Seatalk as a power supply ?

[jim5099]

The power supply for the tiny bulb in my binnacle Plastimo compass has failed because the wiring has rotted. Running a replacement power supply will involve dismantling the Whitlock pedestal and is not my first choice. The nearest alternative power supply is the 12v on the Seatalk bus for the instrument cluster. Can anyone advise if it is advisable or not to tap into the Seatalk 12v positive ? I understand that the bulbs will always be on when the instruments are powered on.
Thanks for any guidance.

 

[prv]

I can't see why not, but await the input of those who know more about Seatalk than I do

Important to note that power cables near compasses should always be twisted to neutralise their magnetic fields.

Pete

 

[nigelmercier]

It wouldn't be ideal, can't you pull a new wire through?

 

[nimbusgb]

Go for it.

If you are worried about current draw replace the compass approx 50 ma 'wheat grain' lamps with led's at around 20ma but the saving is nominal.

 

[Ric]

It will be ok.

For many years the ST4000 wheel autopilot on my boat was running entirely from the Seatalk power! The installer had not connected the dedicated power leads to the ST4000 control head, so it was drawing all its power from the Seatalk network.

 

[jwilson]

It will be ok.

For many years the ST4000 wheel autopilot on my boat was running entirely from the Seatalk power! The installer had not connected the dedicated power leads to the ST4000 control head, so it was drawing all its power from the Seatalk network.

Mine was installed the same way on a new boat, drawing power from Seatalk. The autopilot intermittently but very occasionally went berserk, slamming into violent turns. The engineer who investigated it said it should not be fed 12 volts via Seatalk. Curiously though the tiny compass light had it's own 12 volt supply, so that now also powers the autopilot, which seems to have cured the problem.

The compass bulbs are usually very low power - unlikely on their own to cause a problem if powered by Seatalk, but if your instruments include an autopilot also fed power by Seatalk (which it should not be) the tiny extra current might just trigger problems.

 

[AngusMcDoon]

You could connect it to the yellow data line. Then you'd be able to see the Seatalk messages go past as the light flickers away.

 

[jim5099]

Many thanks to all contributors. The existing "wheat grain" bulbs work ok and I have spares so I'll stick with those. No, the supply cable will not pull through the pedestal so I cannot easily run a new cable.

I'll tap it off the Seatalk +ve and let you know the outcome.

Jim (Dufour36)

UPDATE: works fine !