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12V diode combiner circuit question

  1. May 25, 2017 #1
    Hello, I'm currently doing an electrical refit on a 29' Bristol. I have an anchor/steaming light for the top of the mast. I'm connecting them to two separate single pole single throw breakers. My problem is that I need the steaming light (fwd light) to be able to come on indipendantly from the anchor light (both light) and vice versa. I know I can just put a diode in-between the breakers to solve this problem. But I'm not sure what sort of diode I need. It's a 12v system, each breaker is 5 amps. The lights themselves don't even draw one amp combined. Any help would be greatly appreciated. Thanks!
  2. jcsd
  3. May 25, 2017 #2


    Staff: Mentor


    I don't understand your question. Each light has a ground connection. Each light has its own single pole switch for the positive side. You can turn them on/off independently. Why the question?

    Edit: many modern mashead anchor/steaming/navigation/emergency flash LED lights come with a bit of smarts. They use one positive wire and one negative ground wire for all the lights. The control switch you push once for anchor, twice for steaming, three for nav, four for flash, five times for off. That is simpler than running separate wires for each. By the way, it is illegal to use your anchor light and steaming light at the same time.
  4. May 26, 2017 #3
    Sorry, let me explain a little better. When I flip the breaker for the anchor light, I need both lights to turn on, when I flip it for the steaming light I just need the forward light to turn on.
    The light it self is a single component with two bulbs. There are two positives coming out and they share a negative.

    So this is a work project, I'm not going to lie I'm not much of a boater myself, I just work on them. So when it comes to coast guard regulations I'm pretty clueless. We do have other techs that sail and when talking with them they all said with that light that is the correct set up. I know it should be on a rocker switch but we have limitations in what we could add. So making it work on our main DC
    panel breakers was our best option.
  5. May 26, 2017 #4


    Staff: Mentor

    What is the matter with that? Why doesn't that do what you need?
  6. May 26, 2017 #5
    It works if you throw both breakers for the anchor, and just the one for the steaming. But I want to be able to throw the anchor light breaker and activate both lights, while keeping the steaming on its own separate breaker as well.

    I know I can achieve this with a diode, my main question was if there was a certain diode I needed for Marine applications. Or would any old 12v 3 amp diode do the trick.

    I apologise for any confusion. I really do appreciate the help.
  7. May 26, 2017 #6


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    Gold Member
    2017 Award

    any normal diode ... there are no such things as marine diodes that I'm aware of
    Last edited: May 27, 2017
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