5

5tox

Active Member
Having recently bought a disco i am doing various odd jobs in preparation for MOT,
I noticed the other day that the truck has 2 batteries, battery number 2 was completely flat at only around 6v, after a long charge its still dead so i took out the wiring until i have a replacement.

Can anybody explain the wiring i have taken out, i have looked up a split charge system but none of them have looked like this?

Can anybody explain what i have, Does this setup work or has somebody fitted it wrong?
I ask because in the future i'll be fitting another battery ready for extra lights, winch etc.

 
Looks normal to me apart from the connector on the right which isn't part of the dual batt setup.

Basically earths are common.
Positives are only connected via the relay when the voltage coming from the alt is above a threshold I.e its charging.

I think that unknown connector is a bodged up jump lead setup. Other observation is that wiring on the main earth and pos won't be bug enough if you have a winch.
 
Last edited:
many thanks for the replies, the below thread shows that when the engine is running the alternator first comes to the cranking battery charging it in the process, the power then goes on to the second battery.
The way that mine was set up means that the secondary battery is connected dirsectly to the alternator when the relay is closed... will this affect the way that the cranking battery is charged (will it charge slower as its sharing the alternator?)

i apologise in advance, im quite handy with spanners and a welder but electronics are not my thing

http://www.landyzone.co.uk/lz/f38/wiring-split-charge-relay-system-61268.html
 
I can't picture how that works. The relay will only connect the batts together once the relay gets voltage from the alt. Once the batts are connected both batts will be charged (or discharged) equally as though its one larger battery, there is no first/second stuff going on. Obviously charging 1 x 70ah batt is quicker than 2 x 70ah batts (a 140ah batt in effect.)
 
If you just want simple setup with 2nd battery for accesories with engine off just get a caravan relay
 
I would check your starter battery/engine bay to see if there is another white connecter any where.
I've seen people have Anderson plugs connected to both the starter battery and the second battery as Mike said as a manual jump lead.
But if the battery is goosed it could have been a socket to plug in a mains battery charger and be able to shut the bonnet while it was connected rather than croc clips.
 
how i see it alternator kick in. power kick the relay open sending power from the alternator
to a spare battery not connected to the main set up (just 2 wires from the alternator).
the plastic socket is like a flymo one (pretty common)
nice and simple
 
Having looked at the PIC again id agree. Normally the red pos wire labeled alternator normally goes to the starter battery. In the pictured setup no single load can discharge both batteries. Useful for fridges and stuff but not ideal for winching where the dual batteries give you more oomph and longevity.

My setup has both batts connected when charging but also have dash mount button to disconnect them manually.
 
Yes charging two batts means half as quick as one.
Using alt to trigger relay stops you starting off aux battery. This is not nec an issue but the above idea of a 30amp caravan relay holding 100s of amps to a starter in Jan cranking a diesel is not good. You would need a big relay to be sure of not frying it. Hence do not use a trigger of ign etc as suggested unless your running a winch solenoid or some beefy relay for your system.
Check it has a diode on relay or you can cook the alt.
For jump starting, use jump leads :D
 
The caravan relay won't connect during starting...... Think about how it works when you really do have a caravan attached and its onboard battery fitted
 
Caravan relays are the simplest option. Most of them have two switched outputs. Due to the change in wiring standards only one is needed for the towbar, so you can use the other for charging up the second battery. The two batteries are only connected when the voltage is above a threshold, so on cranking you're just using the starting battery.
 
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