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Circuit design help, dual inputs

  1. Feb 29, 2012 #1
    Hey! New to the forums here, and I wonder if you guys could give me some help.

    I've got a problem! :D

    Problem: Let me give you the scenario. I've got some GPS equipment that runs on ignition, constant, and ground.

    I have a barge that has two motors, and two ignition switches.

    I need to power the ignition wire on the GPS equipment with a constant 12v 3amp source coming off either/both of the motor ignition switches, without backfeeding into the other ignition.

    MY Solution: What I have so far, is both ignition circuits being branched off into 3 volt fuses, and different diodes. Before each diode is an LED that shows me if I'm getting power or not on that circuit, with both - legs going to a common ground. AFTER the diodes it branches out to the ignition wire on the GPS device harness.

    Problem: [1] I need to make sure I don't backfeed voltage into either ignition circuit if there is a component failure [2] I need to make sure all components are fused [3] I need to make sure the ignition circuit on the GPS equipment harness doesn't receive more than 12v @ 3A, and I need to maintain a constant 12V while either or both ignitions are on to my GPS device.

    Question(s): [1] Should I use a capacitor in line with the ignition harness circuit on the GPS device to help stabilize my voltage? [2] Would I be better off preventing backfeed with relays instead of diodes?

    Would really appreciate the help, I'm new to this kind of thing!

    edit: circuitlab diagrams would be VERY helpful for showing examples! Thanks!
  2. jcsd
  3. Mar 1, 2012 #2

    Help please! :(
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