[TG] SeatalkNG and Seatalk power issues.

[Pan76]

My SeatalkNG system is somehow powering the old autopilot ST7000/300 and ST50 instruments.
And the autopilot is powering the SeatalkNG backbone.
Is this normal? Can I have the backbone powered without instruments/ap getting powered?

System:
C140W connected to STNG converter, from that a backbone cable to a STNG terminal where a AIS650 is connected and the power to STNG is supplied here.
From this terminal a backbone cable to aft conn station with a C90W.
Backbone is terminated acc. to instructions.

The converter is connected to one of the two Seatalk connections on the course computer, other units(ie ST50 instruments)are also connected here.

The autopilot/instruments have a separate switch, switching it on the STNG backbone gets powered. With switch off the autopilot/instruments gets powered when powering the STNG.

[Tom - Raymarine - Moderator]

Hello Pan76,

The ST1-STNG convertor can pass power through in either direction. This is by design in order to simplify installations, but is causing the problem you're seeing. This shouldn't be happening, you should only have a single point of power for your combined network. Multiple points of power can cause a range of problems including:

• incorrect fusing/circuit protection
• electrical noise, as current oscillates between taking one path or another, especially if both supplies aren't straight from the same source
• damaged SeatalkNG/NMEA2000 chips in STNG devices
  

You need to choose one source of power or the other, and disconnect the red +12V wire on the other one.

Regards,
Tom