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Old 24-02-2016, 11:58   #16
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Re: How to get power to compass? Wires seem VERY small.

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Originally Posted by MarkSF View Post
"via switch (perhaps nav lights; you have these for night sailing when you need a compass light, correct?) and fuse or breaker from the house bank."

I think I would like to have separate breakers / switches for nav lights and instrument lights, for the simple reason that I don't want a fault in my instrument lights preventing use of the nav lights.
Most modern instruments have LED backlighting, powered and switched, by the instrument itself.

Wired properly, there should not be an electrical circuit failure for the life of the vessel. In the event of a fault, proper current limiting would open the compass circuit, should a short circuit occur which could otherwise affect the running light circuit.

I connect compass lights to nav running lights all the time.

If one wishes them separate (e.g. to reduce vessel visibility nightsailing in pirate waters), it could certainly be on a different switch, but this is not usually a consideration. Normally, if one needs the running lights on, the compass light should be on, and if one doesn't need a compass light, they don't need running lights.

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Old 24-02-2016, 12:10   #17
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Re: How to get power to compass? Wires seem VERY small.

A 3mm red led runs on about 1.5 volts at 15 ma. Instead of using a higher voltage battery and wasting power in resistors to bring the the voltage back down, simply wire the led to a D cell alkaline battery. I should be good for 1000 hours between battery changes. Do twist the wires near the compass, and check the compass reading with and without the light on to make sure that it doesn't change.
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Old 24-02-2016, 15:02   #18
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Re: How to get power to compass? Wires seem VERY small.

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Originally Posted by donradcliffe View Post
A 3mm red led runs on about 1.5 volts at 15 ma. Instead of using a higher voltage battery and wasting power in resistors to bring the the voltage back down, simply wire the led to a D cell alkaline battery. I should be good for 1000 hours between battery changes. Do twist the wires near the compass, and check the compass reading with and without the light on to make sure that it doesn't change.
All true, Don, but the deviation caused by 15 mA will be vanishingly small when compared to the errors found in a compass squashed into the footwell of a steel vessel, sans corrections. But your suggestions for the light source will work, and will cost virtually nothing. And the compass will be so inaccurate that there is little point in lighting it IMO!!

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