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BQ27520-G4: Update Status and Qmax not change during learning cycle

Part Number: BQ27520-G4
Other Parts Discussed in Thread: BQSTUDIO, EV2400, GPCCHEM

Hello,

I'm trying to do the learning cycle of the bq27520g4 on our board (not on EVK) with EV2400 and bqStudio.
I have some questions:

1. While doing the learning cycle, I discharge the battery to 3 V, and after relax the RUP_DIS bit become 0. Then I charge the battery, FC become 1 near the end of charge, but become 0 when there is still charging current. The VOK become 1 during charging and become 0 after 2 hours of relax, but the Qmax in Data Memory not change. Also the Update Status in Data Memory are still 00. This means the learning cycle failed.

Can you help me to find out where is the problem?

The attached file is the registers log during the learning cycle.

learning_log_2.log
I also auto-export the Data memory during learning every 5 minutes. The first exported file is attached. The only change in the subsequent record is "Calibration","Data","CC Offset", "Gas Gauging","State","Cycle Count 0" increasing from 11 to 15, and "Gas Gauging","State","Cell 0 V at Chg Term" change from 4200 mV to 4164 mV.

1learning.gg.csv

2. When I send IT_ENABLE and RESET command, the QEN bit is 0. I think this might because of the BAT_DET bit is 0, so I send the BAT_INSERT command, and the QEN bit becomes 1. Will this affect the learning cycle?

3. When I use the Chemistry tool in bqStudio to program the gauge to certain chemistry ID, only the Chem ID in OCVa1 Table updated to the new chemistry ID. But the LU_PROF in bit registers is 0 during the learning cycle. Does this means that the learning cycle is doing on cell 0 while the correct chemistry ID is set to cell 1 so the learning cycle will fail?

4. Where can I download the default .srec file of this gauge if I want to restart the learning cycle?

Thanks.

Benjamin

  • Hello,

    For Q3, I had found the firmware bundle on the product page, so please skip this question.

    I have another question: The spec of our battery says use 4.2 V charge to current < 0.01 C. On the other hand, our board will stop charging at around 4146 mV and 300 mA. Is this okay for the learning cycle (with taper current set to around 350 mA, slightly large than 300 mA) or should I use an external charger to charge the battery till the current < 0.01 C (60 mA)?

    Thanks.

    Benjamin

  • Hello Benjamin,

    Can you share you GPCCHEM report you received to find your chem ID or the chem ID you are using if you have an exact match battery? Could you also share the full discharge cycle? It looks like the log sent started halfway through a discharge and stopped halfway through the next discharge.

    We need to get at least a 90% change in DOD on the first Qmax update, that means for the given battery voltage range in the chem ID we must have two OCVs taken, one near full charge and one near full discharge. If your taper rate is high it may lead to the battery relaxing to a lower voltage which would prevent you from getting a valid OCV for first Qmax update.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    Thanks for your replying.

    The attatched file is the GPCCHEM report. The max diviation percentage is 8.37%, which seems a little high, and the report chem ID 408 is for a 2200 mAh Li-ion battery while the bettery I use is a 6000 mAh Li-ion polymer battery. But I did the GPC process two times and both of them gave me the same chem ID 408, so I doing the learning cycle with this.

    Whould using the wrong chem ID makes the learning cycle fail? (can't even update the qmax and update status)

    The log I used to uploaded to the GPCCHEM is also attatched. During the log, I use the same board to charge the battery to around 4164 mV, 300 mA. Then I use the system on the board as the load to discharge the battery, the system shutdown at around 3.3 V, so the battery starts to relax.

    3051.GPC_report.txt
    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 : 408	Best chemical ID max. deviation, % : 8.37	
    		
    		
    		
