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RSOC drop at the begining of discharge in BQ78PL116 (or BQ78PL114)

Ran Aloni
Expert 2386 points

HI all

I'm currently testing the BQ78PL116EVM on a 24V12Ah LiFePO4 Battery.

I chose a chemistry that was close enough to the manufacturer, I use the 415 CHEM file, and created an AUX file for my pack.

I encountered a problem when performing cycling.

 

when I'm discharging, the RSOC starts with a massive drop (from 100% to ~70%), then decline in a linear manner till reaching 0% - prematurely.

 

have anyone encountered this problem?

what is wrong with my system?

do you need any more information?

 

thanks for any help,

this is holding my production.

  • 0
    TI__Intellectual 1940 points

    What was your discharge rate?

    Please feel free in the future to submit a log file from your tests.  This gives the best opportunity to troubleshoot.  You can use the same .dlog configuration file that was used for your .aux file test.

  • 0 in reply to Jim M15252
    Expert 2386 points

    thanks for the reply.

     

    we had a holiday... :-)

     

    1. my discharge rate was 6 A , while C = 12Ah
    2. I will create a log file that documents the event by tomorrow.
    3. here is the log file from which I invoked the AUX file.
      4466.24V12Ah_AUX12.zip

    thanks

  • 0 in reply to Ran Aloni
    Expert 2386 points

    Hi again,

     

    I attaching the log file, it's a bit long, it has 2 cycles on it.

    5700.24V12Ah_AUX13.zip

     

    at the first charge you can see the RSOC "kicking in" very late (starting to rise after about an hour) thus jumping at the end from ~80% to 100%.

    on discharge you can see a drop of 25% on start, an then reaching 0% prematurely.

     

    few things I have in mind:

    1. I changed the capacity algorithm to average current instead of present current - maybe the time when the battery is idle is damaging the measuring?
    2. maybe a more suitable CHEM is in order, I chose the most suitable chem file, I assume TI updates the CHEM file database all the time but how can I update it?
    3. do I have to make sure the system "hits" relaxation mode between every charge/discharge ?

    thank you for bearing with me!

    I will appreciate any help

  • 0
    Prodigy 40 points

    Hi , Ran Aloni 

    I'm a begginner using TI gas gauge.  I would like to test a battery pack, 8S1P 12Ah LiFePO4 battery,using bq78PL116EVM just like you, but I have no idea that how to choose the chemestry ID.Could you provide me your detail procedure for choose chemistry ID?

    Thanks!

    Fred

     

  • 0 in reply to Fred Chang
    Expert 2386 points

    Hi Fred,

     

    there is this application note: <http://focus.ti.com/lit/an/slua372r/slua372r.pdf>

    you need to make specific tests and plot a CSV file or similar.

    I found it kind of hard to implement with out a programmable power supply or analyzer.

    this is what I do:

    I have the BQ27541EVM and EV2300, which is  only a gas gauge chip by TI, this chip comes with BQeazy software from TI.

    part of its startup wizard pages, does a test for chemistry selection, and does that using a simple switching circuit.

    at the end of the test it comes out with the best suitable known chemistry by TI,

    under 3% match is an acceptable match.

    hope I helped.