Compensating for cell 1 current during .aux file generation

Hi Wade,

Before the start of the .aux generation, all cells must be balanced as close as possible. The aux file generation tools and Qmax / Ra computations take into account the slight variations in cell voltages that are expected.

So the slight differences in cell voltages will not cauase detrimental effects on the calculations and parameter extractions.

Regards,

Ben

Hi Ben

We have consistently noticed cell 1 having 5% less Qmax compared with the other cells, is this more than you would expect?

We have always started with a well balanced pack and followed the .aux file generation procedure as outlined in your documentation.

Below is a typical .aux file that we generate using the 'actual' method, showing the differences in both Qmax and the Ra values. Incidentally, what do the Ra[0] - Ra[14] numbers represent?

# bq78PL114 auxillary chemistry data for chemistry type  146
# aux_gui version 2.00 - Actual
# based on H:\Program Files\Texas Instruments\bqWizard 3\Data Logging Files\take1.csv log file
# Generated for 3S1P pack
# Generated : 15/12/2010 9:55:41 AM
bqWizard # Application
2.5 # minimum BqWizard  version
1 # # of files
15 # File #
AuxChem # File Type
2 # ChunkSize
150 # Total bytes
##############################################
# Comments to be included in the .aux file
##############################################
    1 # Aux_Chem serial
  109 # Tau10
 2930 # NDI_LowT
 3030 # NDI_HighT
   15 # NDI_SOC
    0 # Spare0
   32 # NDI_GAIN
    0 # Spare1
    0 # Spare2
    0 # Spare3
    0 # Spare4
    0 # Spare5
########### cell 1 ##################
    5 # NDI_Initial
    5 # NDI
 4740 # QMax
 2367 # QRem
    0 # Rzero
    0 # Spare
   19 # Ra[ 0]
   24 # Ra[ 1]
   40 # Ra[ 2]
   41 # Ra[ 3]
   25 # Ra[ 4]
   22 # Ra[ 5]
   36 # Ra[ 6]
   35 # Ra[ 7]
   24 # Ra[ 8]
   18 # Ra[ 9]
   12 # Ra[10]
    8 # Ra[11]
   10 # Ra[12]
   17 # Ra[13]
   30 # Ra[14]
########### cell 2 ##################
    5 # NDI_Initial
    5 # NDI
 4990 # QMax
 2495 # QRem
    0 # Rzero
    0 # Spare
   18 # Ra[ 0]
   23 # Ra[ 1]
   36 # Ra[ 2]
   41 # Ra[ 3]
   27 # Ra[ 4]
   22 # Ra[ 5]
   36 # Ra[ 6]
   34 # Ra[ 7]
   23 # Ra[ 8]
   18 # Ra[ 9]
   13 # Ra[10]
   11 # Ra[11]
   13 # Ra[12]
   22 # Ra[13]
   39 # Ra[14]
########### cell 3 ##################
    5 # NDI_Initial
    5 # NDI
 4960 # QMax
 2478 # QRem
    0 # Rzero
    0 # Spare
   18 # Ra[ 0]
   23 # Ra[ 1]
   39 # Ra[ 2]
   41 # Ra[ 3]
   27 # Ra[ 4]
   22 # Ra[ 5]
   37 # Ra[ 6]
   34 # Ra[ 7]
   23 # Ra[ 8]
   18 # Ra[ 9]
   11 # Ra[10]
   12 # Ra[11]
   14 # Ra[12]
   24 # Ra[13]
   42 # Ra[14]

Hi Nigel,

The "The Ra table consists of 15 values of cell impedance, stored in milli-Ohms, that are a function of cell SOC.
Each series cell can have a different Ra table depending on its measured performance." --more detail in page 77 of the TRM

These values are used in TI proprietary algorithms to compute the Gas Gauge parameters

Ben

Hi Ben

Thank you for pointing out that new section of the TRM, it clears up a few things, although I still have a couple of questions

When we generate our .aux file, we tend to get an impedance that varies between 10 and 20mR, and then increases dramatically near 0% SOC. This is the expected trend, although we expect much lower values of impedance, between 1 and 5mR at the higher SOCs, as we are using high-rate cells, capable of 45C continuous discharge. The 'NDI_Initial' and 'NDI' values generally come out as '2', which is close to what we would expect for the cell's impedance, if these are in units of m-ohm.

So, How is 'NDI_Initial' and 'NDI' calculated, and what are the values used for?

Why are the Ra values so much larger than the NDI values?

How is impedance (above 10% SOC) calculated during a .aux file run when there is no pulsed discharge or charge during the data collection (except for the first 10% SOC during charging)?