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BQ27426: Inaccurate State of Charge while charging

William Huang28
Prodigy 180 points
Part Number: BQ27426
Other Parts Discussed in Thread: GPCRA0

Hello,

After applying a golden image data to the gauge, I am happy with the results when I am doing a full charge/discharge cycle (see graphs below). My learning cycle when for the golden image was: full battery charge/discharge (3000 mV - 4200 mV), then system's operating range charge/discharge (3100mV - 4100mV). 

Note: the data was collected my actual board - not the evaluation kit. All readings from fuel gauage.

Discharge graphs:

Full Charge Graphs:


However, when I perform a partial discharge then charge back to full, I am getting horrendous accuracy SoC readings while charging. More concerning, however, is when the charging is complete, the gauge will report 100% and then after a while drop the reading down below 100%. See graphs below:

Partial Discharge then Charge back to full graphs:


(Note: I also performed the test to determine to correct ChemID, and am using ID 1202 after getting the results from the GPC tool)

  • 0
    Prodigy 180 points

    And here is my gg file for reference

    SystemCycle2.gg.txt 
    * Texas Instruments Data Flash File
* File created Thu Mar 22 08:51:19 2018
*
* Device Number 426
* Firmware Version 2.02
* Build Number not available
* Order Number not available
*
* bqz Device Number 426
* bqz Firmware Version 2.02
* bqz Build Number 1
*
* Field Order: Class name, Subclass name, Parameter name, Parameter Value, Display Units
"Configuration","Safety","Over Temp","55.0","°C"
"Configuration","Safety","Under Temp","0","°C"
"Configuration","Safety","Temp Hys","5.0","°C"
"Configuration","Charge Termination","TCA Set %","99","%"
"Configuration","Charge Termination","TCA Clear %","95","%"
"Configuration","Charge Termination","FC Set %","-1","%"
"Configuration","Charge Termination","FC Clear %","98","%"
"Configuration","Charge Termination","DODatEOC Delta T","5.0","°C"
"Configuration","Discharge","SOC1 Set Threshold","10","%"
"Configuration","Discharge","SOC1 Clear Threshold","15","%"
"Configuration","Discharge","SOCF Set Threshold","2","%"
"Configuration","Discharge","SOCF Clear Threshold","5","%"
"Configuration","Registers","OpConfig","25f8","Flag"
"Configuration","Registers","OpConfigB","0f","Flag"
"Configuration","Registers","OpConfigC","9f","Flag"
"Configuration","Registers","OpConfigD","23","Flag"
"Configuration","Power","Hibernate I","3","mA"
"Configuration","Power","Hibernate V","2200","mV"
"Gas Gauging","IT Cfg","OCV Wait Time","60","s"
"Gas Gauging","IT Cfg","Ra Filter","800","Num"
"Gas Gauging","IT Cfg","Res V Drop","32767","mV"
"Gas Gauging","IT Cfg","Samples to Wake","240","s"
"Gas Gauging","IT Cfg","Qmax Max Time","18000","s"
"Gas Gauging","IT Cfg","DOD Valid Time","25","s"
"Gas Gauging","IT Cfg","Fast Qmax Start DOD %","92","%"
"Gas Gauging","IT Cfg","Fast Qmax End DOD %","96","%"
"Gas Gauging","IT Cfg","Fast Qmax Start Volt Delta","125","mV"
"Gas Gauging","IT Cfg","Fast Qmax Current Threshold","4","Hr rate"
"Gas Gauging","IT Cfg","Fast Qmax Min Points","3","Num"
"Gas Gauging","IT Cfg","Max Qmax Change","20","%"
"Gas Gauging","IT Cfg","Qmax Max Delta %","10","%DCap"
"Gas Gauging","IT Cfg","Max % Default Qmax","120","%DCap"
"Gas Gauging","IT Cfg","Qmax Filter","96","Num"
"Gas Gauging","IT Cfg","ResRelax Time","500","s"
"Gas Gauging","IT Cfg","User Rate-mA","0","mA"
"Gas Gauging","IT Cfg","User Rate-mW","0","mW"
"Gas Gauging","IT Cfg","Max Sim Rate","1","Hr rate"
"Gas Gauging","IT Cfg","Min Sim Rate","20","Hr rate"
"Gas Gauging","IT Cfg","Ra Max Delta","8","4mOhm"
"Gas Gauging","IT Cfg","Min Delta Voltage","0","mV"
"Gas Gauging","IT Cfg","Max Delta Voltage","200","mV"
"Gas Gauging","IT Cfg","DeltaV Max dV","100","mV"
"Gas Gauging","IT Cfg","TermV Valid t","2","s"
"Gas Gauging","IT Cfg","Trace Resistance","0","mOhm"
"Gas Gauging","IT Cfg","Downstream Resistance","0","mOhm"
"Gas Gauging","IT Cfg","Predict Ambient Time","2000","s"
