Linking cab battery to leisure battery/panel when laid up?

Discussion in 'Solar Power' started by magicsurfbus, Oct 24, 2010.

  1. magicsurfbus

    magicsurfbus Funster

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    Simple query (I hope):

    I have a 85W monocrystalline solar panel on the roof, linked via charge controller to a 110Ah Elecsol carbon fibre leisure battery. It all works fine, and when laid up over winter the leisure battery remains fully charged.

    However, the standard Fiat Ducato cab battery, which has three of those £10 solar trickle chargers connected to it in parallel (when laid up) routinely goes flat in winter.

    I don't particularly want to fork out for another solar panel and charge controller.

    It seems to me that it would make sense to link the leisure battery to the cab battery in parallel via some domestic-type electrical cable when the van is parked at its outdoor storage site. That way, the charge-controlled solar panel tops up both batteries.

    Is this a sensible thing to attempt? And if so, what rating of cable should I use to remain safe? 10 Amps maybe?

    Any advice/tips most welcome.
     
  2. pappajohn

    pappajohn Funster Life Member

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    no reason why not but do fit a 10a fuse in both ends of the link wire.

    one drawback would be both batteries will be flattened if the panel gets covered in snow etc or a lack of sun for weeks on end.

    you still only have the output from one panel charging twice the battery storage though so will take twice as long to charge to the same state as one battery

    with the lowish amps from the panel a 2.5sqmm flex should do the job.
     
  3. Snowbird

    Snowbird Funster Life Member

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    Am not sugesting that this is the correct way to do it but,is it possible to run a wire from the outlet on the charge controler,you know the one with the picture of a bulb on it,direct to the engine battery?.
    I believe that this outlet is used as a dump when the leisure batteries are full,so any surplus charge would go to the engine battery.
    Hope this makes sense cos I would like to do it myself.
     
  4. pappajohn

    pappajohn Funster Life Member

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    i think thats limited to a very low ampage...probably much less than 1 amp.
    could be wrong but thats my understanding.
     
  5. Snowbird

    Snowbird Funster Life Member

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    I know of people that charge there mobile phones from this outlet,and would it realy matter if it was a low amp as long as it trickle fed the engine battery.Do you think any harm would come to anything John,I dont want to do any damage.
    Have asked this question a few times but nobody seems to know for sure what that conection is for.
     
  6. 1948

    1948 Read Only Funster

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    BRIDGING FUSE.
    Loss of battery charge due to the alarm system, vehicle clock, on board computer etc is normal over a period of time. Batteries also have an internal amount of self discharge and this gets worse with age.
    Both the vehicle and the leisure batteries have their negative pole connected to the vehicle chassis. Without this the vehicle alternator could not charge both, the leisure battery of course via the split charging relay.
    My simple method is to fit a pair of blade type fuse holders in a position that can be see every time the vehicle is entered via the driver’s door, in the foot well. One fuse holder has no wires attached, its is purely a park position for the fuse. The other fuse holder is connected one side to the positive terminal of the starter and the other side to the positive terminal of the leisure battery. This holder is clearly marked with white paint.
    When the vehicle is laid up during the winter fit the 10 amp fuse in the wired fuse holder. This enables either the solar panel (if you have one) or the on-board stabilised charger unit to top up both batteries. During the summer and all other times the fuse is moved to the un-wired “park” position.
    Should one forget to move the fuse to the “park” position and start the engine, the fuse will blow. So carry a few spares!

    Don’t forget, the bridging fuse is intended to be used as a bridge ONLY during winter lay-up so that the solar panel or when you connect your van to the mains hookup once or twice a month you can fit the bridge and top up both batteries. Otherwise place the fuse in the unconnected PARK position.



    Came across this , may or maynot fit the bill

    [​IMG]
     
  7. scotjimland

    scotjimland Funster Life Member

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  8. magicsurfbus

    magicsurfbus Funster

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    pappajohn, 1948, ScotJimLand: Thanks for the pointers there, most helpful.

    Snowbird: I've got a small solar panel on a garden shed at home wired via a charge controller to an old car battery which I use for recharging small domestic gadgets like laptops, mobile phones etc. I've tried using that spare connection on the charge controller to recharge a Halfords 20Ah Powerpack without much success, and although the correct voltage is present I'm not sure (as pappajohn says) if sufficient ampage is there.

