Another thing that I would have tackled differently á posteriori is the implementation of all the logics that connect the different state and alarm signals and control inputs. While at the beginning of the project, their number and also their interdependence seemed easily manageable, the complexity increased over time.

So, my approach of using e.g. some combiner diodes to form a logical “OR”, to feed signals to both ends of a relay coil for an “A AND NOT B” or to use old-fashioned timer circuits eventually ended up in quite a messy harness of wires and circuit boards.

I did use a few microcontrollers (heater control, control of the cooling system, DC/DC converter control), but not a central processor - which would for sure have made the setup much tidier and easier to manage.

Following table shows the numerous alarms that have to be handled somehow, and their connection to control lines or logics circuits. Each row covers one alarm. “Trigger condition” means the condition upon which the alarm is raised. In column “goes to” we see to which destination the alarm is connected. For example, the “HV idle voltage too low” alarm (first row) connects to the “HV alarm unit” on the “BMS peripherals” circuit board. This circuit will raise the “combined HV alarm”, with “HV idle voltage too low” as one possible trigger (see column B).

As another example, the “HV isolation check failed” alarm generated by the HV isolation check board actually provides one “ground contact” and one “active 12V” output. The ground contact output goes to the immobilizer latch (which avoids that the immobilizer is triggered during driving), while the “active 12V” output again is fed to the HV alarm unit of the BMS peripherals board.

link to alarms table (jpg), right-click and save as file (or directly open with a picture viewer)

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