BQ34Z100-G1: Chemical ID deviation 13%. Impact on SOC accuracy and SOH accuracy using Lifepo4

Hi Yunfeng,

Can you provide full GPCCHEM report and log file? bq274xx suggestions are ROM gauges, ignore if you don't need. What is the max current in the application, 250 uOhms is too low, you should use the full ADC range as much as possible.

logfile_chimie id.zip

Chemistry ID selection tool, rev=2.5		
		
Configuration used in present fit:		
ProcessingType = 2		
NumCellSeries = 1		
ElapsedTimeColumn=0		
VoltageColumn = 1		
CurrentColumn = 2		
TemperatureColumn = 3		
		
Best chemical ID : 436	Best chemical ID max. deviation, % : 13.78	
		
		
		
Summary of all IDs with max. DOD deviation below 15%		
		
Chem ID	max DOD error, %	Max R deviation, ratio
436	13.78	1.22
421	14.31	0.76
		
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, %
128	bq27421-G1A: 4.2V LiCoO2	1707.38
3142	bq27421-G1D: 4.4V LiCoO2	1844.43
354	bq27411-G1C: 4.35V LiCoO2	1872.32
312	bq27421-G1B: 4.3V LiCoO2	2157.65
Best generic ID 128		
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, %
1202	bq27621: (default) 4.2V LiCoO2	1532.23
1210	bq27621:  (ALT_CHEM1) 4.3V LiCoO2	1599.74
354	bq27621:  (ALT_CHEM2) 4.35V LiCoO2	1872.32
Best generic ID 1202		
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, %
1202	bq27426: (ALT_CHEM1) 4.2V LiCoO2	1532.23
3142	bq27426: (ALT-CHEM2) 4.4V LiCoO2	1844.43
3230	bq27426: (default) 4.35V LiCoO2	2218.33
Best generic ID 1202		
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		
		
		

Thank you abraham, Here are the report and the log file. The cell is a unique 105Ah LifepO4 (a rectangular cell). (Note that the report sends back a 50Ah chem ID...)

The max current in the application is of about 300Ah. The plan was to calibrate the current with a ratio of 1/10 and write in the component memory a capacity of 1/10th of the one we actually have... Do you know the impact on the SOC and SOH accuracy?

Also, there is still this last question that we are wandering about: 

• if we understood well the SLUA450 Document, OCV is the main parameter to define the Ra table and Qmax. After a long shutting of period of our system, When it wakes up, does the bq34z100 give an approximate value of the SOC with only an OCV measurment?

Hello Abraham,

Thanks for these answers. Can I ask for more precisions please? 

I haven't seen anything about SOC and SOH accuracy. Is it because they depend on the Chem ID deviation and the quality of the learning cycles?

-For a proper design we ought to caracterize an accuracy what do you suggest? 

-And we wonder: Every chem ID id represents a table of OCV and Ra0 table when the battery is brand new. Does that mean that, when a battery pack is newly connected to a bq34z100 device, it will give an approximate SOC value by comparing the Voltage taken to the OCV table?

I am sorry for this question, but I haven't seen any statement about it in the slua450

Sincerely,

Yunfeng

"learning cycle is needed to get accurate SOC readings. "

Do you mean that every battery we sell as to be the object of a learning cycle? or only one learning cycle with one battery is enough to make a proper Golden Image and have a precise SOC?