Dual Voltage/Second battery

[Mikes]

Hi, my name is Mike and I am new to this Forum. I have a 1994 Discovery TDi, and I want to fit a dual volatge setup to run camping accessories. Can any one point me in the right direction in terms of 'how to', wiring in etc and what bits I should use? I planned to use a leisure battery, and I believe it is possible to trickle charge it. I also have a second heavy duty battery that I would like to use as an auxilliary supply. Advice much appreciated.

[s.stirley]

What you say 'dual voltage' what's the 2nd one you're referring to ? Obviously the vehicle is 12 volts DC negative earth, are you looking to add mains then ? or do you want a dual battery 12v setup ? cheers

[Mikes]

Hi, thanks for replying, I only want a dual 12Volt setup for camping accessaries; lights, cooler ect. I believe the disco has wiring for auxilliary attachments. I need to extend the wiring into my tent which slips over the back of the disco.

Thanks again, help very much appreciated.

[s.stirley]

Sounds like you want caravan type wiring, for a 12S external socket but with a backup battery wired to the external feed with a trickle charge setup. Basic way to do that is to wire it via a relay to the main battery and switch the relay when the engine is started (usually the alternator has a 'field' output for this purpose). The wiring shouldn't be that complex, siting the second battery is the trick !

[BrendanB]

G'day,

We get a lot of guff in the 4wd magazines over here (Australia) re the correct way to set up dual batteries - and they are generally quite complex. There are even quite a few specially designed dual battery wiring kits that are meant to look after a 2nd battery in some optimal fashion.

However, I don't get it. I figure that the alternator and regulator ensure that charging does not exceed some set voltage, so I don't see the big deal in setting up a parallel 2nd battery using a fairly simple switching set-up. I have fitted a 2nd battery in this way.

The disco comes with the 2nd battery compartment, so space is not an issue. I chose a 'marine' battery, which is apparently partway between a deep cycle battery and a normal starting battery. In theory, deep cycle is better for camping accessories, but cannot deliver as high a starting current as a conventional battery. In my case I still want to be able to start the vehicle off the 2nd battery (in an emergency) as well as use it for camping accessories - hence the choice.

My wiring setup is fairly simple. I have a wire from the main battery to the 2nd, with a solenoid along the way. The solenoid is set up to connect the 2 batteries once the ignition is on, so that the 2 batteries are kept totally isolated when the vehicle is switched off. This way camping lights, etc do not drain the main battery. I have a separate accessories plug inside the vehicle that is wired to the 2nd battery. It is all fairly agricultural, but it is effective, and I haven't noticed any problems with reduced battery life on the 2nd battery - my setup is 2-3 years old now.

Cheers,

Brendan

[kevinrbeech]

Split charging kits can be bought on auction sites, at Maplins and at various other outlets. I put a second battery in my Discovery 1 last year and have had no problems to date. The important part is that the second battery should disconnect from the main system when the engine is not running, the reasons are;
1) If you discharge both batteries overnight you may not be able to start the car in the morning.
2) When starting the engine the current drawn through the battery leads is far higher than the rating of the leads required to connect the batteries for the purpose that you are using them for, in other words if they are thin wire they will melt.

The best/cheapest way to achieve what you want, at the battery end at least, is to site a second battery on the opposite side to the original. Wire the second battery to the first in parallel (red to red, black to earth, the vehicle) but putting a relay in the red cable. This relay should be wired, on the control side, to earth and to the alternator warning light on the dash. Wiring in this way will achieve the switching that you require. You can then make your connections to the battery for your lights, fridges etc. By the way a couple of well placed fuses would be a good idea.
This is only intended as an overview, if you do a search on the Internet for "Split Charging" you should find several results, specifically from the campervan sites.
Notes.
It is said that the batteries should be of the same rating for this set up.
Deep cycle batteries can be completely discharged without doing damage, unlike ordinary car batteries.
There are clever systems on the market which divert more of the charge to the battery that needs the most.
I paid about £20 for the wire, relay, battery terminal clamps etc.
Hope this helps.
Kevin

[Mikes]

Thank you all very much! I think I have got the general idea of 'how to'. Most of the acessories will be outside the Disco and located in the Caranex tent, accept for an interior light, so I suppose I could rig up a cravan s type connection. I have two spare Batteries. A leisure type 80 and a heavy duty type L95. I thought it would be resourcefull to use both. The latter as a backup for starting the Disco (it appears to have a drain on the main battery which I cannot trace) and the former to run 12 volt accessories. To use the leisure battery outside the disco I may have to rig up somthing movable/mobile.

Once again, thanks for your help.
Mikes