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BQ40Z60: GPCCHEM and GPCRA0 return "DOD is less than 90%" and "Voltage under load 2786 mV is higher than OCV 2698mV" with LTO cell

Part Number: BQ40Z60
Other Parts Discussed in Thread: GPCRA0, GPCCHEM

Using a custom PCB based upon the BQ40Z60 evaluation board.

2S LTO 1865 1400mAh configuration.

I have tried both GPCCHEM and GPCRA0 methods over a 480mA charge and 160mA discharge with multiple hours of rest before and after each step.

ChemID 700

Target charge current is 500mA and an avg discharge of 60mA

A charge/discharge cycle looks like;

This seems to be > 90% DOD. It tallies at -3.5mAh (max 1373mA) and 27cW (max 355cW) for a single cell.

I am using the CUVC protection as my min stop for the cycles at 1800mV with a 2400mV recovery

Attaching other files below

  • Data log of two full cycles using the BQ chip. temp, voltage and current all calibrated

    data_log_500mA chg_160mA_discharge.zip

  • Hi Lucas,
    For chem id identification you need c/10. Your battery capacity is 1400, so you need 140mA discharge current. how did you get chem id 700?

    thanks
    Onyx
  • You got me there. I've reset my current back to 140mA and will repeat the cycles again.

    There are only two Li titrinate cell types to select from so I selected the first one in the list. If I re-run this at 140mA then GPCCHEM will work?

    How accurate must the 140mA be? +-5mA? +-1mA?

    Should I actually run the full low, room and high temp sequences?
  • +-5mA should be ok. If you rerun using 140mA, make sure to charge to the max voltage specified in the battery data sheet and discharge to the minimum voltage as well. GPCchem would work as long as you followed the instructions.

    thanks
    Onyx
  • Ah gees now who feels silly :) What about the GPCRA0 utility? That complains heavily about the OCV being lower than the voltage under load. Is it not incorrectly calculating the OCV? Am I going to get the same result using Chem 700 as I did just then?

    The ChemID tool will only tell me the chem to use, not the initial Ra[0..14] ??

    I just tried "scaling" my data to 140mA (yes I know this is wrong.. ) and it spat out Chem ID 700

    Chemistry ID selection tool, rev=2.24		
    		
    Configuration used in present fit:		
    ProcessingType=2		
    NumCellSeries=1		
    ElapsedTimeColumn=0		
    VoltageColumn=3		
    CurrentColumn=1		
    TemperatureColumn=2		
    		
    Best chemical ID : 700	Best chemical ID max. deviation, % : 74.08	
    		
    		
    		
    Summary of all IDs with max. DOD deviation below 3%		
    		
    Chem ID	max DOD error, %	Max R deviation, ratio
    0	0	0
    		
    Accuracy Error: 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		
    		
    		
    Selection of best generic ID for ROM based devices like bq274xx		
    		
    		
    Device / Family #1		
    Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
    312	bq27421-G1B: 4.3V LiCoO2	100
    354	bq27411-G1C: 4.35V LiCoO2	100
    3142	bq27421-G1D: 4.4V LiCoO2	100
    128	bq27421-G1A: 4.2V LiCoO2	200
    Best generic ID 312		
    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	100
    354	bq27621:  (ALT_CHEM2) 4.35V LiCoO2	100
    1202	bq27621: (default) 4.2V LiCoO2	197.5
    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, %
    3230	bq27426: (default) 4.35V LiCoO2	100
    3142	bq27426: (ALT-CHEM2) 4.4V LiCoO2	100
    1202	bq27426: (ALT_CHEM1) 4.2V LiCoO2	197.5
    Best generic ID 3230		
    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		
    		
    		
    Warning: difference between initial and final DOD is less than 90% dDOD_%=  40 Try to decrease the discharge rate		
    Warning: difference between initial and final DOD is less than 90% dDOD_%=  40 Try to decrease the discharge rate	

  • Can you explain what you mean by you just tried scaling your data? You can't subtract or divide the current if that is what you are doing because the voltage response of the battery is tied to the current drawn from it. As you can see, even though the tool is returning chem id 700, you see the max deviation is 74%. That is not a match. The max deviation should be less than 3%.

    thanks
    Onyx
  • I just "cheated" by making the time longer on the discharge to scale the current over time to see what it would output. Obviously this is by no means a good idea. I was curious about how your tool calculate the max capacity and what it was looking for that's all.. Seeing as I had two chem choices (700 or 701) for lithium titanate was I was logging data for the GPCRA0 tool

    My test unit is 25% through the discharge phase now so I'm awaiting the completion and rest times. I did set the chem type to 701, the only other choice, and oddly, or correctly I achieved a QMAX update at full charge. Max error reports at 3% and I have an update status "ITEN | CF0" in ITSTATUS.. which is a good thing.

    The discharge is reporting +NSFM, +RDIS and -VDQ .. not sure if this is a good sign but I hope the output from this can be used in the RA0 tool. This will at least get me started in the right direction.

  • Ok I've re-run this with 142-137mA and I'm getting the same kind of wild reports.

    Trial 3.zipTrial 3-report.zipCell 1-report.zipCell 2-report.zipCell 1.zipCell 2.zip

    0
    Warning: difference between initial and final DOD is less than 90% dDOD_%= 0 Try to decrease the discharge rate
    Warning: difference between initial and final DOD is less than 90% dDOD_%= 0 Try to decrease the discharge rate

    0 0 0
    Warning: DODdifference before and after discharge less than 70% Qmax accuracy reduced: 0 0
    Warning: Voltage under load 2827 mV is higher than OCV -9867mV. Please check correctness of your chem ID. 0 0
    Warning: DODdifference before and after discharge less than 70% Qmax accuracy reduced: 0 0
    Warning: Voltage under load 2827 mV is higher than OCV -9867mV. Please check correctness of your chem ID. 0 0

    0 0 0
    Warning: DODdifference before and after discharge less than 70% Qmax accuracy reduced: 0 0
    Warning: Voltage under load 2838 mV is higher than OCV -84mV. Please check correctness of your chem ID. 0 0
    Warning: DODdifference before and after discharge less than 70% Qmax accuracy reduced: 0 0
    Warning: Voltage under load 2838 mV is higher than OCV -84mV. Please check correctness of your chem ID. 0 0

    Raw datalog attached below

    trial 3 raw datalog.zip

  • I've upped the charge current to 1400mA and now the device is starting to respond. I've had one Ra update and two QMAX updates and I now have an updated Ra table and a Max Error of 1% as of this morning.

    I'll re-process the last data logs and submit them again and see if the tools calculate a result. The device is reporting VDQ, QMAX through the cycles now without disabling after swapping to the 701 chemistry ID.

    One of the resistance numbers updated this morning from 32mOhm to 224mOhm. This is the value calculated from Ra_0 through Ra_12 there about..

    So looking better now :)