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Need 12/24 volt trolling motor wiring advice

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  • Need 12/24 volt trolling motor wiring advice

    I bought a 2nd hand boat and I could use some help on wiring the batteries for a 12/24 volt trolling motor.
    The boat is 16' Alum., has a 40 hp Yamaha on it, and the trolling motor is a Motor Guide 756 Brute (56 lb) and is 12/24 volt.

    When I bought the boat the guy didn't know if the trolling motor even worked, said he didn't use it.
    He was in the military and the boat sat up for the last 14 months untouched, both batteries (cranking & trolling) were dead of course. He replaced the cranking battery before I bought it.

    I hooked the trolling motor up to the new cranking battery just to test it. It works, but only if the switch on the foot control is in the 24 volt setting. Doesn't work if it's in the 12 volt setting (Should it?).

    Now I plan to get a new trolling battery to add to the boat. My question is:
    1. Should I run the trolling motor off the 2 batteries (one being the cranking battery) to get the best out of the 24 volt trolling motor? And if so, how would I wire it for this set up?
    2. Would I be better off not trolling with the cranking battery also, just use the trolling battery alone. And if so, should I be conceared about the TM only works in the 24 volt setting? Will that hurt the TM?

    The TM seemed like it wasn't going at full power when I tested it on the cranking battery. Surely because I was only on 12 volts. How could I get it to work on the 12 volt setting if I decided to just use one battery to troll.

    My fishing days are not long ones and don't happen often, so battery run down on the cranking battery from trolling should never be a problem.
    The boat also had a dual (10) charger with it, so as long as I remember to plug it in both batteries would get charged.
    Also, if I ran a 24 volt setup, would this effect the running lights on the boat, blow them? (I assume if wired correctly it wouldn't).
    Thanks in advanced for any help, info, tips, links... If I left out and details that are needed just let me know.

  • #2
    Re: Need 12/24 volt trolling motor wiring advice

    You are confused about the battery setup. You NEVER want the starting battery serving trolling motor duty as you will be guaranteed to have a no-start condition at some point in. First, there is absolutely no need to run a 12/24 volt motor on 12 volts. Why they did this is with a 24 volt motor silly. If the motor runs on 24 volts, then install two deep cycle batteries wired in series. Feed 24 volts to the motor and go. Forget 12 volt operation. It serves no useful purpose. Your trolling motor has three wires from the plug to the motor. Red to black = 24 volts. Orange to black = 12 volts. There are several wiring systems for these motors and boats so we need more information on how your boat is wired. 1) how many wires run from the batteries to the motor receptacle. (Answer = 2, 3 or 4). 2) does your boat have a panel at the front with a 12/24, and/or RUN/CHARGE switch? Any other information regarding current wiring (details, details, details please) will help with this.


    • #3
      Re: Need 12/24 volt trolling motor wiring advice

      Appreciate the reply. I said 2nd hand but I'm the 3rd owrner.
      Before I took ownership of the boat it was wired up using both batteries for the trolling motor (only had two batteries total in the boat), but they were both dead (shot) so I wasn't able to check the TM the way it was set up.

      He only put in a new cranking battery before selling it to me, so I was left with the mess he gave me. He acted like he knew nothing about the TM so he wasn't any help on telling me how it was set up, wired. May have been the 1st owners doings?

      There are 3 wires (white, black, red) coming out of the foot control going to the plug. (The white wire is cut and doesn't tie into the plug). Just the red and black (2 wires) are in use from the TM.

      That plugs into a female plug mounted on a home made alum. plate. (no panel with 12/24 or R/C switch on it, it's all home made wiring job).
      The female plug has 3 wires coming off it: 2 wires (both 6 ga.), red and black that run back to the battery compartment. The third wire is cut short, leading no where (not in use).

      I guess the main reasons I would have wanted to use the cranking battery was to be able to run the TM at full 24 volts, And I didn't plan on buying 2 new batteries. And the spaace issue for a 3rd battery.
      Don't they sell Dual Purpose Cranking/Deep Cycle batteries?

