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On-board charger question

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  • On-board charger question

    I am installing a a 24-volt trolling motor and an on-board charger in the next few weeks. There will obivously be 2 batteries for the trolling motor, but in addition I have 2 for the engine/electronics as well.

    Can I install a 2-bank on-board charger and charge both sets of batteries? I am thinking yes, but I may need to put a second A/B switch in for the charging circuit so both sets of batteries are parralell (12 volt circuits). Is there any easier way? Or am I better off going with a 3-bank charger?

    Thanks!

    Jon

  • #2
    Re: On-board charger question

    Rethink the plan. You cannot connect a "series" (24 volt system) with a 12 volt (parallel) system. You could with a three bank charger (two on the troller batteries) and the third for the starting and accessory batteries. But for those two you would need a means to "parallel" those two batteries but you implied that those were already on some sort of switch. There is another way to get by with a two bank charger but the issue will be that one bank is charging three batteries at once so one of the troller batteries will take three times (roughly) longer to charge than the other. What you would need to do is have a switch (which you apparently already have) to PARALLEL the starting and accessory battery. You would need another switch to connect that parallel pair to the first trolling motor battery in the string which is the one with ground cable connected to it and the jumper on the positive terminal. With the dual battery switch set to BOTH, and the transfer switch on, the first troller battery and the engine/accessory batteries are placed in parallel for charging. My suggestion however, is to leave the engine/accessory battery pair as they are as they don't get deeply discharged and are charged by the engine via the dual battery switch or ACR/VSR. Add the two bank charger for the two troller batteries. Anytime you try to combine a "parallel" system with a "series" system you run into potential grounding and shorting issues because of the "series" wiring. Be very careful in what you eventually do. Here is a diagram showing the difference between series and parallel wiring.



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    • #3
      Re: On-board charger question

      When you connect 2 batteries in parallel and remain 12v, under the diagram you posted, would you be OK hooking up a VHF and fishfinder to that system along with a 12v trolling motor?

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      • #4
        Re: On-board charger question

        12 volts is 12 volts. If the device you want to add runs on 12 volts of course you can connect it. You can use one 12 volt battery or a dozen 12 volt batteries in parallel and still have 12 volts output. But you were talking 24 volt trolling motor before. You can't power a 24 volt troller from a 12 volt source. You also said you have four batteries. So where are you heading with this?

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        • #5
          Re: On-board charger question

          Perhaps what you need is a battery Isolator. A battery Isolator allows one battery to be charged while another battery is being used and vice versa. It does the switching electronically and automatically. So you could charge one bank of batteries and then switch to the other bank.

          Of course the simple less expensive alternative is a manual battery switch. It does the same thing but not automatically.
          Ike
          New Boat Builders Home Page
          "Don't tell me that I can't, tell me how I can."
          https://newboatbuilders.org

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          • #6
            Re: On-board charger question

            Let's define what I asked, and when.

            On my 2000 Star, I had a 12v trolling motor that was connected with an isolator to get a charge from the ALT. I also had this battery on a GUEST, along with a 3rd battery I used for accessories on a GUEST, but these 2 batteries were not connected together in any method. The 3rd battery was my MAIN.

            I sold that boat.

            On my current resto, I haven't decided yet on 12v or 24v for the trolling motor. If 24v, I am aware that these 2 batteries would be dedicated for the trolling motor and any accessory would fry above 12v.

            My question was if I choose 12v and wire in parallel like your diagram, can I attach the accessories knowing my amp hours have increased? Accessories mean seldom ON VHF radio and bow mount fishfinder, only on when trolling motor is lowered with the attached transducer. All other accessories on the main battery.

            Another question. If you have a 12v24v trolling motor. What does the 24v hookup give versus a 12v hookup? More power/less run time versus Less power and longer run time?

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            • #7
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              Re: On-board charger question

              Suggestion: Don't even consider one of the older 12/24 volt motors for a number of reasons. One is the very long description it takes to get electrically challenged folks up to speed and to get the blasted things wired properly. There are so many ways these things were wired that I won't even offer diagrams unless you first firm a plan. The motor is designed to deliver full power on 24 volts so why on earth they gave it 12 volt capability is a mystery (other than to allow one to poke alone on 12 volts -- but then thats why trollers have a speed control). If you have the choice of of 12 volts, 12/24, or 24, by all means, for simplicity, go EITHER 12 volts only or 24 volts only.

              Lets cover some basics with parallel wiring. Unless you use an ACR/VSR or a dual battery switch, batteries wired directly in parallel will equalize -- meaning the weaker will always suck the life out of the stronger until the two are equal. If you use the boat frequently this is not an issue, nor is it a problem if both batteries are the same make, size, and age.

              When you have just two batteries, one of which will be used for starting, then the above is even more important. The key is that you want to avoid having a dead starting battery which can very easily happen with batteries directly wired in parallel. With a switch, VSR, or ACR the batteries can be isolated so the dead starting battery issue is avoided. With a dual battery switch you can run everything off both batteries, or either of the two. You can also charge both batteries from the engine simultaneously or either one individually. The switch also allows you to actually start the engine off either battery or both. So that system is the least expensive, simplest and most versatile. That system is of course, a 12 volt only system. If you go 24 volts for the troller, you are again looking at three batteries. Two for the troller and a separate starting battery. Develop a plan and I will likely have a diagram for it.

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