second battery

Discussion in 'The Beginner' started by pstockhi, Feb 13, 2010.

  1. pstockhi

    pstockhi Read Only Funster

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    Can anyone help I want to fit a second battery on my mh do I just take 2 leads from the battery thats there now or is there any other way to connect it and will it charge both batteries many thanks Peter:Eeek:
     
  2. peter marshall

    peter marshall

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    Hi Pete
    Yes run 2 leads from your battery to the same terminals ie plus to plus negative to negative a fuse on the plus is a good idea, both batteries will charge but if one is larger they will only charge up to the smaller battery level, better with both the same size. Pete:thumb:

    Ps just noticed you have a Chausson as well
     
  3. pappajohn

    pappajohn Funster Life Member

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    as peter said but fit a fuse in both ends of the pos wire as close as possible to the batteries....:thumb:
     
  4. dellwood33

    dellwood33 Read Only Funster

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    What type and size of fuse do you suggest & where is the best place to buy the necessary wiring etc.:Smile:
     
  5. nickhague

    nickhague Read Only Funster

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    frying tonight?

    Hi, best done with a split charger (£12 off ebay) and "tri rated" cable (auto leccy shop) with the cable rated to the distance and amps required to safely carry the current, otherwise fuses or no you will have your very own heated electrical cables running under/in your motorhome :(

    as a guide 6mm squared will pass a secondary charging current safely about 3 metres, above this go for 10mm sq, tri rated is the fine stranded copper cable, dont be tempted to use more solid "domestic" type stuff.

    without a split charger your primary battery will try to pull power from your secondary through your woefully small "jumper" cables thus creating heat.......the rest you know?
    also a split charger stops you draining your starter battery......

    also avoid the so called "leisure" battery if you can, get wise go "semi traction" aka L16, i bought a "Crown" brand 130 Amp hour battery for £100 from a retailer in Exeter, it will outlive a leisure 4 fold.

    when designing DC remember that much bigger and higher rated cables are needed to safely transfer power without creating heat, fusing at source and termination is also wise, hope this helps?
     
  6. Terry and Nicola

    Terry and Nicola Read Only Funster

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    leisure" battery

    HI ALL :Smile:
    I fitted a 2nd leisure battery i got some 6 mm wire from a mate and fitted one inline fuse got it from halfords it was £10 and 30 amp fuse was £3 it was on radio stand bit there was 2 in a pack just do not push the fuse in to hard cos i broke one when i pushed it in. I also fited an 500 wat inverter and a twin socket from it in the motorhome .:thumb:
     
  7. pappajohn

    pappajohn Funster Life Member

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    i use 50 amp wire and 30amp blade fuses.

    the reason for two fuses is.....

    if you fit one fuse only close to one battery and the connecting wire rubs and shorts to earth then the fuse at the one battery will blow BUT as the other end of the wire is still connected to the second battery then that end of the wire is still live and touching to earth...result...FIRE!!!!!

    motoring shop is a good place but not halfrauds....unless the wire and fuses are wearing a hoody and have acne, the children (salesperson) in there wont have a clue what you intend doing.
     
  8. Terry and Nicola

    Terry and Nicola Read Only Funster

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    motoring shop

    HI
    I did go to my local motoring shop but was not help and only had 3 amp wire and the in line fuse there had was only 3 amp wire on it but you are right it was a youg lad who helped me and i hate to say it he had more idea then i did . :thumb:
     
  9. pappajohn

    pappajohn Funster Life Member

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    next stoip will be a caravan dealers shop.

    i got my 50a wire at wardby's, south cave, humberside but any dealers shop will sell it.

    if you cant get an inline 30a blade fuse holder the just crimp/solder a couple of blue 'spade' connectors to the wire ends and push them onto the fuses lugs unsuring any exposed metal is covered/taped.

    i really cant believe they only had 3amp wire though....thats only 36watts.

    the 'boyracers' use massive wire on the giant 2/300watt amplifiers and boomboxs in their car boots.
     
  10. nickhague

    nickhague Read Only Funster

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    Hi, again, i cant over emphasise just how important it is to use either a split charger or a DC disconnect, picture if you will how much smaller (and longer) your leads are from your primary battery to your "leisure" battery as compared to your primary battery to starter motor leads are.

