Fitting 2nd battery - what does a split charge unit actually do?

I'm planning to fit a 2nd battery (a "deep cycle" one) to power fridge, lights etc while camping, but maybe to use with a winch when I get one.

The question is what to do about wiring. I'm thinking about wiring the 2nd battery in parallel with the main one with a switch on the positive lead to let me
- connect the 2 batteries together for charging
- disconnect the 2nd battery from the main one and connect it to a set of sockets to let it power the accessories without the possibility of draining the main battery
Does that sound sensible to you?

Other threads say "get a split charge unit" but what does it actually do? Does it stop the main battery from being drained while letting the 2nd battery get charged?

cheers,
Rod

fit a split charge relay

RodB said:

I'm thinking about wiring the 2nd battery in parallel with the main one with a switch on the positive lead

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Not unless you want to screw up both batteries.
A split charge does exactly that. Only connects both batteries when the alternator is charging - and disconnects in any other circumstances. so that one battery cannot drain the other.

according to basic electronic theorey, if you parralel two identical batt's together, each batt will provide half the required amps and last theoretically twice as long,

the problem will be when it comes to starting your wagon in the morning, as both batts will be equally drained and if you manage to start your landy the alternator will die trying to charge both from near empty (after cranking) so in order to save your batt's and alternator fit a split charge,

there are many options including plans for Home made versions on the internet.
one envolves a relay that is switched on when the alternator is charging, but my opinion is 'buy right buy once'

The relay is used to separate different batteries so as their different internal voltages will not drain each other when the car is off.

On a not-unrelated note (and 'scuse the thread hijack), how long would it take to charge a deep cycle leisure battery from near flat?

I have no mains power in my lock-up, but have used deep cycle batteries and an inverter with some success. I used two batteries - one on charge at home, one in the lock-up, but got fed up with carting them around (live in a flat). It occurs to me that something could be done using the Landy, either fitting the to-be-charged battery into the motor, or possibly adding an inverter and taking the power straight from the Landy. However, I have no idea how long it takes to charge a flat battery (I envisage the charging being done as part of the normal running around - not planning to have the Landy sitting idling like some big generator).

it is all proportional to the current supplied to it?

i tried 3 different split charge systems before i settled with the tmaxx one..it works well and has the facility to link both batterys when ya need the bit of extra power when winching..only costs around £75 but it does what it says on the tin

wiltshire landyman said:

i tried 3 different split charge systems before i settled with the tmaxx one..it works well and has the facility to link both batterys when ya need the bit of extra power when winching..only costs around £75 but it does what it says on the tin

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have you tried the x-eng one??

You can make a cheap spilt charge relay from a old glow plug relay.
I used a ldv 400 relay.
Run a positive from the battery + to relay, same as glow plugs are set up but the other end goes onto the other battery.
And use the relay activation wires to turn the relay on when the alternator kicks in.
That way the 2nd battery does not get drained when vehicle is not running.
Similar to a split charge relay but cheaper and a bit pikey

I'd be careful charging deep cycle battery's from a car alternator as deep cycle battery's require different sort of charge that an alternator provides.
That is the case for leisure battery's.
You can get intelligent chargers for your battery bank that convert the alternator current into a usable intelligent charger.
X-ALT - Alternator Charge Controller & Smart Regulator

08mckerp said:

have you tried the x-eng one??

Click to expand...

yep it wasnt as gd,its basically just a small relay about the size of a main beam relay,the wiring that comes with it aint up to the job imo..

There is a really simple way of doing this, boats have solved this problem for years.

Buy a battery master switch, it will switch on an off any of the two batteries. The switch 'makes before breaks' so there is no danger of having no battery connected whilst the alternator is going.

Simply, switch on one battery on one day, the next day, switch to the other. You can if you need switch both batteries together. Or use one at a time.

It isn't high tech but it will never fail and is really easy to install.

Thanks guys.
Some good explanations of what the split charge unit actually does.
I've ordered one.

cheers,
Rod

Got a master switch then a split charge system.
It's a cheapo one from Maplin and I might change it to another one later though.