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BQ27520-G4: OCV commands are sent from the host side on a regular basis.

user6092183
Prodigy 200 points
Part Number: BQ27520-G4
Other Parts Discussed in Thread: BQSTUDIO

Hi,

I am developing a device that frequently inserts and removes batteries.
Therefore, the OCV measurement performed when inserting and removing the battery is important.
When measuring OCV, the battery may have poor contact and SOC may not be measured accurately.
For example, as shown in the attached figure, there is an event that SOC cannot be measured accurately even in the same battery.

Therefore, we are considering sending an OCV command every 10 seconds from the host side so that even if a different SOC is acquired, the OCV measurement will be performed again and an accurate SOC will be acquired.
Is there a problem when sending OCV commands from the host side on a regular basis?
For example, RaTable is not updated.

Best Regards,
Shun.

     

  • TI__Expert 3030 points

    Hi Shun,

    OCV readings are OK when battery is relaxing, but it won't be accurate when discharging/charging. Have you tested and made sure it is a HW connection problem? The gauge is measuring the voltage correctly even when SOC is 0%, maybe it is because of a poor Chem ID match.

  • in reply to Abraham Rashid
    Prodigy 200 points


    Hi,Rashid

    I have tested HW connection.
    I have confirmed the reproducibility.
    It has been confirmed that SOC can be measured normally when there is no poor contact, and that the SOC value changes when poor contact occurs.
    I am using CHEM_ID obtained by GPC tool.
    I presume that the voltage is updated every second, but if the SOC value gets an incorrect value in the OCV measurement, that value is retained, so only the voltage can be measured correctly.

    Best Regards,
    Shun.

  • in reply to user6092183
    TI__Expert 3030 points

    Hi Shun,

    How much is the Chem ID deviation reported by GPC tool?

    SOC is calculated every second also, can you connect the gauge to bqStudio and log the data while the issue is replicated? We need the log file for further investigation.

    Best regards,

    Abraham

  • in reply to Abraham Rashid
    Prodigy 200 points

    Hi,Rashid

     Chem ID deviation is % : 2.14
    [File:bat insert check gauge accuracy.log] is the discharge data when the SOC value is not accurate due to poor contact.
    Finally, I have confirmed that the SOC value is updated by the OCV command.

    Best Regards,
    Shun.

    bat insert check gauge accuracy.log

    02308.GPC_report.txt 
    Chemistry ID selection tool, rev=2.5		
		
Configuration used in present fit:		
ProcessingType = 2		
NumCellSeries = 1		
ElapsedTimeColumn = 0		
VoltageColumn = 2		
CurrentColumn = 3		
TemperatureColumn = 1		
		
Best chemical ID : 3608	Best chemical ID max. deviation, % : 2.14	
		
		
		
Summary of all IDs with max. DOD deviation below 3%		
		
Chem ID	max DOD error, %	Max R deviation, ratio
3608	2.14	0.27
2088	2.87	0.47
		
Max. deviations for best ID is within recommended range. Chosen best chemical ID is suitable for programming the gauge.		
		
		
Selection of best generic ID for ROM based devices like bq274xx		
		
		
Device / Family #1		
Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
3142	bq27421-G1D: 4.4V LiCoO2	21.08
354	bq27411-G1C: 4.35V LiCoO2	24.14
128	bq27421-G1A: 4.2V LiCoO2	27.51
312	bq27421-G1B: 4.3V LiCoO2	36.97
Best generic ID 3142		
Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule		
		
		
Device / Family #2		
Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
1210	bq27621:  (ALT_CHEM1) 4.3V LiCoO2	22.36
1202	bq27621: (default) 4.2V LiCoO2	23.17
354	bq27621:  (ALT_CHEM2) 4.35V LiCoO2	24.14
Best generic ID 1210		
Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule		
		
		
Device / Family #3		
Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
3142	bq27426: (ALT-CHEM2) 4.4V LiCoO2	21.08
1202	bq27426: (ALT_CHEM1) 4.2V LiCoO2	23.17
3230	bq27426: (default) 4.35V LiCoO2	24.18
Best generic ID 3142		
Warning: Generic ID Deviation is so high that it is most likely due to anomaly in the data. Please check that data files have recomended format, units and test schedule

  • in reply to user6092183
    TI__Expert 3030 points

    Hi Shun,

    Chem ID deviation looks good, I'll look at the log file and get back to you next week.

  • in reply to Abraham Rashid
    TI__Expert 3030 points

    Hi Shun,

    I looked at the data and it seems SOC is changing along with voltage, see in the image below. So poor connection leaded to inaccurate voltage measurement, which leaded to inaccurate SOC reporting.