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Chemistry ID

J.C Chen
Expert 1285 points
Other Parts Discussed in Thread: BQ27520EVM

Dear all

     In the  Application Note SLUA372 "Support of Multiple LI-Ion Chemistries with impedance track ", the report decribes the process of selecting the correct chemistry ID for a particular cell. There are five steps for the test.

Step 3: Discharge at C/20 rate for 1 hour, then go to step 2. If the voltage goes below 3V, go to step 4

Step 5: Discharge at C/60 rate for 30 min, or until V<2.7V; go to step 4..

I am a bit confusion about the these two description( step 3 in particular). Should i check the cell voltage during the C/20 rate discharge or check the cell's voltage after  1 hour? 

And same to step 5..

Best regards

Jason

  • 0
    TI__Expert 3865 points

    There is a simple way to do chemistry matching.

    Please refer to http://www.ti.com/litv/zip/sluc138

    The test is simply checking the battery pack to full (taper at C/100)->wait 2hr->discharge at C/10 to EDV-> wait 5hr. You can refer to the pdf of from the link for detail. Use EVSW to log the data and load the datalog into matchcad file for analysis

  • 0 in reply to Jackie Hui
    Expert 1285 points

    Hi, Jackie

        In fact, I used the method you recommended before. Now i want to re-check the result...Present I check the voltage during the discharging..

        I am not sure if it is accurate.

    Best regards

    Jason

  • 0 in reply to J.C Chen
    TI__Guru 73830 points
    Jason, The intent of the procedure is to discharge the pack to the termination voltage, which is a 3V cell voltage in the procedure. The Arbin tester monitors the cell voltage during its' testing. You can monitor the voltages and stop the discharge after the termination voltage has been reached, even if the one hour time has not elapsed. I hope that this helps. Tom
  • 0 in reply to ThomasCosby
    Intellectual 660 points

    Though this post is quite recent, the link http://www.ti.com/litv/zip/sluc138x is NFG.  I'm finding the vaunted Impedance Track technology quite difficult to implement.

    Bob

     

  • 0 in reply to Bob White
    TI__Guru 73830 points

    Bob,

    There was a typo in the link. The correct link is:  http://www.ti.com/lit/zip/sluc138 

    Regards

    Tom

  • 0 in reply to ThomasCosby
    Expert 1285 points

    Hi Tom

       In the application supplied by ti web site, most of them just talk about how to determine OR get the chemistry ID, few of them mentions about the re-check the accuracy of the chemistry ID... I mean that if i can easily try to check the accuracy by the pulse load or others etc..

      By the way, Qmax is always a bit higher than the FCC value I want to re-check the Qmax myself. How can i get the DOD and Passedcharge..

    Best regards

    Jason Chen

  • 0 in reply to J.C Chen
    TI__Guru 73830 points

    Jason,

    We normally check the accuracy of the chemistry data by looking at the accuracy of the gas gauging functions during charge and discharge. Our evaluation software tools will export the passed charge, but DOD is not a parameter that we export.

    Is your gas gauging function reporting not working properly?

    Regards

    Tom

  • 0 in reply to ThomasCosby
    Expert 1285 points

    Hi Tom

        In my work, Several project use the Polymer lithium cells and these chemistry ID are unknown, so I must do it every time..If instrument is required within 1mV or 1mA, but these instruments are out of these ranges. Especially the accuracy of the charger is 10mV.  So i must re-check the chemistry ID compatibly..

      As above, I must know how the re-check the compatibly..If further, I should know what the relationship between the Qmax and Ra-table based on a typical ID.

    By the way, can you help me to adjust the accuracy to 1mv by a typical electrocircuit ro peripheral component??

  • 0 in reply to J.C Chen
    TI__Genius 14985 points

    You can use something like the bq27520EVM to log the current and voltage while you perform the relax-discharge-relax cycle.  Then the Mathcad tool can be used to process the log file for chemistry selection.

  • 0 in reply to ThomasCosby
    Prodigy 30 points

    The file seems corrupted. Can someone fix that?