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  • Alternator wire routing question

    There is a hefty 6-gauge cable coming off the B+ connection on the backside of the alternator on Cardinal, which runs to the battery via the downstream side of the 80-amp Blue Sea circuit breaker, then via the battery selector switch, and on to the two batteries (a regular maintenance-free starter battery and a deep-cycle house battery).

    It seems odd to me that the alternator power would be run through that circuit breaker from the downstream side. Wouldn’t it have been more appropriate to connect that to the UPstream side of that breaker?
    -- Tim Taylor

    1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
    1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
    1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


    I wrote a song about a tortilla. Well actually, it’s more of a wrap.

  • #2
    Never heard the electrical terms ¨downstream side or Upstream side¨. If you mean power in and power out it really doesn´t make a difference for DC circuit breakers. Current heats up the dashpot inside the breaker and trips either way.
    "Joint Venture" 1978 midcabin 28', twin 2017 Vortec roller cam "bullet proof" 383/6.3L full roller 350hp engines - You name it, I've either replaced it, restored it, rebuilt it, repainted it or repaired it. That's my job now that I'm retired.

    Comment


    • #3
      I didn’t expect downstream to be a proper electrical term, Bill! I was going for “descriptive.”

      The electrical power on the boat (other than the starter circuit and bilge pump) runs from the battery selector switch, through the 80-amp circuit breaker (that was installed before I got the boat), then on to the helm and other circuits. The battery selector switch, of course, determines which battery is the source of that power.

      The alternator B+ wire connects on the load side of that breaker. Since I understand the B+ wire is supposed to be carrying charging current to the battery(-ies), I find it odd that it would be connected on the load side of that breaker, rather than maybe on the common terminal in the battery selector switch, or on the battery side of the breaker.

      Yeah, it works fine. But is it skookum?

      Let’s say I had a major short in the helm circuit that caused that 80-amp breaker to trip while underway. Suddenly the alternator is not connected to any battery. I’ve heard that will toast an alternator in short order (which is why one should never switch the battery selector switch to “OFF” while the engine is running, eh?)

      However, if the breaker tripped in that situation and the B+ was connected to the battery side of that breaker, or to the common terminal in the battery switch, that alternator output wouldn’t be affected. That’s all I’m trying to confirm.

      The post-factory wiring on the Cardinal was done pretty well over all. But I have found a few areas that could be improved and am wondering if this might not be one of them.....
      -- Tim Taylor

      1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
      1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
      1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


      I wrote a song about a tortilla. Well actually, it’s more of a wrap.

      Comment


      • #4
        tim can you draw the circuit in question?
        1980 2400 Cuddy I/O, 2017 Cummins 4BT coupled to a Volvo DP-SM with F9 Props, and a 2014 Mercury 15HP Pro-Kicker "LOOSE CHANGE"

        Comment


        • #5
          Here are the main positive cable runs are they are at present.

          Starter Battery runs to the #1 on the selector switch.

          House Battery runs to the #2 on the selector switch.

          Common off the selector switch has two cables. One runs to the starter. The other runs through the 80-amp circuit breaker and on the boat's loads.

          The B+ cable off the alternator connects on the load side of that circuit breaker.

          My plan is to connect it to the lower, supply side of that breaker along with the Common cable coming from the selector switch.

          Result would be the same, except that the B+ would still have someplace to go in the event the breaker tripped.



          My only question is that someone who ostensibly knows about Marine DC wiring set it up this way, so I wanted to run this by the Glasply Brain Bank first to make sure I wasn't missing something!

          Thanks.....
          -- Tim Taylor

          1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
          1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
          1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


          I wrote a song about a tortilla. Well actually, it’s more of a wrap.

          Comment


          • #6
            that is very strange, personally, i have my alt output wire goes to a 80 amp circuit breaker strait to the main starter terminal, amperage of the circuit breaker depends on the alternator output
            1980 2400 Cuddy I/O, 2017 Cummins 4BT coupled to a Volvo DP-SM with F9 Props, and a 2014 Mercury 15HP Pro-Kicker "LOOSE CHANGE"

            Comment


            • #7
              how many wires are on the alternator? or is it internal regulated
              1980 2400 Cuddy I/O, 2017 Cummins 4BT coupled to a Volvo DP-SM with F9 Props, and a 2014 Mercury 15HP Pro-Kicker "LOOSE CHANGE"

              Comment


              • #8
                Originally posted by noluck View Post
                how many wires are on the alternator? or is it internal regulated
                There’s the B+ wire to the battery switch through the load side of that breaker as on the diagram and also an orange 8-gauge wire that disappears into the factory (Volvo Penta) harness which I believe ends up at the starter. Also off the alternator is a purple wire running I believe to the ignition.

                Mind you, that 80A circuit breaker is intended to protect the wires carrying the loads from the battery(-ies) to the various boat circuits. I do not believe it is there to protect the cable coming off the alternator.
                -- Tim Taylor

                1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
                1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
                1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


                I wrote a song about a tortilla. Well actually, it’s more of a wrap.

                Comment


                • #9
                  Tim - I agree with your assessment. The charging wire from the alternator should go to the same side of the breaker as the battery switch is wired to. As shown in your diagram, there's no overload protection between the alternator and distribution panel.
                  They civilize left, they civilize right, 'til nothing is left and nothing is right. (Ben Rumson)

                  Comment


                  • #10
                    Originally posted by Arne K View Post
                    Tim - I agree with your assessment. The charging wire from the alternator should go to the same side of the breaker as the battery switch is wired to. As shown in your diagram, there's no overload protection between the alternator and distribution panel.
                    100% correct Tim.
                    "Joint Venture" 1978 midcabin 28', twin 2017 Vortec roller cam "bullet proof" 383/6.3L full roller 350hp engines - You name it, I've either replaced it, restored it, rebuilt it, repainted it or repaired it. That's my job now that I'm retired.

                    Comment


                    • #11
                      Thanks, guys. I’ll get that swapped around.
                      -- Tim Taylor

                      1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
                      1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
                      1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


                      I wrote a song about a tortilla. Well actually, it’s more of a wrap.

                      Comment


                      • #12
                        On my Mercruiser B+ from the alternator connects to the starter, which is switched power from the main disconnect, from the starter is a #10 that provides a 50A circuit. for the engine.
                        It does not look right in your drawing, seems it should hook directly to the battery or preferably the switch or the starter.
                        Suspect VP and Merc did things different, has to be a VP wiring diagram.
                        1982 2580 "HI-BOY " IN 2 DEEP 5.7LX ALPHA

                        Comment


                        • #13
                          Turns out there is still the factory B+ wire as you describe. Go figure. Someone added the other wire and attached it to the House side, perhaps to make sure both batteries received a charge regardless of what position the battery selector switch is in.

                          I am in the midst of a *complete* upgrade of the entire electrical system, replacing all the battery cables with bigger, proper ones. Also replacing the selector switch with a OFF-ON-Combine switch along with an automatic battery isolator that will allow a charge to either battery needing it. I’ll be running that extra B+ cable to the starter battery POS terminal in the process. Stay tuned.....
                          -- Tim Taylor

                          1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
                          1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
                          1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


                          I wrote a song about a tortilla. Well actually, it’s more of a wrap.

                          Comment


                          • #14
                            The acr from blue seas works very well and saves the hassle of trying to remember to turn the switch to save the starting battery. I did add a aux light at the helm so i could tell when the batteries are combined. Blue seas has a very very tiny one that i couldn't see in daylight, bought a bigger one. It only stays on when charging.
                            1982 2580 "HI-BOY " IN 2 DEEP 5.7LX ALPHA

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