Leisure Electrics 12v (Split Charge)

Feb 5, 2013
Leisure Electrics 12v (Split Charge)
  • Leisure Electrics 12v

    You've got a van and want to make the most of it as a camper. One of the main things you will want to do is think in advance about power and how to install electrics into your campervan.
    There are a number of issues relating to electrics in a camper. If you have any plans whatsoever to sit in your campervan for an evening with the lights on, music playing then I suggest you fit a second battery.

    Installing a Second / Leisure Battery in a Campervan

    If you don't install a second battery into your campervan to run key electrical items off, then either you will at some point run your van battery down to the point where you can't start the engine in the morning; or you will constantly be living in fear of using up too much electricity and will end up reading by the light of head-torch rather than risk needing a jump start the next day.

    Van Battery Types
    There are two types of vehicle battery - starter batteries and 'second' batteries (second batteries are also known as 'leisure' batteries and 'deep cycle' batteries). Starter batteries are designed to supply large amounts of power in short bursts - specifically to start the engine; starter batteries are not designed to get regularly run down - they function best when the engine starts first time and the alternator then tops them straight back up.
    Leisure batteries on the other hand are designed to function well when you run them almost completely down time after time - this is why they are called 'deep-cycle'.
    Leisure batteries can in an emergency be used to start an engine, but they are primarily designed for extended use by lower power devices.
    Of course you do still need a way of re-charging the leisure battery, so the ideal arrangement involves a system where your van's alternator charges both batteries while you're driving, but only your leisure battery is drawn on whenever the engine isn't running.

    Installing a Leisure Battery
    Firstly, find a good place to store your second battery. First choice is in the engine compartment. Ideally you want to have the leisure battery as close as possible to the starter battery and alternator (making charging more efficient and cutting down on cable routing)
    You also need to think of safety - batteries give out hydrogen when they charge and can potentially leak acid and even blow up.
    So if you need to site the battery inside the van due to lack of space in the engine compartment, you'll need to create a boxed in area keeping the battery isolated from pretty much everything else. In particular, do NOT put the battery right next to the gas! - definitely asking for trouble!

    Battery Wiring and Split Charge Relays
    OK, the wiring for this is actually fairly straightforward, but can be a bit daunting until you get your head round it.
    Firstly, how does the charging work - well, essentially your van's alternator charges your starter battery whenever you're driving, and you want to hook your second battery up so that it gets charged as well. All that’s really needed to achieve this is a big cable running from the positive terminal of the starter battery to the positive terminal of the leisure battery, plus you obviously need to get an earthing cable and connect it between the leisure battery's negative terminal to a good (non-painted) earth bolt somewhere on the body of the van. At the simplest level, this is all the cable you need to get the alternator to charge the battery.
    Unfortunately its not quite as simple as that, because you want to protect both batteries from getting used at the wrong times. One solution to this problem is what’s called a 'Split Charge Relay'. The diagram below sums up a "split charge relay" set-up pretty well...

    The trigger wire for the relay needs to come from the dash warning light wire you are looking for the wire (normally blue) that either comes from the regulator (located behind the air filter) see diagram or from the alternator if it has a internal regulator.

    To check you have the right wire turn the ignition on so that the dash warning light is lit then pull the wire off if the light goes out you have the right wire.
    Some people will tell you to take the feed from the coil my advice is don’t as this will mean the battery’s will be connected together as soon as the ignition is switched on meaning that the starter will take power from the leisure battery.

    Now what do you need.
    You can buy a kit like this


    Or source you own.
    but it is essential to use the correct size of cable.
    You will need to know the maximum ‘amps’ each single cable might have to carry and use a cable of more that that rating
    Voltage will ‘drop’ progressively the longer the cable run, this should be taken into consideration when selecting cable size. As a general rule go one size bigger.
    For further information of relays and testing read this excellent guide.


    For cable sizes


    Now you have the spiltcharge system in place you can connect the circuits you want to run from the leisure battery.
    I recommend you use a fuse board something like shown in the kit you can mount this where you like and run a cable from the battery to one side of the fuse board then using the correct rated fuse run a cable to your light etc.
    I like to use 2 core cable and have a central earth point by the fuesboard this has several advantages.
    It makes testing easier
    you don’t have to fund a good earth at the light so if its mounted on wood it not a problem
    You don’t have mutable earth points to drill that then can go rusty.

    When running cable make sure it is well secured along it length and if it passes through a metal panel it is protected from abrasion and vibration by using a grommet.
    If in doubt find a electrician who knows vehicles or ask on hear.
S1mon, JT1 and bobbyplums like this.