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Old 17-12-2016, 11:14   #1
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Wiring compass light to two separate circuits

Hi all,

I'm re-wiring the light on my binnacle mounted compass (Danforth Constellation 5"). I'd like the light to be on whenever either my lower running lights OR mast-mounted tri-color are on. The running lights and tri-color are in separate circuits and I wouldn't expect to have them both "on" at the same time.

Obviously the ground will go to the main ground bus bar for the DC circuits, but can I then have two positive leads with one going to the tri-color breaker and one to the running lights breaker? I suppose I should use diodes in the hot leads to prevent unintentionally connecting the two circuits?
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Old 17-12-2016, 11:23   #2
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Re: Wiring compass light to two separate circuits

You can wire it to both, but if they're on separate breakers I would add a separate in-line fuse on the compass light hotwire that's sized for the compass light/wire. Otherwise the amp rating on the compass light could be the total (added) rating of both breakers combined.
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Old 17-12-2016, 13:48   #3
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Re: Wiring compass light to two separate circuits

You need the diodes, otherwise both the deck-level lights and the mast-top light will turn on together every time.

An alternative would be to wire both sets of lights onto a single breaker, and add a selector switch to select which lights are on - then wire in the compass light after the breaker, but before the selector switch.

Or just use another breaker for the compass light - but you might be asking the question because you're trying to free up this breaker for something else.
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Old 17-12-2016, 14:17   #4
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Re: Wiring compass light to two separate circuits

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Diodes are the answer.....however I've noted since changing the deck level lights to led that the green nav light faintly illuminates when the tricolor is on. The diodes are not blocking absolutely.
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Old 17-12-2016, 14:51   #5
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Re: Wiring compass light to two separate circuits

Of course, diodes. I stand corrected.
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Old 17-12-2016, 16:10   #6
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Re: Wiring compass light to two separate circuits

Why have your compass light wired into your running lights at all? Ours is independently wired with a simple switch on our instrument panel and we frequently have it illuminated regardless of running lights, often, if not always when we're anchored out so that, on a shoot dark night, we know what direction the yacht is pointed in the event we have to make an unexpected break for deeper water.

FWIW...
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Old 17-12-2016, 17:12   #7
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Re: Wiring compass light to two separate circuits

simple and can free up a breaker for something more useful. My homemade deal. piece of plexiglass, tapped, brass sheetmetal, 3 amp diodes from RadioShack.

I also have my breaker panel lights wired in so they will illuminate when either set of lights is on

If other lights are glowing, diodes are bad or there is stray current
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Old 18-12-2016, 08:10   #8
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Re: Wiring compass light to two separate circuits

Why not just put the compass lighting on its own, dimmable circuit and keep it separate from the mast, and deck nav lights?
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Old 18-12-2016, 09:22   #9
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Re: Wiring compass light to two separate circuits

Quote:
Originally Posted by jls095 View Post
Hi all,

I'm re-wiring the light on my binnacle mounted compass (Danforth Constellation 5"). I'd like the light to be on whenever either my lower running lights OR mast-mounted tri-color are on. The running lights and tri-color are in separate circuits and I wouldn't expect to have them both "on" at the same time.

Obviously the ground will go to the main ground bus bar for the DC circuits, but can I then have two positive leads with one going to the tri-color breaker and one to the running lights breaker? I suppose I should use diodes in the hot leads to prevent unintentionally connecting the two circuits?
Put a blocking diode in the supply wires.
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Old 18-12-2016, 09:29   #10
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Re: Wiring compass light to two separate circuits

I've done it with diodes: It works well and quite simple to make.
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Old 18-12-2016, 09:32   #11
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Re: Wiring compass light to two separate circuits

Solutions:

1. Control your running and trilight with one breaker (you could fuse each circuit separately so if one circuit shorts it doesn't take out the other) and use the other breaker for the compass light.

2. Control your running light and trilight with separate double throw switches, the second throw on each to the compass light.

3. Diodes from running light and trilight switches to the compass light, blocking current flow to the alternate circuit light.

4. Use (or add) a spare breaker to the panel to have separate for each.

5. Use one breaker from main panel to feed a new subpanel with separate breakers for each (freeing up a breaker on the main panel).
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Old 18-12-2016, 11:27   #12
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Re: Wiring compass light to two separate circuits

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Originally Posted by Sailmonkey View Post
Attachment 138123

Diodes are the answer.....however I've noted since changing the deck level lights to led that the green nav light faintly illuminates when the tricolor is on. The diodes are not blocking absolutely.
You may want to check the value of your diodes? They may be to large thus allowing some bleed for the LEDs. Just a thought.
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Old 18-12-2016, 13:16   #13
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Re: Wiring compass light to two separate circuits

You could use a pair of double-pole double-throw relays, rigged so that each one, when energized, broke the "compass power" from the other source as it connected compass power for it's own source. Effectively making them into a pair of two-way light switches. Depending on how the bulbs are set up, physically, it may also be possible to just add a second set of bulbs alongside, and power one set from each circuit, so it is one-or-the-other whichever you choose, and nothing shared common to the two lighting circuits.
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Old 18-12-2016, 13:58   #14
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Re: Wiring compass light to two separate circuits

Why are some making a simple two diode fix a major electrical rewiring? If the LED has a little bleed going to it, find better diodes or don't worry about it.
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Old 18-12-2016, 16:03   #15
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Re: Wiring compass light to two separate circuits

Diodes shouldn't be needed. As your trilight and lower running lights are on separate switches it is easy. The output of both switches goes to their respective loads as well as the positive of the compass light. As long as the lower running lights are off the current cannot run through the switch to them when the compass light and trilight are on - and vice versa.
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