Originally Posted by Privilege
I must confess to having been slightly confused when I set the system up in that the chart plotter has a power supply and the auto pilot has a power supply therefore when they’re both turned on the network has two separate power supplies which goes against the guidance. Surely the seatalk network can’t carry enough current
to supply the auto pilot? Is it right therefore that I should always have the auto pilot turned on but if I don’t want to use it, I disable it via the plotter?
There are two types of devices in a SeatalkNG/ N2k network regarding power.
Devices that draw little current are powered by the red 12V & black 0V wire of the network. Examples are the log, depth
instruments. This is convenient, just hook such device to the network and it is connected to both power and data.
Devices that are more power hungry can’t be fed through the thin network wires and need a dedicated power supply. Examples are your plotter / MFD, radar
Now comes the tricky bit. To power the 12V wire of the network, there are two possibilities. The first is a dedicated power drop cable. In the SeatalkNG network this is a red drop cable. This connects the blue backbone to your battery. The second possibility is that one of the ‘power hungry’ devices has an internal connection between its dedicated power supply and the 12V power wire in the drop cable which connects it to the backbone. Through this internal connection the power supply not only powers the device (e.g. autopilot) but also powers the backbone. In itself convenient combination of functions, you don’t need a separate power drop cable anymore, however it is a power supply in hiding!
Troubles may arise when using both a ‘power feeding’ device AND a separate power drop cable. Due to differences in wire resistance these two power sources, even originating from the same battery, may inflict unwanted currents in the network. How and why is beyond my knowledge, but Raymarine and other manufactures strongly oppose two power feeding points in one network.
Luckily the remedy is relatively simple. You can either simply remove one of the two power supplies, and since you can’t disconnect the dedicated power supply of your MFD or autopilot in most cases the power drop cable has to go. The other solution is to disable the internal power connection within a ‘feeding’ device. This may be achieved by a software
setting, a jumper setting or similar. But if this is not possible there is always a bomb-proof solution: cut or disconnect the red & black 12V wires of the drop cable of the 'feeding' device. The data connection will remain intact.
I hope this helps.