Vehicle & Technical > Discovery

Advise needed wiring twin batteries in parrallel!

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petergalileo:
it doesn't matter if you connect something to the positive on battery A or the positive on battery B or in between.  You are effectively only increasing the size of the battery.  Its like sticking all the internal parts of the batteries into a bigger box.

I think some are confused by what they do on some lorries with 2 12 volt batteries connected in series.  In that system you can take a 12 volt feed and a 24 volt feed.

On a parallel system it doesnt make any differnce at all where you connect your accessories you will only ever get 12 volts.

I will say it again though, this only works if both batteries are both exactly the same ! If one battery is a higher capacity or one is 5 years old and one is new this will not be an good.  you will only succeed in knackering one or both batteries as the better one of the two will try and overcharge the smaller (or older) battery.

If you have 2 different batteries then you need some sort of split charge system.

Bulli:
I have a similar set up to Colin. It makes it easier to connect some things to 1 battery and some to the other. Makes for a tidy install as you dont have 10 wires coming off 1 battery. If you are running winch cables through the front of the disco they soon take up a lot of space, the 2 batteries make it a little easier i think.

colintandy:
:D at the moment i have every think wired to main battery the only thing i would wire to the second battery is going to be comms equipment and very delecate laptop ect..... evry think then has the added bennefit of running direct power from the 100amp alternator /winch /lights starter ect..but like tim says it is just one big battery now and have kept the link between the batt1 and winch isolator as short as poss to prevent any loss in power to the winch ...but im also toying with the idear of dedicatting a 24volt system just for the winch but i think its going to be overkill myself as the winch i got is powerfull enough and has not let me down yet !

Slimer:

--- Quote from: "petergalileo" ---I will say it again though, this only works if both batteries are both exactly the same ! If one battery is a higher capacity or one is 5 years old and one is new this will not be an good.  you will only succeed in knackering one or both batteries as the better one of the two will try and overcharge the smaller (or older) battery.
--- End quote ---


Asked a mate of mine about this, he used to be an auto sparks (now does far more high-tech stuff) and generally knows what he's talking about, this is his respnse:

"complete b******s, as long as the interconnecting cables are capable of the full CCA of the largest battery, no difference at all. Both batteries will balance out the charge levels, higher capacity batteries give up charge more 'easily' than lower capacity ones, so each battery will always have the same %age of charge, i.e. one battery will not empty before the other. the only thing to watch with any second / third battery installation is the recovery rate. If the alternator is not sufficiently rated, it may well overheat the regulator, rectifier, rotor, stator or all four attempting a prolonged high current recharge. In cases where deep discharge is expected a timed relay is sometimes fitted to allow 'pulse charge' on auxilary batteries to prevent this. Vehicle alternators are designed for 20% recharge, 80% direct consumption (vehicle running, acessories etc.) at revs in excess of tickover, most will only function at full output at approx 2500rpm or above"

Don't shoot the messenger.....

colintandy:
:D like i said dude i havent had any problems with my set up and i was given the advice and tech expertise by a friend who does know what he is talking about been compertion driving and winch extreem events for about 10 years now and for your mate to say its bolxxxx is very arrogant is he saying that i got it all wrong then whats his advice then dude cos it works well for me and my truck aint let me down yet dude but then i only take advice from people who do know :D

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