connecting battery's

Discussion in 'Tech/Mech General' started by freelanderuk, Sep 15, 2010.

  1. freelanderuk

    freelanderuk Read Only Funster

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    i have just had a 85amp battery replaced under guarantee, at the moment i have 2 85amp battery's connected each with their own connection lead and a 85watt solar panel , i have another 85amp battery that i took of the boat and have the room to store this and connect it up also to the MH,

    question is would i be better connecting them all together and just using 1 lead or connect 2 on 1 lead and the 3rd on the other lead ,
    what size cable to use if i connect them all together
    thanks
     
  2. madbluemad

    madbluemad

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  3. freelanderuk

    freelanderuk Read Only Funster

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    thanks, i have had a read of that but it does not really answer my question , would i be better connecting all the 3 battery's in parallel or 2 in parallel on 1 lead and the 3rd on its own lead ?
    thanks
     
  4. madbluemad

    madbluemad

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  5. scotjimland

    scotjimland Funster Life Member

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    Hi

    The longer the cable the bigger the volt drop, and if you have two batteries together and one further away there will be a charging imbalance.


    You will get the best performance if the are all connected together in parallel with short connecting cables.. or links.

    Use the same cable in all links and keep them as short as physically possible.. this will keep the volt drop to a minimum..


    hth

    jim
     
  6. Terry

    Terry Funster

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    Hi if you connect all 3 together then they will all charge at the same time ie solar / hook up and engine :thumb:Why would you want to separate one ? unless you think you need a e,emergency stand by :RollEyes: That would need a independent charger.
    terry
    Forgot to say use thick cables ( earth strap size if poss )with fuses and keep them as short as poss
    EDIT Jim beat me to it
     
  7. madbluemad

    madbluemad

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  8. freelanderuk

    freelanderuk Read Only Funster

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    thanks Jim
    the length of the links will have to be about 24" due to getting the battery's in and out of there storage ( back of an autotrail near where the spare wheel goes) all three battery's will be here so i will have leads from my MH panel to 1st battery 24"links to 2nd battery 24"links to 3rd battery , what size cable please and i understand that there has to be a fuse on each +ve


    i have 2 connector leads to the MH panel for 2 separate battery's, so was thinking 1 battery on 1 and 2 on the other
    thanks
     
  9. scotjimland

    scotjimland Funster Life Member

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    Yes, they need to be fused at both ends as per the drawing Jim posted.. I would buy fused battery terminals rather than in line fuses.. l

    You need 25sq mm flexible automotive battery cable ..
     
  10. madmick1945

    madmick1945 Funster

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    Buy a cheap set of jump leads and use that cable -less loss
     
  11. scotjimland

    scotjimland Funster Life Member

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    less loss ???

    cheap jump leads are probably only 16mm , and even cheaper plastic..

    this application requires 25sq mm automotive cable

    don't skimp on battery cables.. buy the right size and quality for the job , if you have any doubts about size use an on-line cable calculator such as AEI or seek qualified professional advice.
     
  12. freelanderuk

    freelanderuk Read Only Funster

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    i have just been reading about connecting up banks of batteries here http://www.smartgauge.co.uk/batt_con.html seams very informative , was thinking about using method 2 or 4 , whats your thoughts on this
    thanks
     
  13. scotjimland

    scotjimland Funster Life Member

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    Method two is the better .. it's how my four were connected on the RV

    as the author says ...

    It is simple to achieve but the difference in the results are truly astounding for such a simple modification.

    ps.. good link
     
  14. pappajohn

    pappajohn Funster Life Member

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    looking at the diagrams in your link i would put money on the first one being the most popular and widely used method even though the author says its just laziness or incompetence that would dictate this method.

    strikes me the author is a bit of an anorak and the actual difference in connection method wont really be noticeable.

    personally I'd connect all three pos to pos, neg to neg and allow your charger/solar to charge all three simultaneously.
    as others have said....a fuse at BOTH ends of each pos lead.
     
  15. scotjimland

    scotjimland Funster Life Member

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    It is the better way John, have a look at an electric fork lift battery , golf cart or any other piece of kit with cells / batteries and see how it's done .. check your own RV .. I bet it is connected as Method 2

    In Method 1, the batteries will not charge or discharge equally .. they won't give their best.

    ok, I grant you may not notice if you never use them to their full capacity, ie always on EHU ... but if you want the maximum performance and battery life .. Method 2 is far better.

    In a new install or rewire why would you choose to do it otherwise ?
     
  16. freelanderuk

    freelanderuk Read Only Funster

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    i have found where i can get the leads made up but can not find any fuse holders for 25sq mm cable or fused cable clamps, any ideas please
    cheers
     
  17. BobProperty

    BobProperty Read Only Funster

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  18. olley

    olley Funster

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  19. BobProperty

    BobProperty Read Only Funster

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    25mm and 40mm cable will take a lot more than 40amp. Need to do some calculating as to fuse sizes. Sorry but busy at present so quick reply.
     
  20. olley

    olley Funster

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    The idea of using much smaller fuse's than is necessary to protect the cable, is that it is to protect the battery's from each other. You only need a big enough fuse for the maximum likely habitation loads. For RV's the situation is different as they usually have a relay to allow the habitation batteries start the engine, so much bigger fuses are called for.

    Clive in his schematic shows 25amp fuses, but getting large cables sizes to fit in fuse holders of that size is difficult.

    Olley
     
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