Second Leisure battery

Discussion in 'Tech/Mech General' started by Allanm, Sep 19, 2013.

  1. Allanm

    Allanm Funster

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    I have a second leisure battery that I have fitted to my MH. I have seen a couple of different ways to wire these up in parallel and wanted to know if what I had done was correct. Cant believe I spent 18 years working at BT with huge banks of batteries that caused me no problems, now, it seems, there are "better" ways of doing things!
    So, I have 2 x 105 amp batteries, sitting side by side under the offside side facing sofa, both in secured battery boxes and breathing through a tube through the floor. Both batteries ( same type and size) have clamp and screw terminals. I have connected the second battery neg lead( clamp) to 1st battery ( screw terminal)
    Pos lead from second battery ( clamp) to first battery (screw terminal) via 25 amp fuse and holder. Both leads are about a foot long and about 2mm multistrand cable ( from my old BT batteries) First batt pos then goes via another 25a fuse to the van 12v wiring
    Is this correct? I have seen diagrams that suggest the pos lead from batt 2 goes to the van wiring via a 25A fuse and 1st battery's Pos terminal is connected to this via a 25A fuses. So, 3 fuses in all. Does this make sense?
    Allan
     
  2. mitzimad

    mitzimad Funster

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    im no electrician but the cable sizes and fuses seem undersized to me a discharged battery will draw as much current as the alternator can provide
     
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  3. Allanm

    Allanm Funster

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    Sorry, thats a typo, cable size is 5mm, which is bigger than the original cables and fuse is the same as the original inline fuse, so i am not bothered about them, its the method of linking them that got me wondering.
    Allan
     
  4. tonytange

    tonytange

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    No no no do not connect the battery's this way it will output at 24 volts and blow up your electrical units lights etc for 12volts connect +to+ - to - the - going to earth use a fuse no more than 20%above the Max output input you need
     
  5. pappajohn

    pappajohn Funster Life Member

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    easy........positive from one battery ALWAYS goes to positive of the second, or as already said...you get 24v.

    connecting the main van 12v supply wires to either battery, or even pos of one and neg of the other if access is awkward, will give the same results.

    if the inter-battery leads are short and direct then only one fuse will be needed in the pos wire....if the batteries are quite far apart, or the link wire could chaff and short to earth, then 2 fuses are recommended as in the attached image.

    cross wiring only really works if you have 4 or more batteries then its a minefield of different configurations.
     

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    Last edited: Sep 19, 2013
  6. Allanm

    Allanm Funster

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    They are connected in parallel as I stated at the start of my post, so no worries there.

    PJ, both cables are only about a foot long and both go inside the plastic battery boxes, no metal or anything else to chafe so I have fitted only one fuse ( batt 2 on your diagram), but I can see your reasoning and I will fit a second fuse on the other end of the + wire at Batt 1. Referring to your diagram, I also have a fuse between 1st battery + to hab 12v.
    Thanks all
    Allan
     
  7. Techno

    Techno Funster Life Member

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    35mm no fuses
    [​IMG]
    [​IMG]
     
    Last edited: Sep 19, 2013
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  8. Allanm

    Allanm Funster

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    Nicely over engineered. I like that.
    Allan
     
  9. mitzimad

    mitzimad Funster

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    thats more like it should be
     
  10. tonytange

    tonytange

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    Sorry Alan gess I didn't read your post correctly jumped to wrong conclusion
    Tony
     
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