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Thread: Dual Battery Setup Help

  1. #1
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    Default Dual Battery Setup Help

    Okay guys. I have never setup a dual battery system, so I need a little advice.

    To start off, I have a Ford Ranger and room under the hood is limited. So I want to put the 2nd battery behind the driver seat in the extended cab. From there I would like to run power into the camper to a circuit block. (http://www.sierraexpeditions.com/ind...t_detail&p=550)
    As for the isolator/combiner I am planning on using the National Luna since it seems to be very popular here.

    Some questions that I have are:

    1. What gauge wire do I need running between the batteries/isolator?
    2. What gauge running from battery 2 to the circuit block?
    3. Do you recommend any other isolator/combiner?
    4. Do you recommend something other than the circuit block?
    5. Any overall advice?

    Thanks guys!

  2. #2
    Quote Originally Posted by anchorshot View Post
    Okay guys. I have never setup a dual battery system, so I need a little advice.

    To start off, I have a Ford Ranger and room under the hood is limited. So I want to put the 2nd battery behind the driver seat in the extended cab. From there I would like to run power into the camper to a circuit block. (http://www.sierraexpeditions.com/ind...t_detail&p=550)
    As for the isolator/combiner I am planning on using the National Luna since it seems to be very popular here.

    Some questions that I have are:

    1. What gauge wire do I need running between the batteries/isolator?
    2. What gauge running from battery 2 to the circuit block?
    3. Do you recommend any other isolator/combiner?
    4. Do you recommend something other than the circuit block?
    5. Any overall advice?

    Thanks guys!
    1. The thicker the wire/cable you use, the better the recharging performance will be. 8 awg minimum. Also add another wire from alternator (+) stud to isolator's engine battery side. Use thick ground wires too.
    2. Depends on the maximum loads you plan on running through the circuit block, and the Distance from battery to circuit block. Again, 8 awg minumum, imo.
    3. I use a manual 1/2/both/off switch, but I'd recommend a simple 35$ dumb solenoid rated for at least 100 amps continuous. Google continuous Duty Solenoid. I think the Smart solenoids which operate on a delay or voltage setpoint just open the door for more problems and higher replacement costs.
    4. Use whatever you can to keep the wiring organized and safe.
    5. A. Use an AGM battery in your proposed location. A flooded battery needs to be in a sealed box, vented to the exterior. Technically An AGM battery should too.
    5. B. You will not save money by buying a cheap battery, unless you can kill it within the free replacement warranty period. The pro rated warranties are a joke. Know the difference between Starting batteries Marine/dual purpose/RV/trolling/"deep cycle" batteries, and true Deep cycle batteries. Get the one which will apply most to your situation.
    5. C. look into installing a battery under the battery by the frame.with something like this:

    [ame="http://www.amazon.com/gp/product/B002Y33602/ref=pd_lpo_k2_dp_sr_2?pf_rd_p=486539851&pf_rd_s=lp o-top-stripe-1&pf_rd_t=201&pf_rd_i=B001O0D6R4&pf_rd_m=ATVPDKIKX 0DER&pf_rd_r=0P9E9VF3Z18APY518Z1Z"]http://www.amazon.com/gp/product/B002Y33602/ref=pd_lpo_k2_dp_sr_2?pf_rd_p=486539851&pf_rd_s=lp o-top-stripe-1&pf_rd_t=201&pf_rd_i=B001O0D6R4&pf_rd_m=ATVPDKIKX 0DER&pf_rd_r=0P9E9VF3Z18APY518Z1Z[/ame]

    If you cannot easily water the battery, get an AGM.
    Last edited by wrcsixeight; 11-22-2010 at 01:23 AM.

  3. #3
    Join Date
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    Lower Slobbovia (Mariposa)
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    I used these wire charts to determine diameter based on length: http://www.rbeelectronics.com/wtable.htm

    Best advice: Completely understand everything you are doing before you buy anything. What current is being pushed through, what accessories you may be running and their current requirements, When you think you have it all figured out, give yourself a week or two and you'll come up with more questions.

