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Wiring a 4 position switch for 12 and 24 volts - 2 battery system

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  • Wiring a 4 position switch for 12 and 24 volts - 2 battery system

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ID:	10831524 Hello fellow boaters. Need some advice on wiring a battery switch to accommodate my 87 sea nymph pike attacker with two batteries, 30hp Mariner and 24v trolling motor. I am looking at the 4 position Blue sea battery selector switch, and am trying to use it to isolate Both batteries in the off position for charging and to run both 12v system and 24v trolling motor in the “all” position. I have diagrammed it out and it looks like it will work. I’m not sure about the middle scenario - if there is any potential to damage anything if this position is accidentally selected. I appreciate any input this community can offer. I searched for hours on here and the net with nothing that looks like this... Happy boating!

  • #2
    My cursory observation is as follows:

    Diagram on the left will not deliver 24 volts to the troller. In fact it won't even run because there is no complete positive feed to the motor circuit from the battery on the left. The engine will charge the battery on the right but not the left. All accessory circuits will operate from the battery on the right.

    In the center diagram you have a serious issue in that the NEGATIVE terminal of the left battery is connected into the POSITIVE side of the engine charging system. You need to rethink that scenario.

    The right side diagarm presents a serious issue in that you are expecting the 12 volt charging system on the engine to simultaneously charge a 24 volt series system. This will not work. Follow the electrons. Start at the +12 volt point on the engine. Current flows to the switch, out the switch to the POS terminal on the right side battery. From there the NEG terminal to the fuse panel that then runs back to the POSITIVE output of the ENGINE via the switch. There is a similar problem with the left side battery in the 24 volt system. You cannot do what you want to do with that switch. You can only charge a two -battery 24 volt system from a 12 volt source with a two output charger that has isolated grounds. Outboard engines do not have that capability.

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    • #3
      Forget about the thought that an outboard will charge anything but the motor starting bat.

      With a 24V troll and outboard you need 3 bats. If you use the starting bat with the trolling motor then sooner or later your going to drain the bat so it can not be used to start the motor. Charge the toll bats at home with charger
      94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
      95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
      07 Seadoo GTX
      Merc Adults Only VP Adults Only
      G-Dad always said "First Liar doesn't stand a chance"

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      • #4
        Thanks for the input! I forgot to mention: by isolating the batteries for charging, I was actually talking about charging them at home with a trickle charger on each with a quick connect on each battery. The boat was furnished by the po with these 2 deep cycle batteries and wired with no battery switch, very similar to the scenario on the right, where the outboard and accessories run off + and - from the right side battery which is running a series wire from - on right battery to + on left battery - and trolling motor only is running with + lead on right battery and - lead on left battery. I was trying to avoid wiring up 2 on/off switches into the current set-up so I can achieve isolated home charging on each without disconnecting leads every time. My thoughts were to use the left scenario to run the boat/ob without trolling motor, use the right scenario to run trolling motor and use “off” when home charging. My worry was the middle scenario, maybe there is a way to lock out the switch to prevent a potentially damaging situation. So - my quandary is, Will left and right scenarios suit my needs without damage to components? I am not a fan of adding a 3rd battery just to kick over that little 30hp a few times per trip... Appreciate the advice!

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        • #5
          I am not a fan of adding a 3rd battery just to kick over that little 30hp a few times per trip
          There is a guy on here which uses a lawn mower bat to crank his over (doesn't weigh much). Another uses a jump start bat to crank the motor
          94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
          95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
          07 Seadoo GTX
          Merc Adults Only VP Adults Only
          G-Dad always said "First Liar doesn't stand a chance"

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          • #6
            In a pinch, most 30hp can be rope started. On a properly tuned motor, the pocket size jump start packs will provide quite a few starts. My son-in-law and I use one at car auctions as quite often the vehicle you are interested in has a dead battery. BAck in the day before electric start outboards had charging systems, a battery for 25 - 30 hp motor would last nearly all summer before needing a charge.

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            • #7
              Thanks for the input guys. I’m still not grasping why I need a 3rd battery. All the accessories: bilge, live well, gps, lights, and radio are going to need to draw 12v off one of the deep cycle batteries, how does adding a 3rd battery only for starting help? I would still need to use the deep cycle batteries in 12v and 24v to accomplish all I need on this rig. 30hp has a rip chord so if all batteries went dead, we still have a way to fire it up. Back to my earlier quandary, Will left and right scenarios suit my needs without damage to components - so long as I’m not relying on the ob alternator to recharge the batteries? I was hoping someone had success with a similar setup or a better way to wire up a two battery system for 12v & 24v with 1 switch. My other option is installing a on/off switch on the existing series bridge wire and another on all 12v + wires going to right + terminal. I’d rather have all in 1 switch if possible. Ah the fun of playing with boat wiring!

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              • #8
                I'm not a fan of the switch idea, unless it's just a heavy on/off switch to make and break the series 24V connection.

                Originally posted by JFoxman View Post
                [ATTACH=JSON]{"data-align":"none","data-size":"large","data-attachmentid":10831524**[/ATTACH] I am trying to use it to isolate Both batteries in the off position for charging and to run both 12v system and 24v trolling motor in the “all” position.
                Buy a dual bank isolated ground battery charger and you won't have to worry about disconnecting the batteries, or the switch. Just wire up the 0-12V battery to all your normal boat loads, then add the second 13-24V battery for the trolling motor. The series + to - connection between the batteries won't allow the batteries to drain each other, as in a parallel connection. Wire it up and leave it, just connect the charger to 120V when you get home.

                Another option is to add a Blue Seas 12/24 receptacle, and plugs. Receptacle has 4 connections for the two batteries to be connected independently. Trolling motor plug would be internally jumpered for 24V, and would series the batteries when the plug is inserted. Battery charger plug would be internally jumpered parallel, so when you plug the charger in, both batteries are paralled for charging.

                That said, I'm in the same camp as others with having a 3 battery system if running an electric start outboard and 24V TM, so you have plenty of battery for emergency situations: bad weather, medical emergency, etc.



                2001 Crestliner SuperHawk 1800, Mercruiser 140HP
                2007 Tracker 1436 jon boat, 7.5HP Force

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                • #9
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                  None of your diagrams will work, only one that can be used is on the left and it will only work to start the motor and run boat electronics.

                  This setup will do what you want without a switch, but keep in mind it will drain both bats when trolling. If both are drained to far, then there is a problem starting. In this setup the motor will charge the first bat when running, and connect a dual bank charger to recharge both

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                  94 Formula 27PC Custom 509MPI MEFI3 , B3 XR
                  95 Rinker 232 w/ 7.4L Carb 0F425011 B1 0F486471
                  07 Seadoo GTX
                  Merc Adults Only VP Adults Only
                  G-Dad always said "First Liar doesn't stand a chance"

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