Charging setup for 2 leisure batteries

Discussion in 'Motorhome Accessories' started by gazza280, Jan 17, 2014.

  1. gazza280

    gazza280 Read Only Funster

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    Hi Guys

    This might seem like a newbie question but I need an answer.
    I have just bought 2 new 110amh batteries to put in the van to give me 220amh. I am replacing an old 110amh battery that came with the van.
    I am a complete novice with electrics but if I were to just replace the battery like for like there would be no problem because the setup is the same, but because I am adding another leisure battery, I am confused to how they charge.
    Normally on hookup I have the battery charger charging the batteries "starter and leisure" and when driving the van the alternator is charging the starter first then the leisure battery.

    Now I want to add another battery to the mix, so does the battery charger that I am using now still charge both batteries, independently, together or does only 1 of the leisure batteries get charged.

    Do I need a new charger to replace the one I already have do I need to put a split charger between the 2 leisure batteries?
    I have looked at possible solutions but there are so many I am totally confused. Aggghhh!

    Isolator switch, split relay, intelligent charger ie: ctek, sterling battery 2 battery charger?

    I like the idea of having an intelligent charger like the ctek because it checks the batteries at different stages to get the best from the batteries.

    Looking on google and youtube, the videos of people who have added extra batteries just hook the batteries together, in parallel of course, with not a charger or split charger in site.
    Now I know that if I'm going to get a definitive answer its gonna come from one of you guys, so much appreciation in advance, and remember I know very little about electrics.

    Many thanks
    Gary:thumb:
     
  2. tonyidle

    tonyidle Funster

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    If the two are close together (in the same compartment) simply do as you suggest & connect them together + to + and - to -. Use the same size cable as is used at present. If they are separated by being in different locations do the same but include a fuse at each end of the cable linking the +ve terminals. Use 50A fuses. Any charging arrangements will charge both batteries as if they were one. A smart charger is a very good idea if the existing charger fitted to the 'van isn't already a smart charger.
     
    Last edited: Jan 17, 2014
  3. Dolomite Pete

    Dolomite Pete Read Only Funster

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    Assuming the two batteries are close together and connected in parallel (put a 10amp fuse in positive wire connecting the two batteries), you should then arrange the power take off from the neg of one battery and the pos of the other. This minimises the losses due to internal resistance. I've done the same thing on my van recently. All of the original charging systems (driving and hook up) all work fine with out doing anything else.
     
  4. beachcaster

    beachcaster Read Only Funster

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    A solar panel will keep both batteries topped up.......and I also have one of those smart boxes that auto switches between topping up the vehicle battery and the leisure batteries.

    barry
     
  5. Steve304

    Steve304 Read Only Funster

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    :Eek!: Now I'm confused as well!

    Like the OP, this is something that I have considered doing as well but there is conflicting information from the two posts answering the question already.

    Are the batteries connected + to + and - to -, or as Dolomite Pete states above - to + and + to - ? Also, if they are located side by side in the leisure battery cabinet. Do they need a fuse?

    Please clarify if possible and thanks for your help.

    Steve
     
  6. gozomike

    gozomike Funster Life Member Life Member

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    For 2 12volt batteries always + to + and - to - anything else would result in a big bang. I am sorry I did understand what Dolomite Pete said and it is not what you suggest. If you do not fully understand it is best to get someone who does to do the connections.
     
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  7. phase3begins

    phase3begins Read Only Funster

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  8. TheCaller

    TheCaller Funster

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    I really must take the time to learn how to use a sketching program - a diagram would really help here.

    Let's assume that you have room to put the new battery right next to the replacement one. It's certainly better if you can keep them together.

    Let's call the replacement battery A & the 2nd new one battery B.

    Disconnect the negative terminal from your old battery first. Then disconnect the positive terminal, remove the old battery & put the new one (A) in position. Put battery B next to it.

    Now connect the positive terminals of both new batteries together, using wire of similar thickness to the existing leads. Then connect the negative terminals together. In effect, you have now created one big 12v battery.

    Now reconnect the positive lead to battery A, just as it was connected to the old battery.

    Finally, reconnect the negative lead, but if possible, don't connect it to battery A, connect it to battery B. This is the point Dolomite Pete was making. This ensures the load is equalised between the two batteries. If you connect both leads to battery A, it will always have to carry more of the load, because even a small voltage drop in the connecting wires will cause battery A to do more work. If you can't easily connect your negative lead to battery B, then use the biggest wires possible to connect the two batteries together, to minimise the voltage drop.

    When you consider that the voltage difference between a fully charged battery & a flat one is less than 2 volts, even when under load, then even a tiny voltage drop makes a big difference.

    Fuses

    Many people consider a fuse unnecessary if the batteries are next to each other. The further apart they are, the bigger the connecting cables should be (voltage drop again) & the greater the need for a fuse to protect the cable. A 10A fuse in the positive lead should be ok for normal 12v loads, but if you have an inverter, or anything else that could put a high load on the batteries, I would up that to maybe 40A.
     
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  9. TheCaller

    TheCaller Funster

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    Very true; that site is the absolute bible if you want to know how it should be done.

    Most of it is overkill for a two battery motorhome setup, but for emergency vehicles and marine applications, it's the place to be. Anyone with 3 or more batteries needs to read that site, even if they don't put it all into practice.
     
  10. Daedalus

    Daedalus Funster

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    Simple diagram of battery connections for a twin battery setup attached....

    Daedalus
     

    Attached Files:

  11. TheBig1

    TheBig1 Funster Life Member

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    battery load balancing and internal resistance is good in theory but unnecessary in practice with a 2 battery setup, especially if they are side by side

    keep it simple so you dont add potential failure points
     
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  12. pappajohn

    pappajohn Funster Life Member

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    as previously said by others.......a fuse at both ends of the pos wire.....the attachment explains why.

    fuse size is to be considered as well.

    if you use 20amp rated wire to link the two batteries you dont want 50amp fuses....in a fault situation the wires will melt before the fuse blows as the current carrying capacity of the wire is far lower than that of the fuse/s .
     

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    Last edited: Jan 17, 2014
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