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BQ20Z95: possibility to read out QPC, DOD, Grid number etc?

Imre Sunyi
Prodigy 110 points

Part Number: BQ20Z95

Hello TI

We are struggling to understand why the FCC (register 0x16) sometimes reports 0 together with SOC (register 0x0d) reporting 0 although the cell voltage is nearly on full level. The max error (register 0x0c) is '1'.

This happens when the battery pack is put in temperature chamber and going from room temperature to subzero temperatures with no load on battery. (Battery pack is operational down to -40 degree C with a maximum discharge of C/8)

Our vendor for the battery pack with built-in bq20z95 gauge claims that the parameters are correct.

We would like to log different kinds of parameters meanwhile the battery pack is subject for cooling down do subzero temperatures.

In the technical reference (sluu264a) there is not much to get in terms of which resistance grid is used, the DOD when OCV is measured, the time since OCV was measured and updated Qstart and so on.

Are there some undocumentet registers available to be able to read out such parameters?

  • 0
    TI__Mastermind 42535 points
    Sorry, we don't have such registers. The battery capacity degrades rapidly at very low temperatures. Even if your chemistry parameters are correct, there may be a temperature dependency to the battery capacity. Also, in our newer gauges we have a PRES pin which detects pack insertion. If your pack is removed from the system FCC can drop to 0.
  • 0 in reply to Batt
    Prodigy 110 points

    I am aware of the temperature dependency to the battery capacity. The rated capacity of the battery is 5.6 Ah at C/5 +25 deg C. At C/5 -40 deg C the capacity is rated to 3.2 Ah.

    The gauge is built-in to the battery pack and the NR is '1' in Operation Cfg B.

    The Load Mode is '1' and Load Select is '2'. That is it is the instant power that determines the FCC calculation at end of discharge.

    When FCC and SOC is '0' at such subzero temperatures, and voltage on nearly full level, I start to discharge the battery with C/8. At a point where I suspect a new resistance grid is selected the FCC and SOC suddenly takes on a value that is not zero. FCC at that time is still much lower than the rated 3.2Ah at that temperature. Same with SOC. As I continue to discharge, the FCC increases at certain levels which I suspect is another grid passing.

    What could bring the FCC and SOC to '0' when voltage is near on full level and there is no discharge when temperature is decreasing below subzero Celcius degrees?

  • 0 in reply to Imre Sunyi
    TI__Mastermind 42535 points
    The bq20z95 resimulates capacity for every 5C change in temperature. It also uses the load curve depending on what you selected in load select. Therefore if your load is high and your temperature drop is also high, it is possible that if your capacity simulations can give you a zero remaining capacity. However, I can't be sure until I see your gg file. Please attach it here so that I can take a look.
  • 0 in reply to Batt
    Prodigy 110 points

    Attached is bq20z95.xlsx. I do not have a .gg file. It is this .xlsx file I got when I asked for reviewing the parameters from our battery pack vendor.

    Let me point out again: The only load applied on the battery is approx 200 uA when subject for temperature decrement in temperature chamber.

    The device this battery pack is residing in has been put on load test (peak is max 1.8C) in temperature chamber set to +50 degC. When that test was done battery was charged to full and device turned off. Before turning off the FCC and SOC reported normal values. Then temperature chamber was set to -40 degC. When powering on the device again the day after the FCC and SOC reported 0.

    bq20z95.xlsx

  • 0 in reply to Imre Sunyi
    TI__Mastermind 42535 points
    Imre,

    You need to get the .gg file because I have no parameters like Ra, chemistry or anything else that can help me deduce this. I need your log file for the dsg and your gg file and your srec or senc firmware to help you.

    It may also be that your chem ID is not adequately temperature compensated. This is another procedure that changes resistance parameters that are temperature dependent. Please use this tool to optimize your battery pack, http://www.ti.com/tool/GPCRB for low temp use.
  • 0 in reply to Batt
    Prodigy 110 points

    Hello

    I asked our battery pack vendor for the .gg file and the srec or senc file but got the .dfi file instead.

    Is that enough for you for analysis?

     

    Br

    Imre

    Golden-file-image_70248E_V1.1.dfi.zip

  • 0 in reply to Imre Sunyi
    TI__Mastermind 42535 points
    Hi Imre,

    I can't really help you without getting the srec or senc files. DFI doesn't provide me all the parameters I need.