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Original question:

BQ35100: Characterisation for LiSOCl2 battery

BQ35100EVM-795: How to measure remaining capacity of a Li-SOCI2 with BQ35100EVM and BQStudio

Patrick Chaopricha
Prodigy 25 points
Part Number: BQ35100EVM-795
Other Parts Discussed in Thread: BQSTUDIO, EV2400, BQ35100

I have the bq35100EVM board connected to the EV2400 and started BQstudio.  I updated the Configuration Operation Config A to set EOS mode with GMSEL1 = 1 and GMSEL0 = 0.  I updated battery chemistry to ID = 0608 which is what I have (Li-SOCl2 (LTC), 3.6V, 19000 mAh).  The bq35100EVM has the Bat+ and Bat- connected to my single cell LTC battery.  I also have a connector for the load with Bat+ to Load+ and Pack- to Load -.  The bq35100EVM has a jumper in the GE_PULL-UP and ALERT/PULL_UP.  S1, S1 have jumpers on them.  For J3, I leave the jumper on 2S since it probably doesn't matter due to not using the 2-4S selection.

*Note: my LTC battery is not new and it's probably about 80% depleted and that's what I want to be able to check with the EOS mode.

I followed the procedure from another post someone talked about measuring the LTC here:

1) Power bq35100EVM to get GE enabled by putting in the battery.  Check that BQStudio sees the bq35100 with no issue
2) Plug the load in with the connector.  I can see it's drawing -17 mA on average.   Check that EOS_BAD_OCV and GA are both still green.  I click the GAUGE_START button in BQStudio.  
     - At this point, I see the EOS_BAD_OCV and GA turned red.   (I don't know whether this is good or not.)


3) I unplug the load and let the battery relax for a minute or so then send the GAUGE_STOP.  Wait a few seconds for the status update.

4)  I see the impedance calculated as 7.341 ohms.  The SOH is updated to 90% but I don't know whether that's right.   

Am I doing this correctly?   Do I need to do this first with a fresh new battery?  Why does the design capacity stay at 2200 mAh even though the chosen battery chemistry ID 0608 should have given it 19000 mAh.

Thanks,
Patrick

  • 0
    TI__Guru 57697 points

    Hello Patrick,

    You need to start with a fresh battery, Design capacity needs to be set separately from battery chemistry since the same chemistry cells can be placed to parallel for gauging with  bq35100

  • 0 in reply to Shirish
    Prodigy 25 points

    OK, I'll get a brand new battery and run this through again.  How do I measure the capacity of the near-depleted one after I got the new one measured?

  • 0 in reply to Patrick Chaopricha
    TI__Guru 57697 points

    Hello Patrick,

    The bq35100 expects a new battery and tracks the capacity of a single battery. Connecting a depleted battery is not expected.

    You may be able to get capacity of a depleted battery after running a few cycles as per the Battery Gauging modes. For EOS mode see TRM section 5.3.2 End-Of-Service Detection

  • 0 in reply to Shirish
    Prodigy 25 points

    Hi Shirish,

        If I understand correctly, the EOS mode is to track a new battery until it's depleted, correct?  Does this mean that the gauge has to pretty much stay on with the battery and do occasional readings on the battery to determine its EOS?  When a new battery is put in then I need to issue the NEW_Battery command to start the tracking of the new battery?

        Could you clarify what the Battery Gauging mode is?   There are accumulation mode, state of health mode (SOH), and End of Service mode (EOS).  I noticed that in the SOH mode, I couldn't get the battery current reading like the EOS mode does.  So how do you run the Battery Gauging mode?  I'm unsure from reading the documents (both the User's manual and the  bq35100 Technical Reference manual.

        I was hoping that I could use the bq35100 to determine LTC battery's remaining capacity since it's not easy to determine a remaining capacity of an LTC battery without discharging it and deciding.  Since it's single-use, draining it pretty much means it's done.  I suppose that's OK if I do it on one battery that was in parallel with the other ones and use the drained one as a proxy for the remaining capacity of the other cells.

    Thanks,
    Patrick

  • 0 in reply to Patrick Chaopricha
    TI__Guru 57697 points

    Hello Patrick,

    The gauge must stay with the battery.

    The different modes and how to set the mode is in chapter 5 of the TRM

    Gauging mode refers to one of the 3 modes of operation

    0 0 = Enables ACCUMULATOR mode

    0 1 = Enables STATE-OF-HEALTH VOLTAGE CORRELATION mode for LiMnO2

    1 0 = Enables END-OF-SERVICE RESISTANCE CORRELATION mode for LiSOCl2

    On one test battery:

    You will set all parameters and configure as per the selected mode of operation. Then take a "golden image". Verify the accuracy of this golden image by using with a battery. If good, then program this golden image to each

    On each battery:

    When the battery is ready to be deployed, send the NEW_BATTERY command.

    The host must send enable the gauge/ send Gauge_Start and Gauge_Stop commands to let the bq35100 know when to turn on and monitor/take readings.