A simple venus-os service to log battery cell voltages in a CSV (-like) format.

Cell voltages are read from "com.victronenergy.battery" service (the first one found).

The number of cells logged is 16 (hardcoded value).

Log-interval is 60 seconds, every minute a entry is written to the log file (hardcoded value).

The log file is stored in "/data/db/cell-logger.dat" (hardcoded value). Use "scp" to copy this file to your workstation for evaluation.

The file format is simple, the fields are separated by a blank. Voltages are in [volt] and current is in [ampere], positive current means battery is charging, negative current means discharging.

<unix-timestamp> <battery-voltage> <battery-current> <cell-voltage1> ... <cell-voltage16>

For example:

...
1664070073 52.700000 -5.790000 3.305000 3.307000 3.305000 3.304000 3.304000 3.305000 3.305000 3.307000 3.286000 3.286000 3.282000 3.285000 3.288000 3.291000 3.290000 3.285000 
1664070133 52.700000 -4.910000 3.305000 3.307000 3.305000 3.304000 3.305000 3.305000 3.305000 3.306000 3.286000 3.286000 3.283000 3.285000 3.288000 3.290000 3.290000 3.285000 
1664070193 52.700000 -4.800000 3.305000 3.307000 3.305000 3.304000 3.305000 3.305000 3.305000 3.306000 3.287000 3.286000 3.283000 3.285000 3.289000 3.291000 3.291000 3.285000 
...

See plot.sh and plot-cell-data.gnuplot for a example how to copy the logfile from your venus-os box and to plot the data using gnuplot.

The file "cell-logger.dat.example" contains some example data.

To plot it using gnuplot, use something like this:

cp cell-logger.dat.example cell-logger.dat
gnuplot -e "tzoffset=7200" plot-cell-data.gnuplo

Example plots:

• Create a config-section at the beginning of "dbus-cell-logger.py" to allow modification of some constants (log-interval, log file path...).