BQ27421-G1: Debug registers address location and definitions that are not in the datasheet or technical reference but are available through Bqstudio.

How do I determine the compatibilities of battery chemistry to the hard coded CHEM_ID of 0x0128? What is the acceptable deviation for this fuel gauge and what are the results if outside the unspecified range?

Our discharge data submission returned the following results:
First submission GPC_report.txt: 2058 Best chemical ID max. deviation, % : 5.15
Second submission GPC_report.txt: 3608 Best chemical ID max. deviation, % : 4.86

In the General Description of the Technical Reference, it states the following, however, it does not state what the discharge profile is for 0x0128 or how to qualify or disqualify it's compatibility to our or other battery chemistries.

“Unlike some other Impedance Track fuel gauges, the bq27421-G1 cannot be programmed with specific battery chemistry profiles. For many battery types and applications, the predefined standard chemistry profiles available in the bq27421-G1A, bq27421-G1B, or bq27421-G1D fuel gauge are sufficient matches from a gauging perspective.”

I was under the impression that after a learning cycle, the golden file with the updated Ra tables would compensate for the differences in battery chemistry and aging.

You note that the "post description" matches a case where the gauge is not a good match to the battery chemistry you are using.  How did you determine the "post description" matches an incompatible case and is that suggesting that our battery is not compatible with this gauge?  Is this determination absolute, or inferred?

Thanks Shirish,

I did not see any reference to BQ27421 or CHEM_ID 0x0128 in the report.

Summary of all IDs with max. DOD deviation below 3%
Chem ID max DOD error, % Max R deviation, ratio
0 0 0
Warning: Deviation is above recommended level. New chem ID needs to be released for this cell. Please contact your TI representative to send the cell to Dallas for characterization

Device / Family #1
Generic Chem ID Device/ Voltage/ Chemistry max DOD error, %
3142 bq27421-G1D: 4.4V LiCoO2 23.75
354 bq27411-G1C: 4.35V LiCoO2 25.29
128 bq27421-G1A: 4.2V LiCoO2 36.14
312 bq27421-G1B: 4.3V LiCoO2 41.54
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, %
354 bq27621: (ALT_CHEM2) 4.35V LiCoO2 25.29
1210 bq27621: (ALT_CHEM1) 4.3V LiCoO2 30.42
1202 bq27621: (default) 4.2V LiCoO2 33.01
Best generic ID 354
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

I have meticulously gone through the video and SLVA725A document and I believe I have the correct headers, columns, units, decimal places, charge/discharge current polarity, config file, and filenames.  Does this data seem valid?

First submission format EV2400 using Bqstudio logging on bench:

Second submission format Maccor with temp chamber set to 30C:

Note: I want to defer the question about the change in load at the end of charge until after I understand the battery chemistry compatibilities, because I believe this may complicate the discussion at this point.

Thanks

Hello David,

The table text does not align correctly. This is the section in the report

3142 bq27421-G1D: 4.4V LiCoO2 23.75
354 bq27411-G1C: 4.35V LiCoO2 25.29
128 bq27421-G1A: 4.2V LiCoO2 36.14
312 bq27421-G1B: 4.3V LiCoO2 41.54

The first format is preferred: seconds,  mV, mA, temperature at 2 decimal places. GPCCHEM tool has some intelligence to detect other units. I would recommend using the first format.

Make sure there are no protectors or other circuits connected to the cell when taking the log.

Shirish,

I am not sure what table text does not align correctly.  If you are referring to the table I cut in, that was from opening in Excel, but the text file is CSV formatted like this in text view:

ElapsedTime,Voltage,AvgCurrent,Temperature
24, 3523, 989,24.25
25, 3525, 989,24.45
28, 3527, 987,24.45

I am assuming carriage return line feeds are acceptable (even though the document showed their data all in line).  Am I missing something in the formatting?  I have the units correct as you stated. Is there any chance there is a representative roomtemp_rel_dis_rel.csv file I can reference that works with the tool?

