Connecting two batteries

Discussion in 'Tech/Mech General' started by Southampton, Oct 2, 2013.

  1. Southampton

    Southampton Funster Life Member

    Joined:
    Dec 16, 2011
    Messages:
    511
    Likes Received:
    289
    Location:
    Hampshire
    Hi all,

    I have had two 110A leisure batteries fitted by the dealer, and when I look at the lead between the two (the + to + and - to - leads) the leads are very thin (about the same thickness as an iPad charging lead). I believe they should be much heavier duty and at the very least the same core diameter as the main charging lead already fitted. The dealer tells me these are the correct leads, but I have my doubts. I would just like confirmation or not from you experienced guys.

    I will change them myself but at the moment it is a matter of principle having paid good money for the batteries and the fitting. So please tell me I am either right or the dealer is right.
     
  2. tonka

    tonka Funster Life Member

    Joined:
    Jul 2, 2008
    Messages:
    5,325
    Likes Received:
    7,580
    Location:
    Cannock, Staffs or Benidorm, spain
    On my Autotrail there is a plug in adaptor ready for another battery. The official lead you can buy is quite thin. Also if you look at the size of the cable feeding the leisure battery to your Power supply and around the van, that is only thin...
     

    Attached Files:

    Last edited: Oct 2, 2013
  3. pappajohn

    pappajohn Funster Life Member

    Joined:
    Aug 26, 2007
    Messages:
    29,452
    Likes Received:
    16,883
    Location:
    YO11 2BD
    you are correct in they shouldnt be thin....but how thin is thin

    i would use at least 4mmsq depending how far apart they are...6mmsq would be better.
    really depends how much current you will use, thicker wire = more current
     
  4. Southampton

    Southampton Funster Life Member

    Joined:
    Dec 16, 2011
    Messages:
    511
    Likes Received:
    289
    Location:
    Hampshire
    Thanks Tonka, yes the additional plug in lead is about 2mm and very flexible, which makes me think it is thin multicore. It just doesn't look like it is man enough for the job. The cable from the power supply is also thin and maybe not quite double the size, but the core diameter is quite heavy duty. The dealer did say that it was the lead supplied by Autotrail.

    I am used to having good thick heavy duty battery leads, maybe times have changed and it is okay............thanks.
     
  5. hilldweller

    hilldweller Funster Life Member

    Joined:
    Dec 5, 2008
    Messages:
    26,421
    Likes Received:
    25,076
    Location:
    Macclesfield
    As a matter of interest what is that fuse rated at ?

    This came up a month or so ago, I'm pretty sure we all agreed it did not look fit for purpose then. Nothing changes my view today.

    I hope we are not missing the point here. Those thin wires effectively make the second battery a charger, the first one takes the brunt of the current and the second one charges via the resistance of the cables.

    Just the opposite when on charge, the first gets full volts and the second catches up when the first is full.

    It does not sound right at all.
     
  6. Southampton

    Southampton Funster Life Member

    Joined:
    Dec 16, 2011
    Messages:
    511
    Likes Received:
    289
    Location:
    Hampshire
    That fuse is 20A the same as the one on the main charging lead.
     
  7. pappajohn

    pappajohn Funster Life Member

    Joined:
    Aug 26, 2007
    Messages:
    29,452
    Likes Received:
    16,883
    Location:
    YO11 2BD
    the physics of amps, volts and Ohms havent changed though.

    more like cost saving measures by the converters....they will be using the absolute minimum diameter they can safely get away with.

    in the domestic electrics world, meter tails have increased from 6mm many years ago to 25mm today.
    electric needs have increased so the supply wires need to be able to carry that increased load.

    motorhome electric needs havent reduced, they have increased so the supply wire size also needs to increase.

    the battery interconnecting leads on my motorhome are electric welder cables, around 16mm, as are the feed wires from the batteries oo the fuse panel.
     
    • Like Like x 2
  8. Southampton

    Southampton Funster Life Member

    Joined:
    Dec 16, 2011
    Messages:
    511
    Likes Received:
    289
    Location:
    Hampshire
    The cable on the equipment side of the fuse is so thin (blow up Tonkas photo) that it is hardly fit for purpose. You hit the nail on the head......more cost saving measures.
     
    • Like Like x 1
  9. hilldweller

    hilldweller Funster Life Member

    Joined:
    Dec 5, 2008
    Messages:
    26,421
    Likes Received:
    25,076
    Location:
    Macclesfield
    Beats me, that cable does not look like 30A ( which the fuse will pass for a while ) and the connector doesn't.

    But if the rest of the wiring is also skinny what's the point in beefing that bit ?

    On the previous thread Rainbow Chaser commented that modern cable looks thinner because of thinner insulation and he's constantly replacing it because it's basically crap. Or something like that.
     