    Here's some camper setups: http://www.hellroaring.com/rv.php

    Use Ohm's Law to see how much current your accessories require. You know the voltage, the accessory will indicate the wattage, find current (amps): http://www.ohmslawcalculator.com/ohms_law_wheel.php
    Last edited by keezer37; 11-22-2010 at 07:03 PM. Reason: add diameter
    Keezer
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  4. #4
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    I don't understand the solenoid. What I picture in my mind is this:

    A wire going from the starting battery to the solenoid. From the solenoid to the 2nd battery. Then a wire from the solenoid to a switch that I can manually turn off/on or combine/isolate. And then a ground from the solenoid as well.

    Is there anything like this? I would rather turn it on/off myself rather than it turning on every time I run the truck.

  5. #5
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    I always use 12 volts when doing the calcs. A battery puts out more than that when charged and a charging system puts out even more voltage than the battery (it has to or it couldn't charge the battery). By using 12 volts rather than battery or charging voltage it means that the amperage draw is higher for the same wattage, and that automatically makes cable size choices erred on the safe side.

    I have a marine spec VSR (BEP Marine) backed up by a marine battery combining switch. I do not expect to have a problem with the VSR, but if I do I can use the marine combiner switch as a manual back-up. Having used the simpler continuous duty solenoid in the past I do prefer the idea of the primary battery getting fully charged first before the solenoid brings the secondary battery into the charging circuit.
    Last edited by ntsqd; 11-22-2010 at 03:47 PM.
    I used to swerve around my hallucinations, now I drive right through them.

  6. #6
    Quote Originally Posted by anchorshot View Post
    I don't understand the solenoid. What I picture in my mind is this:

    A wire going from the starting battery to the solenoid. From the solenoid to the 2nd battery. Then a wire from the solenoid to a switch that I can manually turn off/on or combine/isolate. And then a ground from the solenoid as well.

    Is there anything like this? I would rather turn it on/off myself rather than it turning on every time I run the truck.

    The solenoid only switches the (+). There are 4 teminals on a dumb solenoid. 2 big studs, and two little studs.
    One big stud is wired to the engine battery(+)
    One Big stud is wired to the accessory/ house battery.

    The two other connections, when they see 12 volts from any source you provide, be it a manual toggle switch, or a wire from the ignition, or from any fuse which is hot only with the engine running, when it sees 12 volts, it connects the 2 batteries. You ground the second battery back to the first battery, or right to the frame or engine. The ground(-) is common to both batteries. There is no switching of the ground.

    My comment about running another wire from the Alternator (+) to the engine battery side of the solenoid is to augment the undersized stock vehicular wiring, and greatly increase the current the batteries can ask for from the alternator. And upgrading the grounds from batteries to frame/engine is the other half of the improvement necessary to see maximum alternator recharging amperage.

    You can also get a manual boat battery switch like I have


    But I think a quality Dumb solenoid, activated by a dashboard mounted lighted toggle switch is a more elegant solution, and would be how I would do it in my Van if I had it to do over again. I'd also like voltmeters for both batteries.

  7. #7
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    Both ground cables need to go to the same bolt or stud.

    Manual control is great until you forget to turn it on, or off. Simple is good, but don't leave yourself a trap to fall into.

    A single voltmeter with a SPDT mon-off-mon switch will allow checking of battery voltages w/o the meter itself being a constant draw.
    I used to swerve around my hallucinations, now I drive right through them.

  8. #8
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    Quote Originally Posted by ntsqd View Post
    Both ground cables need to go to the same bolt or stud.

    Manual control is great until you forget to turn it on, or off. Simple is good, but don't leave yourself a trap to fall into.

    A single voltmeter with a SPDT mon-off-mon switch will allow checking of battery voltages w/o the meter itself being a constant draw.
    Recently installed the National Luna kit in my FJC and did not use the same bolt for the two ground cables. Why is this a problem?

  9. #9
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    When they are connected together and there is no charging system in operation the minute resistance between the grounding points will set up the see-saw discharge that paralleled batteries are so famous for. BT, DT had to buy new batteries twice before I figured it out. If this situation isn't common to your system then it may not be a problem, but why set someone up for failure when the solution is simple?
    I used to swerve around my hallucinations, now I drive right through them.

  10. #10
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    1980 Int'l Scout II Diesel
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