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BQ40Z80: During discharge process SoC dropped suddenly from 50 to 0%, Remaining Capacity (mAh) dropped to zero and Full Charge Capacity dropped

Vuk Obradovic
Prodigy 10 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: BQSTUDIO

Several times on different system we had state f charge drop situation occurring randomly:

System uses BQ40Z80 chip to monitor state of charge of 4S LiPo 14.8V 4000mAh battery.

Typical discharge current is in range 14A-16A.

During regular system operation BQ40Z80 reported sudden drop of SOC to 0%. Usually from some higher soc in range 30-50%.

On our master system connected to BQ chip we started collecting additional data from device to try locating issue once situation occurs again.

We managed to catch situation once in field and extracted following info:

1. At the time of drop both current and voltage measurements reported by BQ chip were in regular range, no sudden spikes or any abnormality

2. Drop was detected in following measurements

- SOC dropped from 38 to 0%

- Remaining Capacity (mAh) from 1488 to 0mAh

- Full Charge Capacity (mAh) from 3696 to 2206mAh

We observed same data during charging process afterwards. Remaining Capacity was rising slowly and once it reached Full Charge Capacity both measurements jumped to value of 3692mAh when BatteryStatus reported FC.

Additional info: Typical operation cycle of system:

1. System charged to 100% and remains on charging circuit (no battery drawn from battery)

2. System in use - discharge with aroung 14-16A

3. System in use - waiting for charge to start - discharge with current of around 500mA

4. System charging to full.

Some configuration info:
IT Gauging Configuration: 0xD1CE

IT Gauging Ext: 0x001A

We are also considering to gather gauging data as well such as GaugingStatus() flags and some of GaugingStatus1,2,3 measurements such as compensated resistance and Qmax measurements.

 

  • 0
    TI__Guru** 104905 points

    Hello Vuk,

    Are you able to capture BQStudio logs of this behavior? Can you also share the .gg file with all your settings from the golden image as well as the gauge which is seeing the SOC jump.

    Generally when FCC changes quickly it is due to the gauge re-running a simulation based on the DOD at EOC point which occurs during Valid Charge Termination, the temperature changing to colder value, or load varying significantly so the gauge uses a higher current than it should for the load select setting.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 10 points

    Hi Wyatt, 

    No we didn't manage to reproduce it in controlled environment or in lab with BQStudio attached. Situation is not so often and reproducible.

    Usually our systems don't log details like gauging data and full charge capacity, we plan to enable it for next batch but it might take time before we catch this data in field again.

    Data I presented above is from one system we had in office where we gathered those data and we were lucky enough to catch it in bad state.

    Let me give you more data we gathered from that:

    - Once we got system into state that soc drops suddenly it was happening every time when soc went bellow 50%

    - Full charge restored FCC estimation

    - If system was not fully charged and used again (discharged) SOC drop occurred again at 50% and FCC dropped to 1896mAh

    - We accidentally managed to remove problem with following action: after system was discharged bellow 50% we completely shut it down (usually this doesn't happen in field, system is running all the time), after few minutes we powered it externally (not using battery) and then charged it to full. After this event we were not able to reproduce SOC drop anymore and since then we are successfully using it in range of 20-100%. This pointed out us in direction that problem might be in gauging.

    Here is config we upload to data flash of BQ devices.

    current configBQ40Z80.csv

    Regards,

    Vuk

  • 0 in reply to Vuk Obradovic
    TI__Guru** 104905 points

    Hello Vuk,

    It will not be possible to determine the root cause without more data showing what state the gauge is in. There are multiple different possibilities that can cause FCC to change. As mentioned above there are some common reasons why FCC changes, if a full charge recovers the issue you may have gotten a bad VCT condition at one point which will reduce the FCC, your load select should keep FCC fairly consistent. If you have a pack showing the issue make sure to pull the .gg file while the issue is occurring and if possible a short BQStudio log before and after resolving the issue so we can see all the registers.

    Sincerely,

    Wyatt Keller