• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 356 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ78350-R1: Design Capacity not reached - temperature range too high?

Philipp Knabl
Prodigy 70 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, GPCCEDV

Hi everyone,

we have a bq78350r1 on a 7S4P pack. We successfully created a CEDV GI in a temperature range of -20°C-+40°C. So lowtemp = -20°C; roomtemp = 0°C; hightemp = 40°C, because this is the temperature range the battery pack will be in use.

We got good results from the GPC Packager tool and all the deviations were within recomended range. However, when we did one charge/discharge cycle we could see the battery pack could only learn around 11.900mAh and not the designed 12.800mAh. 

So my question is is the temperature range of the CEDV log files too high? Our approach would be to skip the -20°C and start two more measurements with roomtemp = 20°C and set lowtemp = 0°C and say that the design capacity is reachable in "normal" temperature range but whenever it gets colder there could be some losses in capacity.

Any help is appreciated!

GI_v06.gg.csv3343.lowtemp_highrate.csv3343.lowtemp_lowrate.csv7167.roomtemp_lowrate.csv7167.hightemp_lowrate.csv1781.hightemp_highrate.csv1781.roomtemp_highrate.csv 1781.GPCPackaged.zip

  • 0
    TI__Guru** 105640 points

    Hello Philipp,

    The BQ78350 with CEDV heavily relies on coulomb counting in order to provide SOC/RemCap estimations. If during your testing you are switching loads and temperatures in large steps it will impact the accuracy of the gauge. CEDV will do some temperature and load rate compensation but it performs best when at fairly consistent conditions (load and temperature) for example 10degC to 40degC with load varying from 0.5C to 1C.

    Did you also send the GPCCEDV result? I didn't see it in the files shared.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hi Wyatt thanks for your reply!

    That is what we are thinking as well. We just thought that it maybe works as well but the capacity deviations are just too big.
    I think I shared the GPCCEDV result as well (the whole .zip) but I can share it again with you.

    Fullscreen 8004.GPC_CEDV.txt Download 
    GPC CEDV tool, rev=60		
Configuration used in present fit		
ProcessingType=1		
NumCellSeries=7		
CellTermV=2500		
LearnSOC%=7		
FitMaxSOC%=9		
FitMinSOC%=3		
ChemType=1		
ElapsedTimeColumn=0		
VoltageColumn=1		
TemperatureColumn=2		
CurrentColumn=3		
		
CEDV parameters resulting from the fit. If EDVV bit is set to 1, EMF and EDVR0 have to be multiplied by the number of serial cells when written to data flash		
		
EMF	3470	
EDVC0	311	
EDVC1	0	
EDVR1	1190	
EDVR0	2251	
EDVT0	4030	
EDVTC	6	
VOC75	27547	
VOC50	26659	
VOC25	26265	
		
		
Recommended SOC deviation tolerance at EDV2 point is  < 5% for low temperature and <3% for room and high temperature		
		
Deviations for this set of parameters are given below for each file		
		
file	SOC error, %	pass
roomtemp_lowrate.csv	-0.261106611944629	1
roomtemp_highrate.csv	0.129455408185277	1
hightemp_lowrate.csv	-0.455996613046685	1
hightemp_highrate.csv	-0.294817525121223	1
lowtemp_lowrate.csv	1.64086970119226	1
lowtemp_highrate.csv	-0.988560262544351	1
		
Deviations are within recomended range. CEDV parameters are suitable for programming the gauge

    Best,

    Philipp

  • 0 in reply to Philipp Knabl
    TI__Guru** 105640 points

    Hello Philipp,

    Yes I think if you were more consistently at a temperature or load you would see the accuracy reported by GPCCEDV tool, but with large changes it will cause larger SOC error between cycles.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    We did another cycle at room temperature (25°C) and created another CEDV result. This time even better results. 

    However it seem that we still do not reach the desired capacity. We are currently running some tests and I will share the log files with you asap.
    Attached you find the updated CEDV parameters.

    Fullscreen 3554.GPC_CEDV.txt Download 
    GPC CEDV tool, rev=60		
Configuration used in present fit		
ProcessingType=1		
NumCellSeries=7		
CellTermV=2500		
LearnSOC%=7		
FitMaxSOC%=9		
FitMinSOC%=3		
ChemType=1		
ElapsedTimeColumn=0		
VoltageColumn=1		
TemperatureColumn=2		
CurrentColumn=3		
		
CEDV parameters resulting from the fit. If EDVV bit is set to 1, EMF and EDVR0 have to be multiplied by the number of serial cells when written to data flash		
		
EMF	3590	
EDVC0	503	
EDVC1	0	
EDVR1	684	
EDVR0	3522	
EDVT0	4735	
EDVTC	4	
VOC75	27547	
VOC50	26659	
VOC25	26265	
		
		
Recommended SOC deviation tolerance at EDV2 point is  < 5% for low temperature and <3% for room and high temperature		
		
Deviations for this set of parameters are given below for each file		
		
file	SOC error, %	pass
roomtemp_lowrate.csv	0.564484537100435	1
roomtemp_highrate.csv	-0.356482760850092	1
hightemp_lowrate.csv	-0.638899924824001	1
hightemp_highrate.csv	0.882676624232614	1
lowtemp_lowrate.csv	-0.129361107804413	1
lowtemp_highrate.csv	0.342087000239217	1
		
Deviations are within recomended range. CEDV parameters are suitable for programming the gauge

    Best,
    Philipp

  • 0 in reply to Philipp Knabl
    TI__Guru** 105640 points

    Hello Philipp,

    Can you clarify the capacity you're expecting? CEDV FCC is based on the coulomb count, so it will fluctuate as load and temperature changes, I would not expect you to always meet design capacity.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 70 points

    Hello Wyatt,

    The capacity we are expecting is around 12.500mAh but we are reaching only about 11.700-11.900mAh

    Best,
    Philipp

  • +1 in reply to Wyatt Keller
    Prodigy 70 points

    Hi Wyatt,

    we also did some cycles with the new CEDV parameters (0°C-40°C) and we also only get around 11.9Ah. So I guess thats the capacity the battery pack can deliver. It is just a little confusing because the cell data sheet says 3.2Ah per cell.

    Anyhow, I will close this issue. Thanks for your help.

    Best,
    Philipp