1. Untitled Document

Battery and 12V Wiring

Discussion in 'MOTORHOME CHAT' started by CJB, Jun 18, 2013.

  1. CJB

    CJB Funster

    Joined:
    Feb 26, 2013
    Location:
    Kent
    Morning all,

    I am going to be fitting a Solar Kit to the MH and also adding a second battery to create battery bank, I have a few questions that I hope some of you can help me out with.

    1) Does the second battery in the bank have to be the AMP rating at the first?

    2) When connecting the two batteries what gauge cable should I use?

    3) When connecting the solar charge controller to the battery bank am I correct in thinking that you connect the positive to one of the batteries and the negative to the other to ensure even charging?

    4) The MH battery charger is currently connected to one battery do I need to connect this across the two batteries as mentioned in point 3 above to ensure proper charging?

    Any advice most welcome :Smile:
  2. pablomc

    pablomc Funster

    Joined:
    Apr 20, 2010
    Location:
    Co. Durham
    Hope this helps.

    1) Does the second battery in the bank have to be the AMP rating at the first?
    No, but it must be the same type e.g. if your existing battery is SLA (sealed lead acid) then you should use SLA. If your existing is Gel then you would need a Gel etc. Depending on the age of your existing battery it is sometimes good practice to replace both. Why not look at a couple of decent traction batteries since you are looking at changing. :thumb:

    2) When connecting the two batteries what gauge cable should I use?
    Depends what you going to use them for. If you are using an inverter then the cable should be suitable for the load. If you are just running standard equipment then look at the existing cable thickness. If it is 6mm then use 6mm (assuming the batteries are to be co- located), If the existing is 16mm then use 16mm etc.

    3) When connecting the solar charge controller to the battery bank am I correct in thinking that you connect the positive to one of the batteries and the negative to the other to ensure even charging?
    It is good practice, but not essential for two batteries as long as you maintain a parallel and not serial connection between the two assuming 12 volts)

    4) The MH battery charger is currently connected to one battery do I need to connect this across the two batteries as mentioned in point 3 above to ensure proper charging?
    Again good practice, but not essential for two batteries.
  3. SomeoneElse

    SomeoneElse Funster

    Joined:
    Apr 22, 2013
    Location:
    Cotswolds
    Do you really think this is within your abilities?:Blush:
    Batteries contain a lot of energy, release it wrongly and there will be some big sparks and a lot of heat. If your not sure wear googles, welding gloves and fire proof clothing.

    To answer your questions:
    1. In an ideal world the batteries should be identical, right down to the manufacturer's batch number. In practice make sure the battery technology is the same. IE if you have a gel battery buy another gel, the same with AGM, flooded, maintenance free etc. size is not so important.
    2. The cable size must be suitable for the intended load, if you aren't going to increase the load use the size fitted by the manufacturer of the motorhome as a minimum. The import thing is to connect positive on one battery to the positive on the other, and to connect negative to negative.
    3. The positive output of the solar charge goes to the positive, with negative to negative as in two. The batteries with balance the charge via the inter-connecting cable.
    4. Same as 3.

    Now re-read my initial warning.
    Gordon
  4. jollyrodger

    jollyrodger Funster

    Joined:
    Oct 1, 2012
    Location:
    Plymouth
    Hi

    This is my set up which works for me but may not work for others.
    So: 80w solar panel>>
    30amp charge controller
    2 x 115 amp AUX Batteries>>
    “Ring” 1000w modified sine wave inverter.

    1 aux battery is charged from the engine when mobile.

    2nd aux battery charged by the solar system constantly

    I have an isolation switch between the two batteries, separated when mobile,
    and connected when parked bringing both batteries into play charged from solar system.
    a very simple manual set-up.
    No doubt there are devices and other methods that will do maybe a better job, but including the batteries, solar system, inverter, and switches, (I also have an isolator on the Inverter as they will drag a battery down even when off) the whole lot came in at just over £350 NEW that’s including a tube of sikaflex brackets, roof gland and cable .Stratford at the moment with not a lot of sun and running the laptop from the inverter, batteries are showing 13.2v
    As for the type of cable I’ll leave that to the “professionals” me I used 30amp flex :Wink:
  5. mitzimad

    mitzimad Funster

    Joined:
    Jan 28, 2008
    Location:
    walthamstow east london
    Another vote for traction batteries ive got 2 6v 225amps trojans and they are great but they do need to be checked for liquid levels from time to time

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