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BQ27520-G4: GPC tool, question regarding data collection

Johannes Westman
Prodigy 70 points
Part Number: BQ27520-G4
Other Parts Discussed in Thread: GPCCHEM, BQ25898

Hi,

I've run the relax / discharge / relax cycle on my battery, submitted the data and gotten a response from TI. However, when I ran the tests I did not do so consecutively. I did the relax cycle first, did some other work, and then I left the discharge/relax cycle to be finished overnight at the office as I went home. I then took the discharge/relax log file and just copy pasted the lines to the end of the first file. The data processing seems to have gone fine, however, the error is 7 %. I was wondering whether that really is due to my battery needing to be profiled by TI or if it is because I didn't do the tests back-to-back?

Note that the 'sample' goes up to 213 and then starts from 1 again as I started the second test. Does this matter?

1321.roomtemp_rel_dis_rel.csv

  • 0
    TI__Guru** 102605 points

    Hello Johannes,

    I took a look through the logged data, can you share the package you sent to the GPCCHEM tool? It looks like your current discharge was not constant current, also there's a discrepancy between the instantaneous current and average current, but I'm not sure if that's from the log splicing you mentioned. 

    7% is too high for a match, we usually like to see it 3% or under. 

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi Wyatt,

    Please find the zipped package attached. I'm plugging my custom board into a constant DC load - it seems like the current drops off when the battery is starting to reach full or empty - I assumed this was some property of the gauge? Or perhaps it is my bq25898.

     chemtest.zip

  • +1 in reply to Johannes Westman
    TI__Guru** 102605 points

    Hello Johannes,

    I'm not sure why the current changes near end of discharge, if the system output is through SYS of the charger and there's not power on VBUS the current should be completely dependent on the battery characteristics and your DC load.

    I would try again with a constant current discharge, I believe the current variation near the end is making it challenging for the tool to correlate the voltage with DOD.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi Wyatt,

    I will look into it and try again, thanks.