Originally Posted by sailabroad
My seatalk network is powered from my autopilot
and I just swapped out my old c120 with an e120 Classic
that i got on ebay.
It's not seeing any seatalk data
I noticed the seatalk red(+12 power) cable was connected on the seatalk plug
which goes into the e120 chartplotter
and remembered something about the network should only be powered from one end?, I think!?, but goggling everywhere even on the raymarine forums
hasn't turned up anything.
Anyone know anything about this?
You are correct that you should only power seatalk from one point (and any other bus for that matter)
With 2 power connections to seatalk you will end up with minor voltage level differences at each connection (which by its'self is not too bad), the introduction
sources on the power bus and "bad things" (TM) in the case of losing one of the power sources. See below.
The primary reason to power seatalk from one source only is should you power it from 2 sources then the current
supplied to the bus is shared from the 2 sources. Should you lose one of the sources then all the current
needed on the bus will be sourced from the single
active source. This could result in an over load of the conductors on the active supply or in the device supplying current to the bus.
As an example - Let's say that you power your seatalk bus from your AP and that it has a 10 A fuse for seatalk power. All of the wires, fuse, circuit board traces are sized to supply the 10 amps max on the bus.
As you grow the system you end up installing another device that also can supply power to the seatalk bus. But this device only has wiring
, fuse etc for 5 amps.
Best case when you lose the AP for whatever reason it is no longer able to supply the 10 amps. If you seatalk loads draw less than the 5 amps now available you have "no problem". But if the seatalk loads draw 10 amps it will blow the 5 amp fuse is short order and you have no seatalk instruments. Or... If your seatalk load is not too much over 5 amps it will take minutes to blow the 5 amp fuse and in the mean time you could be burning up traces in the instruments or in the power supply wires possible causing a fire.
Other variations exist.
is still a significant reason not to be minimized.