Batteries linked in tandem

Discussion in 'Tech/Mech General' started by cyclingdoglucy, Sep 20, 2009.

  1. cyclingdoglucy

    cyclingdoglucy Read Only Funster

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    this weekend i fitted a second battrey to my motorhome to give me more capacity when out in the fields,but the more experienced owners are saying to me that i should have replaced both battreys as the older of the two battreys would quite quickly destroy the new one. there was nothing wrong with the original battrey ?, i just wanted to last a few days longer. i would like any advice on this ,& yes i will replace the first battrey if you think i should ?. thankyou:Smile:
     
  2. slickmouse

    slickmouse Read Only Funster

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    Short answer NO
     
  3. DESCO

    DESCO Read Only Funster

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    It is normal accepted practice to replace both I personally would but it is up to you, I was always taught that the old battery could pull down the new.



    Dave:thumb::thumb:
     
  4. Larrynwin

    Larrynwin Funster

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    Thought this thread was for ELECTRIC BIKES :Rofl1::Rofl1:
     
  5. JayDee

    JayDee Funster

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    Paralleling batteries

    Hello clever people,
    From reading on here and elsewhere I gathered that accepted wisdom was to parallel two batteries of the same size and type, of the same age with a fuse (how big??) in the positive link cable.

    I was discussing this with a (non-motorhoming) friend of mine and he believes that any discrepancy between the internal resistances of the batteries would cause the lower to charge at the expense of the higher. This sounds logical, but does it matter? Wouldn't the higher resistance battery charge up when the other had reached full charge? My mate thinks it would matter.

    I don't have a clue. Do any of you?

    Also.... Gel batteries; are they worth the huge amount of extra cash. The leisure battery is inside the cab under the passenger seat.


    Thanks for any help

    John
     
  6. Tony Lee

    Tony Lee Read Only Funster

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    There is a fair bit of mumbojumbo regarding batteries and a lot of it can be safely ignored when life and limb is not an issue. Yes, hooking up and old battery with a new battery may result in you getting less that 100% out of the new battery and there may be other inefficiencies but provided they are both the same sort of battery - same brand and model is even better - you should get the extra free-camping time you need without wrecking anything.

    Keep an eye on it and if it seems as if the combined capacity has reduced then just connect each one in turn, charge it and see if it is holding a charge or not.

    For safety (and regardless of whether the batteries are new or not since even brand new batteries can fail), you should consider putting a fuse in the positive lead of each battery so that if there is a major failure of one battery, one or both will be disconnected.
     
  7. JayDee

    JayDee Funster

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    Knowledge quest

    I'm still unsure.

    The fuse in the positive side of the link cable - what rating should be used?

    The issue with the difference in internal resistances - is that important? Will it affect the overall performance? Or worse, cause early deterioration of one of the batteries?

    Other than the fact you can turn them upside down, is it worthwhile forking out a bank loan for Gel batteries or, as long as they're sealed to atmosphere, is there anything wrong with the more conventional Lead Acid?

    Questions, questions, nothing but questions.:RollEyes:


    John
     
  8. welsh winger

    welsh winger Read Only Funster

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    Fuse rating

    Hi I have just fitted a second leisure battery, using a brocott split charge, same as the one in this link.
    SPLIT CHARGE RELAY KIT- 12V 30AMP SELF SWITCHING on eBay (end time 23-Sep-09 15:43:56 BST)

    The kit comes with a 20amp fuse, apparently each battery pulls 10 amps when first connected for a short period of time, which also answered my second question, which was, could I charge 2 battery's from the same split charger unit, the answer was yes but up the fuse to 25 amps, he then went on to say it would be better to use a split charger for each battery, this was after prompting from me rather than the seller trying to sell 2 units, his reasoning was you would need 2 new battery of the same type for it to work successfully.

    The theory behind this unit is the first battery has to reach a set voltage, before the unit starts charging the second battery, I seem to think it was 13.2 volts.

    Hope this bit of info helps.

    Nick
    Welsh Winger
     
  9. JayDee

    JayDee Funster

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    It does indeed, Nick.
    Do you mean that for the one split charger to work with two batteries they would need to be new and similar, or do you mean that they would need to be new and similar if using a second split charger for the second battery. I assume the former as this bears out what my friend was saying. I guess that if you're running each battery on its own split charger it doesn't matter what the size, type and condition is.

    Sounds useful. Thanks very much. :thumb:

    Now all I need is a bit of expert-but-impartial advice about the pro and cons of the gel batteries.:Smile:


    John
     
  10. welsh winger

    welsh winger Read Only Funster

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    They need to be new and similar either way, but I was recommended to use 2 split chargers.

    I looked it to gel battery's, I decided that for the use I was going to put them too that ordinary lead acid would do the job, we go away for 4/5 days at a time, of course nothing to do with the cost:BigGrin:

    Nick
    Welsh Winger
     
  11. Reallyretired

    Reallyretired Funster

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    I have used batteries of different ages in the past without problem, but not with one that was really old as a significantly higher internal resistance could lead to very little charge going to that battery. For the same reason the two batteries need to be as close together as possible with short thickish cables.I have just installed a second battery on my van and as the old one needed replacement I have bought two the same (110Ah). The fuse is for safety if there is a short etc and so it just depends on what you think will be going in and out. I have fitted a 30A fuse though I would think 20A would be fine. Charging rate will depend to some extent on how far your batteries are from the alternator/charger and how heavy the cable is as if they are at a low charge and under the bonnet they could get up to a 50-60A charge initially. Stuck right up the back as mine are, no chance. I have seen suggestions of using an in line resistor of just a few ohms to limit the charging rate, however in my case the length of the cable probably does the trick. I had a gel battery in my old van, seem to last longer though the charging rate is restricted compared to the standard battery, as you say a lot more expensive.
     
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