BQ34Z100-G1: Non-linear SoC jumps, Vbatt 11-13.29 = SoC 0%, Vbatt 13.3 = 51%

Hello Padam,

Can you provide a log file and .gg file of the tests so we can look at the registers during the cycle and know your configuration?

Sincerely,

Wyatt Keller

Hi Wyatt,

Attached are the last files to and from TI GPC server.

Padam 

gg.csvlowtemp.csvApril12_Charge_13.8VDC.zipApril12_Charge_13.8VDC-report.zip

Hello Padam,

The only way to prevent this would be to lower the terminate voltage for this device and see if the battery can warm back up.

We don't handle frozen batteries too well, especially when the impedance is low.

There are other devices that will hold the RSOC up for seconds, however, this is more of a "work-around" for cells that may not really have any capacity.

We define 0% as soon as voltage is below terminate voltage settings.

Thanks!

Hi Kang,

I understand the mechanism why SoC goes to 0%. I am trying to understand why FuelGauge does not comeback to non-zero SoC upon receipt of RESET x41 command.

Qsns

1. Is it normal for BQ34Z100-G1 to report 0% SoC when battery voltage is 11.1-13.2 and RESET x41 command is sent?

2. Is there anything in my gg.csv files that explains SoC recovery to 51% only when battery voltage is 13.3V? What's the reason for SoC 0% between 11.1V to 13.29V?

3. Isn't RESET x41 same as cold start after which FuelGauge is expected to put highest weight on battery terminal voltage initially? 

Thanks

Padam

Hello Padam,

1. This can be quite normal. It depends on the voltage you sent the reset at. The gauge will predict at that voltage, the IR drop and if we will still have capacity remaining.

2. Did you run a full learning cycle?

3. This is true if the battery cell is well-relaxed.

Thanks!

Hi, Padam

    Could you give some explain with the charger set to 13.33v with Ibat = 0, how the voltage of the battery stack, i.e., per my understanding is Vbat is maintained at the same voltage of Charger, like 13.33v, was the battery charged to this voltage before the charger is applied?

    Do you mean you removed the battery stack and apply the charger to bat input?

Hi Steven,

If you are wondering why Ibat=0  it is mainly because temperature is -35C and battery does not accept charge. Charger was applied to clear ambiguity that relax voltage isn't stable enough.

Below are the sequence of events

1. Battery and charger are part of my system. They are integrated so no manual connect/disconnect required

2. For test, battery is fully charged at room temp up to 13.8V. 

3. Battery and whole system is subjected to -35C for 4hrs

4. Charger is removed at -35C to simulate power loss. System has to run on battery power.

5. Due to periodic 2A load at -35C for 300ms , battery voltage briefly dips to 10.5V and immediately bounces back to 12.8V. Temporary drop below 11V (0 SoC threshold) causes abrupt SoC drop from 90% to 0%. I understand this phenomenon related to internal resistance increase in battery and lack of Vbat filtering on BQ34Z100.

6. To mitigate this, I send RESET 0x41 command at Vbat 12.8V. SoC remains at 0%. Tried different relax interval & RESET command got same result. 

7. I apply charger voltage 13.2V and RESET 0x41 command when Vbat = 13.2 & Ibat =0, SoC remains at 0%.

8. Only time I see change is when charger voltage = Vbat = 13.33V & RESET 0x41 command, SoC jumps to 51%

Qsns

1. If my SoC threshold is set to 11V, why can't I recover to non-zero SoC after sending RESET x41 at Vbat =11.1V-13.2V?

2. What causes non-linear SoC jump from 0 to 51%? Any clues from files sent a week ago?

Regards,

Padam

Hi, Padam

    If 0 soc after reset is caused by the brief dip of cell voltage, then a dataflash item might be changed accordingly, have you checked the dataflash item: Gas Gauging->State->Cell Delta Voltage after you discharged the battery with pulsating load under low temperature?

    The bigger the Cell Delta Voltage is, the more conservative would the gauge be when it performs the simulation to get the RSOC.

    If the issue is caused by the big delta voltage caused by the pulsating load, you may have to consider a hardware method to smooth the battery voltage when pulsating load occurs.

    If the Delta Voltage is not very big, like only 10mv or so, then the issue could be caused by bad low temperature modelling data, you may need to do RbTweak per the guidelines on the TI website:""