"Gas Gauging","IT Cfg","Design Energy Scale","1","Num"
"Gas Gauging","IT Cfg","Fast Scale Load Select","3","Num"
"Gas Gauging","IT Cfg","Chg DOD Correction Start SOC","90","Num"
"Gas Gauging","IT Cfg","Chg DOD Correction Taper Ratio","20","Num"
"Gas Gauging","Current Thresholds","Dsg Current Threshold","167",".1 Hr rate"
"Gas Gauging","Current Thresholds","Chg Current Threshold","100",".1 Hr rate"
"Gas Gauging","Current Thresholds","Quit Current","250",".1 Hr rate"
"Gas Gauging","Current Thresholds","Dsg Relax Time","60","s"
"Gas Gauging","Current Thresholds","Chg Relax Time","60","s"
"Gas Gauging","Current Thresholds","Quit Relax Time","1","s"
"Gas Gauging","Current Thresholds","Max IR Correct","400","mV"
"Gas Gauging","State","Qmax Cell 0","16015","Num"
"Gas Gauging","State","Update Status","00","Hex"
"Gas Gauging","State","Reserve Cap-mAh","0","mAh"
"Gas Gauging","State","Load Select/Mode","81","Hex"
"Gas Gauging","State","Design Capacity","2400","mAh"
"Gas Gauging","State","Design Energy","8890","mWh"
"Gas Gauging","State","Terminate Voltage","3100","mV"
"Gas Gauging","State","T Rise","20","Num"
"Gas Gauging","State","T Time Constant","1000","s"
"Gas Gauging","State","SOCI Delta","1","%"
"Gas Gauging","State","Taper Rate","218",".1 Hr rate"
"Gas Gauging","State","Sleep Current","10","mA"
"Gas Gauging","State","Avg I Last Run","-121",".1 Hr rate"
"Gas Gauging","State","Avg P Last Run","-119",".1 Hr rate"
"Gas Gauging","State","Delta Voltage","1","mV"
"Ra Tables","Ra0 RAM","Ra 0","50","Num"
"Ra Tables","Ra0 RAM","Ra 1","30","Num"
"Ra Tables","Ra0 RAM","Ra 2","34","Num"
"Ra Tables","Ra0 RAM","Ra 3","46","Num"
"Ra Tables","Ra0 RAM","Ra 4","38","Num"
"Ra Tables","Ra0 RAM","Ra 5","32","Num"
"Ra Tables","Ra0 RAM","Ra 6","37","Num"
"Ra Tables","Ra0 RAM","Ra 7","31","Num"
"Ra Tables","Ra0 RAM","Ra 8","32","Num"
"Ra Tables","Ra0 RAM","Ra 9","35","Num"
"Ra Tables","Ra0 RAM","Ra 10","39","Num"
"Ra Tables","Ra0 RAM","Ra 11","39","Num"
"Ra Tables","Ra0 RAM","Ra 12","61","Num"
"Ra Tables","Ra0 RAM","Ra 13","115","Num"
"Ra Tables","Ra0 RAM","Ra 14","200","Num"
"Chemistry Info","Chem Data","Q Invalid MaxV","3809","mV"
"Chemistry Info","Chem Data","Q Invalid MinV","3744","mV"
"Chemistry Info","Chem Data","V at Chg Term","4100","mV"
"Chemistry Info","Chem Data","Taper Voltage","4000","mV"
"Calibration","Data","Board Offset","0","Counts"
"Calibration","Data","Int Temp Offset","0","°C"
"Calibration","Data","Ext Temp Offset","0","°C"
"Calibration","Data","Pack V Offset","0","mV"
"Calibration","Data","Ext a Coef 1","-11130","Num"
"Calibration","Data","Ext a Coef 2","19142","Num"
"Calibration","Data","Ext a Coef 3","-19262","Num"
"Calibration","Data","Ext a Coef 4","28203","Num"
"Calibration","Data","Ext a Coef 5","892","Num"
"Calibration","Data","Ext b Coef 1","328","Num"
"Calibration","Data","Ext b Coef 2","-605","Num"
"Calibration","Data","Ext b Coef 3","-2443","Num"
"Calibration","Data","Ext b Coef 4","4696","Num"
"Calibration","CC Cal","CC Offset","1","Counts"
"Calibration","CC Cal","CC Cal Temp","303.0","°K"
"Calibration","CC Cal","CC Gain","0.2380","Num"
"Calibration","CC Cal","CC Delta","283945.0625","Num"
"Calibration","Current","Deadband","5","mA"
"Security","Codes","Sealed to Unsealed","80008000","Hex"

  • 0 in reply to William Huang28
    TI__Guru* 76230 points
    Hello William,

    You will need to perform a gpcRa0 tweak of your cells. The issue is with the first set of resistance grid points, particularly ra0. Using our online tool gpcra0 will allow you make adjustments that will help improve the accuracy of the gauge. Pls follow the instruction in the user manual.

    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Prodigy 180 points
    Thanks for the reply Onyx.

    Does the test require the battery to be charged completely to battery's maximum voltage (4200mV)? Currently, the board has a charging IC that places the maximum voltage to 4100 mV.
  • 0 in reply to William Huang28
    TI__Guru* 76230 points
    I would recommend charging to 4.1V
    thanks
    Onyx