, and Learned Full Charge Capacity.
    When assessing the RC vs. OCV correlation, the bq78350-R1 uses the applicable CellVoltage1..15() data
    even if ExtAveCellVoltage() data is available. Upon the update of RC and RSOC based on the OCV data,
    the BatteryMode() [CF] flag will be cleared. This gives a reasonably accurate RSOC; however, battery
    capacity learning is required in order to determine the most accurate FCC, RC, and RSOC.


    My "Dod at EDV2" is 11436? It is a correct value?  And "Battery Low%" is 7%.

    Best regards,

    Pierrick.