    On some charge controllers that connection has a light bulb symbol on it, so I suspect it may be for low amp applications only. It works OK charging AA batteries and the like but that's probably the limit.
     
  9. Wildman

    Wildman Read Only Funster

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    on my charge controller the lightbulb is the connection for the load, this gets disconnected in event of low volts on the battery to prevent battery damage. any connection between the two lots of batteries should include a diode to protect and isolate each battery bank.
    Try fitting this one
    http://cgi.ebay.co.uk/MOTORHOME-SPL...ervan_Caravan_Accessories&hash=item19c07353b1
    make sure you connect the right way round.
     
  10. Snowbird

    Snowbird Funster Life Member

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    I always thought it was for the load,but the hole is not big enough to put the wires in to my load,so thats why I thought you could charge the engine battery from it.I have 2 contacts for solar panels plus 2 contacts for batteries plus the one with the bulb on it.Surely if it will power a bulb it will charge a second battery.I was told the contacts on the bulb only have power to them when the leisure batteries are full.
     
  11. Wildman

    Wildman Read Only Funster

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    I suspect the voltage will not be high enough to charge, but easy to check, will have to be well in excess of 13v
     
  12. magicsurfbus

    magicsurfbus Funster

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    Thanks for that pointer Wildman - at the risk of seeming a) a bit thick and b) overcautious regarding electricity, that set up would work just as well with the leisure battery as the main source and the cab battery as the secondary battery yes? No problem with the engine being off while it's laid up?

    What I'm driving at here is at absolute best the solar panel would be putting 7 amps into the batteries, and probably a lot less in winter, given that the panel is flat and not angled. Is that kit rigged for a certain minimum charging ampage?
     
  13. pappajohn

    pappajohn Funster Life Member

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  14. Mixter

    Mixter Read Only Funster

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    If you 'aqquired' this from the same bloke as myself - folk can take it for granted he knows his stuff! Im about to fit this myself, having had the info for long enough. :Doh:
     
  15. scotjimland

    scotjimland Funster Life Member

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    this is a cheap way of doing it, one I wouldn't recommend. if you go this way ensure you fuse the linking cable at BOTH ends .. also, if the panel stops charging there is a risk of flattening BOTH batteries

    I gave the correct solution in my first post ..
     
  16. magicsurfbus

    magicsurfbus Funster

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    ScotJimLand: Thanks for your earlier recommendation re the split charge relay and fusing arrangement. I rigged up a cab battery topping up circuit as advised and it's been a complete success.

    Before I installed it, during the first of this winter's cold spells, I found the cab battery was as dead as Disco. I managed to jump start it and drive the van around a bit to top it up.

    I installed the circuit in time for the second cold spell, and on my return to the van recently the cab battery was showing all four lights on the monitor panel (it hardly ever does that at rest) and it started first time.

    The relay I used was a Smartcom unit (£12 on eBay), mounted in a small electronic project box for protection.

    Excellent advice there sir.
     
  17. G4GMO

    G4GMO Read Only Funster

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    Breaker

    Instead of fitting a fuse I fitted a 16 amp circuit breaker which trips if I forget to turn it off. Saves the hassle of looking for a fuse each time. This is relatively easy with this Hymer since both batteries are in the same compartment.

    I'm fortunate enough to be able to keep mine on the drive and can keep the hook up connected during the cold weather.
     
  18. otis the staffy

    otis the staffy Read Only Funster

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    battery to battery

    magicsurfbus I have 85+130 giving 215watts these are fitted on tilt hinges and the feed 6* 85 amp batteries.A ten amp cable connects the liesure batteries to the drive battery through a 12 volt relay when we originaly fitted it we installed an on\off switch in the glove dropdown but on 2 occasions I forgot to switch it on and flattened drive battery so now it stops on all the time.System now been in use 6 years no problems allows for radio,alarm system,navigator and 12 volt inverter for the lap top, due to the fact that as fast as i use the power from the drive battery it is pulling the power fron liesure batteries which in turn allows the solar\genny to top everything back up.Hope it helps.Stay Safe:thumb:
     
  19. wivvy's dad

    wivvy's dad Read Only Funster

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    Holy resurrected threads Batman.........................:Eeek:
     
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