The main battery is permanently tied to the hot battery bus which feeds two consumers: the ELT and the pilot map reading light. This makes possible to use the light even before boarding the plane and ease boarding, but it also makes this light a perfect tool for draining the battery.

Both left hand (LH) and right hand (RH) main busses are connected to the battery bus via circuit breakers. Both main busses feed the respective engine ECU busses via two diodes, to prevent any back current. When the electric master switch is turned on, the hot battery bus is connected to the battery bus. On both sides, the main bus and engine bus are then fed by the battery. Each engine ECU bus is also fed by an ECU backup battery, to avoid temporary loss of voltage if the alternator or the main battery cannot sustain a momentary high load, but more on this later on.

The LH and RH alternators are connected to both their respective main bus (via the alternator relay) and engine ECU bus (directly). As both main busses are inter-connected via the battery bus the load between the alternators can be balanced. As all diesel engines, there is one engine master switch per engine. When it is activated, the ECUs are connected to the engine ECU bus and the alternator is connected to the excitation battery. The same excitation battery feeds both alternators. Each engine is started separately by actuating the starter switch, which is a key with three positions: “off – left – right”, thus making impossible to start both engines simultaneously.

The 7th bus is the avionics bus, which is fed from the RH main bus, via a relay controlled by the avionics switch. This asymmetrical connection might seem strange, but remember that both main busses are connected together via the battery bus, so even if the main battery and the right alternator are lost the avionics bus is still fed by the left alternator.

The voltage showing on the G1000 is measured at the battery bus.

The AMP showing on the G1000 is measured by the sensor at the generator.