The section you specified in the report shows an extreme % difference, so I am still not sure if it is valid or not.  I do now see that the target IC is 36.14, I missed that earlier with all the data that seemed too far off.

The protection circuit is built into the battery.  I could cut out the protection circuit, but that would not be how the fuel gauge would see the battery cell.  Wouldn't the protection circuit be part of the evaluation of the battery impedance?  The fuel gauge is on our PCB, so only power and thermistor connection to the battery charger is available.

Thanks

David Nivens

Shirish,

Okay, thanks for clearing that up for me.  So I am assuming that the data formatting is correct and not part of the issue.  We have tested bare cells with the Maccor earlier, but I have not done that with the fuel gauge EV2400 and Bqstudio to get the linear timing that is preferred.  I will work on setting that up early next week and try to resubmit the data by midweek.

I do have a side question on that though.  Should I use the fuel gauge internal temperature for the data since that is included in the Bqstudio log even though the fuel gauge is not in direct contact with the battery, or should I try to align a thermocouple logger data timeline with the timeline of the Bqstudio log data (which will be tricky)?  That was one benefit of the Maccor in that it logged the thermocouple data with the battery data synchronously.

Thanks

Shirish,

Sorry for the delay in responding since I accidently shorted the non-isolated thermocouple to the cell which caused the temp readings to be incorrect when charging and discharging, and I had to re-run the battery cycle again.  The CHEM_ID report seems similar, but without the protection circuitry, there was one CHEM_ID (#5377) was within 3% with a max deviation of 2.96%.  I am not sure what direction to go with this information though.  I am assuming that the current fuel gauge will not be recommended based on this information.  Would a programmable chemistry fuel gauge be recommended, and if so, how would I identify that component?

Here is the full CHEM_ID report:

Chemistry ID selection tool, rev=2.52

Configuration used in present fit:
ProcessingType=2
NumCellSeries=1
ElapsedTimeColumn=0
VoltageColumn=1
CurrentColumn=2
TemperatureColumn=3

Best chemical ID : 5377 Best chemical ID max. deviation, % : 2.96



Summary of all IDs with max. DOD deviation below 3%

Chem ID max DOD error, % Max R deviation, ratio
5377 2.96 1.63
2141 3 1.08

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 19.76
354 bq27411-G1C: 4.35V LiCoO2 21.44
128 bq27421-G1A: 4.2V LiCoO2 28.74
312 bq27421-G1B: 4.3V LiCoO2 32.97
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, %
354 bq27621: (ALT_CHEM2) 4.35V LiCoO2 21.44
1210 bq27621: (ALT_CHEM1) 4.3V LiCoO2 25.82
1202 bq27621: (default) 4.2V LiCoO2 26.6
Best generic ID 354
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 19.76
3230 bq27426: (default) 4.35V LiCoO2 21.77
1202 bq27426: (ALT_CHEM1) 4.2V LiCoO2 26.6
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

Note: I realize due to the Good Friday Holiday, I likely won't get a reply until next week.
Thanks

Shirish,

I have obtained the BQ27510EVM and connected our battery and the EV2400.  Under Chemistry of BQStudio, I was expecting to be able to program in Chemistry number 5377 that was recommended by the CHEM_ID report for our battery, however I do not see that CHEM_ID as an option.  How do I enter the CHEM_ID that's the closest match to our discharge profile within 3%?

Thanks

Shirish,

I apologize for sending that last question too quickly.  I finally figured out how to update the CHEM_ID list and have updated to the Lishen LR2170SD (5000mAh) 5377 LiMn2O4 (Co,Ni)/Carbon, 4.2V battery.  I believe I can now run some battery cycles to see how well it tracks after I program the appropriate registers.

Thanks.

Hello David,

Good to hear that you have made progress. Flowchart for learning cycle is at www.ti.com/.../sluu327b.pdf