    Summary of all IDs with max. DOD deviation below 15%		
    		
    Chem ID	max DOD error, %	Max R deviation, ratio
    408	8.37	0.68
    283	8.88	0.55
    1237	9.91	0.16
    282	10.65	0.44
    5167	10.68	0.26
    2161	10.92	0.19
    2123	11.01	0.32
    2155	11.27	0.26
    5434	11.37	0.38
    256	11.45	0.34
    508	11.74	0.18
    5590	11.81	0.18
    1181	12.05	0.68
    2150	12.16	0.24
    2348	12.29	0.3
    2133	12.29	0.39
    2782	12.44	0.32
    272	12.47	0.48
    5272	12.5	0.36
    1895	12.51	0.26
    1169	12.51	0.53
    1899	12.55	0.61
    5265	12.55	0.32
    2708	12.58	0.52
    101	12.61	0.4
    3608	12.65	0.4
    2142	12.86	0.45
    2361	12.89	0.35
    2349	13.01	0.31
    2124	13.03	0.45
    2085	13.06	0.27
    1762	13.09	0.28
    2589	13.1	0.29
    2429	13.11	0.28
    2897	13.18	0.39
    5343	13.2	0.39
    5271	13.21	0.41
    5541	13.23	0.99
    2250	13.26	0.47
    5440	13.28	0.33
    112	13.29	0.6
    2137	13.33	0.64
    2046	13.33	0.44
    5442	13.33	0.45
    5377	13.36	0.26
    5153	13.38	0.47
    204	13.44	0.51
    2050	13.44	0.47
    1297	13.46	0.81
    2591	13.5	0.5
    2158	13.53	0.48
    1382	13.58	0.44
    2088	13.59	0.35
    2684	13.59	0.39
    2412	13.59	0.16
    246	13.6	0.31
    1139	13.61	0.8
    2039	13.63	0.48
    2162	13.63	0.49
    5187	13.66	0.32
    2457	13.68	0.52
    5431	13.69	0.3
    241	13.7	0.63
    2144	13.72	0.23
    181	13.73	0.68
    2268	13.75	0.37
    2419	13.83	0.4
    2379	13.92	0.46
    2006	13.92	0.9
    5399	13.96	0.39
    138	13.97	0.44
    229	13.99	0.5
    2068	14.01	0.59
    2098	14.12	0.34
    2149	14.13	0.29
    1203	14.15	0.92
    2555	14.15	0.55
    2796	14.22	0.49
    1857	14.24	0.78
    1151	14.26	0.81
    1211	14.27	0.75
    2152	14.29	0.49
    2111	14.33	0.4
    5106	14.33	0.35
    1254	14.36	0.36
    2396	14.37	0.46
    1171	14.38	0.51
    5247	14.43	0.55
    294	14.44	0.48
    196	14.53	0.75
    2049	14.55	0.49
    1580	14.57	0.6
    243	14.58	0.53
    2317	14.77	0.37
    2145	14.81	0.35
    2851	14.82	0.28
    5378	14.84	0.43
    2105	14.85	0.83
    1176	14.86	0.85
    281	14.88	0.41
    285	14.93	0.39
    1335	14.96	0.58
    2481	14.97	0.36
    5412	14.98	0.35
    1314	14.98	0.46
    1170	14.99	0.5
    205	15	0.5
    		
    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	14.29
    354	bq27411-G1C: 4.35V LiCoO2	17.38
    128	bq27421-G1A: 4.2V LiCoO2	32.03
    312	bq27421-G1B: 4.3V LiCoO2	35.49
    Best generic ID 3142		
    Warning: Deviation for best generic ID is above recommended level for this device / family. Consider using another device, flash based gauge or RAM programming of custom ID.		
    		
    		
    Device / Family #2		
    Generic Chem ID	Device/ Voltage/ Chemistry	max DOD error, %
    1210	bq27621:  (ALT_CHEM1) 4.3V LiCoO2	15.44
    1202	bq27621: (default) 4.2V LiCoO2	16.45
    354	bq27621:  (ALT_CHEM2) 4.35V LiCoO2	17.38
    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	14.29
    1202	bq27426: (ALT_CHEM1) 4.2V LiCoO2	16.45
    3230	bq27426: (default) 4.35V LiCoO2	18.36
    Best generic ID 3142		
    Warning: Deviation for best generic ID is above recommended level for this device / family. Consider using another device, flash based gauge or RAM programming of custom ID.		
    		
    		
    Warning: Discharge rate is too high. High rate reduces ID detection accuracy	 10 hr rate is recomeended. Total discharge time is less than 5 hrs	 t_hrs=  4.4701775
    
    , decide_chem_ID.log

    At the end of the following log contains the full discharge cycle, which I accidentally overdischarged the battery, which also power the gauge on the board, so the log stop here.

    learning_log_3.log

    According to your "If your taper rate is high it may lead to the battery relaxing to a lower voltage which would prevent you from getting a valid OCV for first Qmax update", I think I will start from the GPC tool, try to use a external charger to properly charge the battery, also use a external cement resistor as the load to discharge to 3.0 V.

    Thanks again for the help, and I will update after I re-do the record.

    Benjamin

  • Hello Benjamin,

    Yes I would recommend cycling the battery according to the battery manufacturer specification for the GPCCHEM process. Then you can change the voltage range for your application. This should help you complete the learning cycle.

    Using a bad matched chem ID can prevent successful learning, since we base the OCV to DOD readings on the chem ID programmed.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    I had re-try the GPCCHEM process. This time, I charged the battery until the current is lower than 60 mA, and the voltage after relax is 4161 mV instead of 4095 mV. 

    I got a chemistry ID of 2375 from GPCCHEM, and this is a Lithium polymer battery, the same as our battery. But the capacity of this 2375 battery is 1800 mAh, while our battery is a 6000 mAh one. Will this affect the accuracy of the gauge? Even if I change the Design Capacity in Data Memory to 6000 mAh.

    (The report also warn me that the Deviation (5.39%) is above recommended level.)

    Thank you for your help.

    Sincerely,

    Benjamin Kao

  • Hello Benjamin,

    That chem ID is most likely a much better match since it is the same chemistry. The capacity has no meaning in regards to the chem ID, it is based on an OCV vs DOD table, not capacity. The Design Capacity and Qmax are used in connection with the DOD points.

    Sincerely,

    Wyatt Keller

  • Hello Wyatt,

    Thanks for your kind help.

    After changing the Chem ID, we performed a successful learning cycle.

    Sincerely,

    Benjamin Kao