Dual Battery Wiring

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  1. #1
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    Dual Battery Wiring

    I'm currently fabricating a dual battery system for my truck. I have welded all the brakets for the new tray and fuse box (for my offroad lights) and have a second battery. I was wondering which wire that I have to splice into before going to the isolator. There are many wires coming out of the alternator and I have lost the instructions that came with the isolator to tell me which one. The rest of the wiring should be a walk in the park.

    Oh ya, I've got a Ford inline six cyl.
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  3. #2
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    I think if you're talking about which wires to hook the second battery up to I beleive you splice the same wires that come off the original battery. I'm only 99% positive. oh ya dont forget to ground that battery.
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  4. #3
    Registered User Dan's Avatar
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    Are you talking a battery isolator, a square or rectangular box with a bunch of fins on it and three or four terminals or are you talking a solenoid?

    Battery isolators are pretty much out these days, nobody uses them anymore, five to six years ago everyone and their dog had battery isolators, eventually they all burned out, since essentially all they are is a bunch of diodes that only allow the power to run one way.

    Which means you alternator can't sense how much voltage is in the battery and doesnt always work right, fun huh?

    Isolaters were invented so that batteries could be isolated from each other and therfore one would not draw the other one down. Then we realized that when the vehicle is running, one will not draw the other one down since the voltage from the alternator is higher than the battery voltage.

    So all we need to do is isolate them from each other when the engine is not running, since two batteries will not have the same voltage they will try to equalize, but they will never equalize and just kill each other . No need for an expensive isolator though, a $15 solenoid does the job just fine.


    Take the battery isolator and return it to the store you got it from, or go burry it in the desert and put in a solenoid. Get a continuous duty solenoid and put it inline with a couple battery cables to connect the two batteries and activate it with an ignition feed. Now you'll have two battery power when its running, and one battery power when its not running, so run your lights and stereo (as long as you dont have to turn the ignition on) and go ahead and kill the battery, you'll have a fresh one waiting to start the truck.

    Need more info e-mail me.
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  6. #4
    Registered User Dave Gio's Avatar
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    Re: Dual Battery Wiring

    Originally posted by Stephan
    I'm currently fabricating a dual battery system for my truck. I have welded all the brakets for the new tray and fuse box (for my offroad lights) and have a second battery. I was wondering which wire that I have to splice into before going to the isolator. There are many wires coming out of the alternator and I have lost the instructions that came with the isolator to tell me which one. The rest of the wiring should be a walk in the park.

    Oh ya, I've got a Ford inline six cyl.
    Do you have a 3 post or 4 post isolator?
    If its a 4 post ("A" / "1" / "2" / "E") I've done it before.

    Unhook the main fat wire from the alternator, run a new wire from the alternator to the A terminal, run a wire from "1" to the main battery, run a wire from "2" to the aux, and the "E" terminal is hooked up to a switched 12VDC source (ie, only gets 12+ VDC when the ign is ON).
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  7. #5
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    So I wired the stuff up- only took me two years. Anyways, a few months down the road, after the wiring, after a few 4x4 trips, she all went to hell. I gradually started loosing power in my main battery to a point that it wouldn't start my truck. This always seems to happen on the side of the highway and never on some grassy flowery trail. So before she died, my back Aux battery metered 16v and the front one metered 8v. Slight difference. I only figured I should check it out when I could smell the battery acid cause it had puked out everywhere. Mmmm 16volts must make things go kaa-bluey.

    So for this to happen, I guess the voltage regulator on my alternator (which tested ok) cannot tell what the battery voltage on the second battery is because of the diode?
    Last edited by Stephan; September 29th, 2004 at 04:37 pm.
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  8. #6
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    Make sure you wire the batteries in parallel NOT Series. If you wire them in Series you will run 24v and blow stuff up. Hook the batteries up + to + and - to - and have the + and - leads coming off of one battery.

  9. #7

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    gonna run two 6v deep cycles in series
    If you wire them in Series you will run 24v
    if it was 2 12 volts than it would be 24v in series

  10. #8
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    Originally posted by BRONCO_2

    if it was 2 12 volts than it would be 24v in series
    Didn't Catch that. Didn't say 2x6v in the Origonal Message so I assumed 2x12v

  11. #9
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    Originally posted by boss hogg
    ive been thinking of a way to run lots of storage for camping gonna run two 6v deep cycles in series mounted in the box of the truck ahead of the inner fenders.
    any brand of batteries reccomened?
    I believe that most golf cart batteries are 6v. Pretty sure that they are reasonable priced as well. That would be my recommendation.
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  12. #10
    Silverback sdillen's Avatar
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    To restate what Dan said, I simply use a continuous duty solenoid. I use a deep cycle as my "house" battery...replacing the stock starting battery. This is used to drive everything when the key is off, and is the one that'll run dead if I leave my lights on or winch 'til it dies. I use a starting battery as my second (disconnected) battery. When I switch to Optimas, they'll both be yellow tops.
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  13. #11
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    Are you using a deep cycle as a starting battery. I didn't think they worked well or for very long in a super high current demand situation as is in the case of a starter.
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  14. #12
    Silverback sdillen's Avatar
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    I've wired it so that when I turn the key to "on", the second battery comes online, therefore the starter is always running on both batteries in parallel.

    Having said that, I have also been running my "new" truck for the last 6 months with only the deep cycle battery. I just haven't gotten around to mounting the second battery tray yet. The wiring is ready to go...just no tray. I have had no problems that were "battery caused" as a result of running only a deep cycle battery (costco marine d/c bat...less than $70). I do have an issue in that my stock alternator doesn't keep up with the demand I put on it when it's hot out (the A/C pushes the current draw 'over the edge'). I have also not had the opportunity to try to start the truck when it's -15.

    A better alternator will cure my first problem and a round tuit will solve the second.

    My experience with marine deep cycle batteries (which was in a boat if you can imagine....) is that they work fine as a starting battery IF you don't need a really long crank cycle. We never had a problem starting a 2cyl marine diesel engine in the middle of winter without glow plugs using a regular old marine d/c battery. My truck starts MUCH easier than that engine did.
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  15. #13
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    Originally posted by boss hogg
    thanx for the solenoid advice
    that makes total sense the solenoid will allow power flow from .
    relying and a mechanical connection, using electricity to trigger it in an electrical system seems a little fishy, look into using a marine
    battery switch with 1, 2, both and off selections
    use a deep cycle batt for winching, lights, power inverters
    and a marine starting batt for your starter
    my 2 cents
    sami
    xj

  16. #14
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  17. #15
    Registered User Bronco Boy's Avatar
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    Originally posted by mattyg
    relying and a mechanical connection, using electricity to trigger it in an electrical system seems a little fishy,

    Kind of like how you start your vehicle every day.



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