    Without a "one" way switch your starting battery will attempt to draw starting current amps not only from itself but from your secondary battery.......through your 6mm leads, result ? heat and a reduction from then on of those leads to "pass" charging current to your secondary battery, ultimately leading to a possible fire (but hey arent insurance companies understanding these days?) or just a terminal degredation of the system you installed.

    Need more? another reason to "isolate" the two batteries is this : two 12 volt batteries wired in this way are regarded to be in parallel, usually containing 2 very different types of battery (1 for starting, 1 for deep discharge/low current, ie leisure), these 2 types of battery have differing chemistries and amonst other things differing voltages "at rest" or no load.
    2 batteries wired in this way without isolation will constantly attempt to "homogenise" voltages, thus discharging themselves.

    Another point worth mentioning is that the amp rating of a cable is dependent on many things, the length of the cable, the type of cable, where the cable is sited, voltage and whether its DC or AC current, generally for DC fine strand "tri rated" cable is a must.

    So to be helpful, where do you get this stuff? ebay is good if you know what you are looking for, alternatively autoelectrician supplies, or a good domestic electricians suppliers.
    for a basic system in a motorhome with 12 volt start and say a 110 amp hr leisure connected at less than 3 metres cable length 6mm tri rated is ok, more than 3 metres use 10mm, fuse at 25 amp at the starter battery end and again at 25 amp after the split charger,
    How do i know this stuff? i have 2000 amp hrs @ 48 volt running a pure sine 4kw inverter running my farm and i install similar setups for friends, hope this helps.
     
  11. dellwood33

    dellwood33 Read Only Funster

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    I only want to "Double Up" the existing leisure battery capacity :RollEyes::Smile: so that I can last a bit longer without EHU when we are in France in the summer :Smile: I presumed that was all the OP was asking about.
     
  12. pappajohn

    pappajohn Funster Life Member

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    A very useful post nick, :thumb:
    but in this instance we are discussing adding a second leisure battery connected to the original leisure battery...in parallel...double the Ah but still 12v....(assuming both batteries are the same Ah rating).
    not connecting to the engine battery
    hence no 'switching' is wanted or nesseccary, just a simple pos to pos (fused)...neg to neg connection.
     
  13. nickhague

    nickhague Read Only Funster

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    batteries

    Ah my appologies, long day digging the veg garden, the bit about homogenisation applies to what you are talking about though, the only way to properly double Amp hour in parallel is to buy 2 batteries of the same type from the same batch, think new wine old skins, self discharge from homogenisation can be 10% or more in a 24 hr period, or buy 1 bigger battery and have it stand alone, you can get semitraction up to 230 ah in one battery, Deta and others make em for floor polishers and fork trucks, better chemistry than these so called "leisure". cheers N
     
  14. pappajohn

    pappajohn Funster Life Member

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    no problem nick....i figured you'd either mis-read or mis-understood.

    new matched batteries are best but there are many thousands of folks using relatively old and new plus differing Ah rating batteries without problem, my self included....one x 2 year old 110Ah and two x 1year old 110Ah...same make.

    of course the lowest rated or oldest (if the same Ah rate) will dictate the overall Ah storage but many folks can live with that :thumb:
     
  15. pstockhi

    pstockhi Read Only Funster

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    Thanks every one for your help

    Peter:shout::thumb:
     
  16. pstockhi

    pstockhi Read Only Funster

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    :Eeek:Been out today playing with the mh and fitted second battery as advised including 2 fuses I checked that the lights worked and that the battery charger is charging is there any other test just to make sure all is working as should many thanks Peter:Eeek:
     
  17. pappajohn

    pappajohn Funster Life Member

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    thats it then....another happy funster with twice the battery power.

    only thing i can suggest....if the second battery is 'indoors' and has a vent tube then route the vent tube to the outside.
    a small hole in the floor and a squirt of silicon sealer to make the hole water tight.

    battery gas is highly flammable and if the battery starts to gas it can be very bad for your health and your van.

    battery gas + spark = explosion !!!!!

    even a fuse blowing is enough!!!!!
     
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