    • Like Like x 1
  10. pappajohn

    pappajohn Funster Life Member

    Joined:
    Aug 26, 2007
    Messages:
    29,452
    Likes Received:
    16,883
    Location:
    YO11 2BD
    looking at the blue and brown bits in the pic i wouldnt wire a car radio with that, never mind power a motorhome wiring system.!!!!
     
    • Like Like x 3
  11. tonka

    tonka Funster Life Member

    Joined:
    Jul 2, 2008
    Messages:
    5,325
    Likes Received:
    7,580
    Location:
    Cannock, Staffs or Benidorm, spain
    I can only quote from experience, on my old Autotrail I used the exact same cable as supplied by Sergent Electrical. Had that with 2 batteries running for 4 years.. Never any issues.
    Also have the same on my current install for the past 6 months.

    Like others I have often thought the cable must need to be thicker, the solar cable I use puts this to shame BUT if they only use the thinner stuff on the vehicle build and they are not bursting into flame (touches wood.) then it must be ok... ??
     
    • Like Like x 1
  12. Southampton

    Southampton Funster Life Member

    Joined:
    Dec 16, 2011
    Messages:
    511
    Likes Received:
    289
    Location:
    Hampshire
    I agree with all the comments, but what can you do when the manufacturers are cutting costs all over the place. At least I am now aware of a potential failure when out in it so will carry a length of decent guage cable waiting for the inevitable.......thanks guys an interesting thread.
     
  13. jonandshell

    jonandshell Funster

    Joined:
    Dec 12, 2010
    Messages:
    5,253
    Likes Received:
    7,858
    Location:
    West Norfolk
    After looking at several motorhomes with Sargent electrical systems, I personally would never own one. They are just not fit for purpose for off-hookup use. The batteries will never charge properly due to the stupidly thin cables creating massive voltage drops.
    OK for constant use on hookup, but no good for anything else in my opinion.:Sad:

    CBE and Schnaudt systems seem far better specced as regards cable sizes in my opinion.

    The best ugrade to a Sargent system is a B2B charger and a new heavy cable charging circuit in my opinion.:thumb:

    Sorry to upset you Brit van owners out there!:hardhat:
     
    • Like Like x 1
  14. hilldweller

    hilldweller Funster Life Member

    Joined:
    Dec 5, 2008
    Messages:
    26,421
    Likes Received:
    25,076
    Location:
    Macclesfield
    We've read so many times "remove the control panel, unplug it, re-plug it, now it will work for a while". Most £2 Chinese gadgets have a reset button you can poke at through a hole.

    We were wild camping on Sky and got talking to our next door neighbours. "We are going to have to leave tomorrow, the heating has failed and we can't stand the cold for medical reasons". I looked. "DING". Unplugged the Sargant control. Bingo, heat restored. She tried to give me a £20 note but the look on her face was more than enough.

    I noticed a comment on Sargent somewhere "the new ones made in Italy" were the words that caught my eye. Have they dumped Brit produced iffy ones and just import them now ?
     
  15. pappajohn

    pappajohn Funster Life Member

    Joined:
    Aug 26, 2007
    Messages:
    29,452
    Likes Received:
    16,883
    Location:
    YO11 2BD
    we use a lot of Italian made electrical components in the course of work......mainly specialised lighting and control gear.

    nothing but trouble, badly manufactured and poorly assembled....'quality control' is not in the Italian vocabulary.

    certainly wouldnt have it in my house.
     
  16. TheDogMan

    TheDogMan Funster

    Joined:
    Mar 29, 2011
    Messages:
    655
    Likes Received:
    360
    Location:
    Rugby UK
    I am with papajohn, I had a guy out last week, Northampton Motorhome Services ( after being let down by a Nuneaton company twice) I asked him about the lead thickness connecting my 2 x 220amp batteries he said they were 12mm which was the minimum he would reccomend, he had 16mm on his own Euromobile
     
    • Like Like x 1
  17. Ed Excel

    Ed Excel Funster

    Joined:
    Nov 27, 2012
    Messages:
    863
    Likes Received:
    577
    Location:
    Ribble Valley
    There is not much point in oversizing cables for battery interconnection when the load can only ever be 20A (fuse rating). 1.5 sq mm cable is capable of carrying 20A, under certain conditions it's quite happy with more. The voltage drop on a 1.5 sq mm cable, used to interconnect batteries located adjacent each other, will struggle to reach 0.25V at full load. If the batteries were not adjacent larger cable may be required.

    You should also consider, when the positive and negative cables are connected to the terminals on the same battery (battery 1). This puts more of the load on battery 1 and it also gets a higher charging voltage when the dual-battery pack is being charged. Battery 2 doesn’t work as hard because it has extra resistance to overcome in the cables that connect it to Batt 1. Battery 1 doesn’t see that resistance so it is not affected. The cable and connection resistances reduce the efficiency of Battery 2 when loading or charging. The +ve lead should be connected to Battery 1 and the -ve to Battery 2.

    Hope this helps.
     
Loading...

Share This Page