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BQ78350 - Setting CEDV config for known chemistry (431) (bqStudio)

Michal Radziwon0
Prodigy 145 points
Other Parts Discussed in Thread: BQSTUDIO, BQ78350

Deal fellows,

I have encountered a problem while designing BMS for 8s20Ah  LiFePO cells from Tenergy.

I have updated the chemistry in device flash (for 431), but CEDV cfg parameters has not changed and remain at default values fitting Li-Po battery. What is more, in chemistry tab of bqStudio, under "Update chemistry in data flash" button, there is text stating "Cemistry Version : 369"; and it remains like that after successful chemistry update.

I can read CHEM_ID from bq78350 and it is 0x0431.

Is there a way to obtain CEDV Cfg parameters from chemistry data, or it is always required to perform experiments at various loads and various conditions to determine them?

Last but not least - the "uptate chemistry" command from help menu does not work - is there any particular reason for it?

  • 0
    Intellectual 795 points
    I was able to load a new Chemistry from TI's list without issues by just following the flow that that software takes you through.

    You might need to refresh your data, or restart the BQ Software to see the fuel gauge data refresh correction in BQStudio.
  • 0 in reply to Ryan Brown2
    Prodigy 145 points
    What do you mean by "the flow that that software takes you through"? I just go to <<chemistry>> tab, choose chemistry and press "update chemistry". After a moment, a confirmation dialog appears, and reading chemistry from bq78350 gives correct number.
    However, CEDV Cfg settings are still as they were - default ones.
    Therefore my main question is - how to get CEDV Cfg parameters of battery listed in chemistry tab?
  • 0 in reply to Michal Radziwon0
    Intellectual 795 points

    I was just saying that I went through the exact same process you did and got the successful confirmation. 

    I would make sure that BQ Software is properly refreshing that data its displaying. Sometimes hitting Refresh at the top right of the Datamemory window does not bring up the updated Flash data. Like when I was trying to see the most up to data info from the Lifetime Section, I had to hit the LT Flush tab on the far right and then refresh the DataMemory window to see the latest info. 

  • 0 in reply to Ryan Brown2
    TI__Guru 54715 points

    The latest bqStudio version is recommended as is the v0_06 build 16 code from the website or recent sample parts.  If you have older versions from earlier development or samples which have been waiting a long time for the project to start we certainly recommend you update.  Chemistry loading as Ryan indicated should work with bqStudio.

    Unfortunately there is not a database of CEDV parameters.  The right way to get CEDV parameters is to collect the data and run through the CEDV calculator on the web.  For faster development consider using a fixed EDV setting which may be more easily estimated from the cell data and load.

  • 0 in reply to WM5295
    Prodigy 145 points

    Thank you for reply.

    I am using the latest bqStudio, and latest firmware for bq78350. Chemistry loading seems to work ( I am getting correct chemID after chemistry change), however, flash memory settings regarding CEDV are not changing at all (even after refreshing).

    The key point is that I understand from your answer, that I still need to do discharging experiments at various conditions to characterize my battery. 

    Could you enlighten me why this is required for battery of cells known to bqStudio?  If I will once characterize a battery, can I use the same CEDV paramters for other batteries of the same structure (8s1p) made of the same cells from the same producer (assuming no major differences will happen in cell production)?


    Best regards,

    Mike

  • 0 in reply to Michal Radziwon0
    Intellectual 795 points

    Mike are you talking about the text box that says Lion? 

    In the same section that shows Manufacturer Name and Date? 

  • 0 in reply to Michal Radziwon0
    TI__Guru 54715 points

    The bq78350 is a CEDV based gauge with the added feature of estimating the state of charge at reset based on the chemistry data.  See the TRM section 8.1.5.  Loading the chemistry does not change the CEDV parameters, these still need to be set for the cells.  Impedance Track gauges get their information for gauging from the chemistry and battery behavior.  Classic CEDV gauges get their information for gauging from the passed charge and loaded CEDV parameters.  The bq78350 part uses both the chemistry for the reset estimate and the loaded CEDV parameters, but changing one does not change the other.

    Once you characterize the pack and determine the CEDV parameters, these should remain the same unless there is some supply disruption or product change as you indicate.  Changing the load or temperature of the application may also change the CEDV parameters, so if you use the 8s1p pack in a new application you should evaluate if the parameters still provide suitable performance or if a new characterization collection & parameter calculation is needed.