BQ40Z80: use new battery cell

Part Number: BQ40Z80
Other Parts Discussed in Thread: BQSTUDIO, GPCCHEM, EV2400

Hi,

Previously i used the 3000mAh batteries cell with BQ40z80.

Now i am using the new 4000mAh batteries. However i still see Qmax 3150mAh on the bsq.

Also, the SOC is 7% with 25.2V battery. I think the SOC is incorrect (SOC should be higher for this 25.2V). Please refer to attached figure.

What do i need to do after programming the correct chemistry ID to the BQ40Z80 (Battery ID 5441)? Do i need to do calibration or learning cycle for new battery on BQ40Z80 so that to get correct SOC?

Thanks!

  • Hi KIM,

    You will need to run another learning cycle for the new batteries. Calibration could help as well if the voltage and/or current readings are off.

    Best,

    Jessica

  • Hi,

    Is this learning cycle on new battery required to do for all battery pack?

    Or we can do it one time and copy the data to another battery pack?

    We will have production on the battery pack. Just wonder we need to do this learning cycle for all the battery pack in production.

    Thanks,

    Kim

  • Hi Kim,

    You will only need to do a learning cycle on one battery pack. After doing that you can create a new golden image and program the other gauges using the 4000mAh batteries.

    Best,

    Jessica

  • Hi Jessica,

    Can you provide the guideline to create the golden image? or any document to refer?

    Thanks,

    Kim

  • Hello Kim,

    SLUA903 is a good reference for the learning cycle: https://www.tij.co.jp/jp/lit/pdf/slua903

    Also SLUA848: https://www.ti.com/lit/pdf/slua848

    To export the golden image .srec file, you can use BQStudio -> firmware -> read srec.

    There's not really a guide to create the golden file, once you find your chemistry ID with GPCCHEM and complete a learning cycle using the guides above, you configure and application specific registers and export the golden image.

    Sincerely,

    Wyatt Keller

  • Hi,

    The 1st step is to discharge the battery to empty. Based on the guideline, the LStatus() is 0x04 after full discharge. But the LStatus() for my case is 0x06. Please see the attachment.

    Should i proceed to next step (charge the battery to full)?

    Thanks!

  • Hi Kim,

    It is likely that the 0x06 is leftover from the previous learning cycle for the old battery. Please set Update Status back to 0x00 and try again.

    Best,

    Jessica

  • Hi,

    i am using INR21700-40T (7 in series). 

    the data sheet mentioned the standard discharge capacity is 4000mAh. 

    what is the nominal capacity in Ah and cWh I should use in learning cycle for this battery?

  • Hello Kim,

    You should use the 4000mAh rating. The cWh is the nominal voltage multiplied by the mAh rating and  divided by 10. So cWh = (3.6V*4000mA)*(centi/10mili) = 1440cWh.

    Sincerely,

    Wyatt Keller

  • Hi,

    The battery connection is 7 in series.

    For cwh, i think it should be 1440cWh * 7 = 10,080 cWh.

    Please confirm if i should use 10,080 or 1440 cWh for 7 batteries in series.

    Thanks!

  • Hello Kim,

    Yes it should be based on the stack nominal voltage, my example was for 1S1P.

    Sincerely,

    Wyatt Keller

  • Hi,

    1) Do we need to have constant current discharge (between C/10 and C/5) for the 1st discharge? Or the discharge current value is not important in this step (just discharge the batteries to empty)?

    2) Do we need to use the constant current load for discharge (e.g. C/5) in Step 5?

    For my 4000mAh battery, I am thinking to use the fixed resistor for discharge.

    R=40 ohm, battery voltage variation during discharge is from 29.4V to 21V.

    The discharge current is not fixed, from 735mA (29.4/40) to 525mA (21/40). The current is still within required 0.1C and 0.2C discharge current.

    Can you advise if i can use the fixed resistor for discharge and discharge current is not fixed?

    Thanks!

  • Hello Kim,

    I would recommend using constant current discharge to ensure the learning cycle gets completed with no issues. You will get a better Ra update with constant current discharge.

    Sincerely,

    Wyatt Keller


  • hi, 

    for the first discharge as below, do we need discharge current in between C/5 and C/10? Thx


  • Hi Kim,

    It is not as important to use a discharge current between C/5 and C/10 for the first discharge.

    Best,

    Jessica

  • Hi,

    I did the full charge and have 2 hours rest period.

    The Qmax still remain at 0 instead of 1.

    Can you advise why the Qmax is not updated?

  • Hello Kim,

    If the Qmax didn't update then one of the Qmax update conditions were violated described in the TRM. For the first Qmax you need a 90% change in DOD, other Qmax updates afterward needs atleast 37%.

