Still working on the battery management system. Had some major trouble with that 4D software. It is buggy and inconvenient … simply not ready really for serious work, at least to my standards. Nevertheless I spent several hours testing and finding workarounds for various issues.
It was also an opportunity to start from scratch, almost, and this time I made a structure before I started putting the screens together and removed a bit of clutter.
There might be still a change here and there as I complete the software, but this is pretty much what I can see happening.
The top image shows the entry page for the BMS with the power switch. The Teutanic has now its own flag. Just couldn’t resist that inner voice I had to visualise the idea. Just a play with symbols.
After power on the unit shows the menu.
From there one can select various display pages. When a page is selected it will stay visible for 3 minutes before the screen goes black. A simple touch will wake the screen up again. The unit will run and collect data, and execute the check routines even while the screen is dark.
The main page with the meter for battery voltage and load current. if an exception occurs the led will blink and one can press the STATUS button and get to the STATUS page.
The status page shows some information and also allows to rest the charge and load connections if an exception condition has separated either charge, load or both. More information about the condition can be found on the LOG page.
Each individual cell is monitored by the BMS and if there is an imbalance between the cells while charging and a certain threshold of charge is reached, the BMS will separate the charge line and start balancing the cells.
The active balancing can be disabled in case a manual balancing is preferred.
The charge process can be observed using the CHARGE page.
The power measurements based on voltage and current requires sensors to acquire the data for calculation. The BMS has a real time clock as a time base for calculating kWh and the current sensor is a hall effect sensor. I am not using shunts. I find them inconvenient to install. They waste space and require additional connections, which create additional connection resistance. The hall effect sensors are contact less and easy to install at any place.
I found a source of reasonably priced hall effect sensors for up to 500A. Have not yet decided on the range for all the sensors yet.
Since this is not a commercial unit I don’t have to design it to use the cheapest components. Surely shunts are cheaper than hall effect sensors.
Parameters for the exception recognition are entered via the settings page.
I can monitor CAN bus messages and check the communication with the Ethernet gateway of the central system.
I also can simulate certain situations to test the system and connected components without forcing the battery cells into any of the test conditions.
These functions will remain in the system for diagnostic purposes if something is not working the way it should.
This pages are now implemented in the display and most of the monitoring routines are done. I do not have the current sensors yet but when they arrive I can start testing the BMS connected to the actual battery and load.
This is still a few weeks away. The sensors come from the US and I will surely have no time for a detailed test until I am back from QLD with the shell.