      Not sure if I missed anything, couldn't think of anything else. Just let me know if so. Thanks


      • #4
        Re: Need 12/24 volt trolling motor wiring advice

        The 12 volt feature of your motor is now disabled since the white wire is cut. This leaves you with 24 volt operation only and that's fine. The white wire on the receptacle being cut further means your 12 volt option is disabled. Since you have no 12/24 or run/charge switch that simplifies the wiring but I still urge you to not plan on using the starting battery for your 24 volt troller. But if you want to run the risk associated with this then leave the starting battery wired exactly as it is. Run another #6 red wire from the POS terminal on the start battery to the NEG terminal on the new battery for the troller. The existing RED wire from the receptacle at the bow connects to the POS terminal on the new battery. PAY ATTENTION HERE: The BLACK wire from the receptacle at the bow connects to the NEG terminal of the START BATTERY. If you now measure across the two pin on the receptacle you should see 24 volts. Plug in the motor and go. If you don't see 24 volts you did not follow directions. There should also be a circuit breaker on the POS terminal of the new battery to protect the 24 volt system.


        • #5
          Re: Need 12/24 volt trolling motor wiring advice

          Thanks for the helpful advice!
          With the way you described hooking up the batteries, the 12 volt system (running lights) are perfectly safe correct? Also, just curious about when the main motor is running, it will still charge the cranking battery properly? (other battery also?)

          I've been reading up on the Trollbridge24 for my set up, sounds like it would be perfect for my needs. Any other thing like it on the market?

          Thanks for your patience and helpful advice! Much appreciated.

          Added: Just wired it as you described, tested the trolling motor and it has plenty of power. (running off 24 volts now of course)

          You mentioned a circuit breaker on the pos (+) going to the new TM battery, what size would you suggest it be?
          I noticed there is one on the neg (-) wire, the one that runs from the TM to the cranking battery. Looks like one of these in the link. Should I just use it, and switch it to the pos (+) wire on the trolling battery?


          Thanks again!


          • #6
            Re: Need 12/24 volt trolling motor wiring advice

            You are now getting into reasons why I suggest NOT to use the starting battery in a 24 volt system. NO! The engine cannot charge both batteries. It can only charge the one it is getting 12 volts from. You need an on board charger, preferably a two bank that you plug in at the dock. WARNING: Your lights and any other accessories currently fed from the STARTING battery must remain that way. If for any reason you try connecting them to the other battery (just moving the +12 volt wire from an accessory) you will be applying 24 volts to that device and it will fry. That includes the engine and its electronics. The circuit breaker in the negative line from the troller WAS necessary as it protected the 12V side of the 24 volt system. It is no longer needed. The wire size, the connectors, and the circuit breakers all must be able to handle the maximum current draw of the motor. So again, 56 amps is the worse case senario. You need a breaker at least that large but in a pinch you might get by with a 50 but not for long extended runs at the fastest speed. As for the TrollBridge 24, that will work only if you have a high output alternator. Since we have no idea what engine you have or what the alternator output is you have no guarantee this device will work for you. Keep in mind perpetual motion hasn't been invented yet. What I'm implying is that you cannot charge two batteries in a few short runs of an engine that has a 15 amp alternator. To put this in perspective, if you used the troller for one hour at wide open, it would consume 56 amps of power from the battery. With a 15 amp alternator you would need to run nearly four hours, wide open, to charge those batteries.


            • #7
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              Re: Need 12/24 volt trolling motor wiring advice

              Wow, that's a lot of good info, Thanks!
              I kinda already suspected that on the main motor not being able to charge the 2nd battery, was mainly making sure it would still charge the cranking battery without any problems. I mentioned in the 1st post that I have a dual 10 (amp) onboard dock charger, came with the boat. I would just have to make sure to plug it up when needed.

              I'll definitely be leaving the running lights on the cranking battery, was just making sure they would be fine. Got it now. And the main engine also, I didn't want to cause it any damage. I mentioned in the 1st post it is a 40 hp Yamaha, it's a 2 stroke. Not sure on the alternators output, but I wouldn't think it was much being it's only a 40 hp. So the TB24 may not be good for me.

              I wouldn't ever be using the TM on high for any extended time, as small as my boat is it would probably put it on plane.
              I'll get a new circuit breaker for the pos (+) side wire, the old one on the neg (-) is probably no where near close to a 50.

              Thanks again, appreciate it.