    Can you share the logs and .gg with us so we can look at possible issue?

    Sincerely,

    Wyatt Keller

  • Hi Wyatt,

    I did not log the data when doing the learning cycle.

    Attachment is the .gg file.1651.BQ40Z80.gg.csv

    Thanks!

  • Hello Kim,

    Without the log data I can only give suggestions of common things that disqualify the learning cycle. Most of the time for Qmax during the learning cycle it's the 90% change in DOD that causes an issue. If the wrong chem ID is uploaded that can occur more easily. You can try updating all the Qmax parameters along with the Design capacity to the battery spec (I believe you said 4000mAh.)

    When you started the learning cycle did you upload a default .srec or did you use your previous applications settings?

    Sincerely,

    Wyatt Keller

  • Hi Wyatt,

    i reuse the previous srec file. I updated the chem ID to 5441 and changed the parameters as per request like design capacity, term voltage, dsg current etc. 

    do we need to use the default srec from TI website to do the learning cycle?

    i will try to update all the Cell Qmax to 4000mAh and redo the learning cycle to see if the Qmax bit be toggled. 

    thanks!

  • Hello Kim,

    Let us know what the results are.

    This can also be due to the BQ40Z80 no longer supporting 7S systems. The log will also help determine this.

    Sincerely,

    Wyatt Keller

  • Hi Wyatt,

    1) What are the data you would like to see in the log?

    We want to know what you mean BQ40Z80 no longer supporting 7S systems.

    We have the 7s BMS with BQ40Z80 developed few years back for certain battery cells.

    2) Can the developed 7s BMS board work properly if we use new manufactured BQ40Z80 chip and program the previous golden image to the new BQ40Z80?

    3) Is there any issue if we want to use the developed 7s BMS board for new battery cells? Can the new manufactured BQ40Z80 chip be used for 7s learning cycle with previous application setting?

    Thanks!

     

  • Hello Kim,

    The log should be using bqStudio if possible using the EV2400, it will automatically log all the registers we have access to. You can check the WDT reset counter also, if it keeps incrementing during your tests this can cause issues.

    How was the original learning cycle completed? The 7S support was dropped due to some issues with internal protections and FW. With 6S this is not an issue.

    Sincerely,

    Wyatt Keller

  • Hi Wyatt,

    Where can i check the WDT reset counter? Thanks!

  • Hello Kim,

    I can check for you, can you send me the .srec pulled before and after your test? 

    Sincerely,

    Wyatt Keller

  • Hi Wyatt,

    We have changed Qmax of each cell to 4000mAh. We are able to get Qmax updated and LStatus is 0x06 after the full charging and full discharging cycle. Please refer to attached figures.

    From App note,

    When the packs are deployed in the end equipment and a field update occurs, the LStatus() updates to 0x0E, which means that cell balancing has been enabled. If an LStatus() of 0E is not obtained, the device can be charged to full, relaxed for 2 hours and then discharged to empty, at which point it should be 0E.

    Do we need to enable the cell balancing (set CB bit) before we do another round of charge and discharge to have LStatus = 0x0E? Or the field update = 1 mean the cell balancing is working?

    If we need to do another round of charge and discharge, use C/2 for charging and C/5 for discharging?

    Thanks! 

  • Hello Kim,

    The field Qmax update has a lower requirement for DOD change between rest periods. You must have 37% change in DOD for field Qmax, you need 90% for learning cycle.

    One more cycle with should allow the update to 0X0E, once the learning is completed you will also need to enable the CB bit, you can leave it enabled the whole time, it just won't balance until the 0x0E status. C/2 charge and C/5 discharge is fine for the field Qmax update.

    Sincerely,

    Wyatt Keller

  • Hi Wyatt,

    We have done another round of charge and discharge. LStatus() is 0x14 instead of 0x0E. Please refer to attached figure.

    1) Any reason LStatus() is 0x14? 

    2) notice both relative SOC and absolute SOC are 0% but the cell voltage is about 3.03V (BATT is 21.355V). I believe the SOC should not be 0% when the BATT is 21V++ (cell voltage is 3V++). Any thought?  

    Thanks!

  • Hello Kim,

    That value reported in the register tab is in decimal, you can check the data memory tab -> gas gauging -> update status for the actual value in hex.

    14 decimal indicates 0x0E which is fully learned.

    Was the gauge_en command just sent? It looks like the ITEN bit is black which indicates it changed on the last refresh. It will take a few seconds for the values to update then you must refresh the page again. You may need to issue a reset command to force an OCV reading if the batteries are relaxed.

    Sincerely,

    Wyatt Keller