hello all i wont to fit a second battery (in the back) to feed my cooler when away from freelander so
it dose not run main battery down.
going to fit a rely so with ign off no power will taken from main battery just the second one but with the
ign on (engine running) it with open the rely and feed the battery.
as i have a heavy power supply in the back it would be easier to mount the rely in the back but i need a trigger feed is there one in the back (wiper feed or something else that would trip a relay) if not should i run another wires from my fuse-box to the relay.
im going to us a small car lead acid battery as its easier to charge .
thanks in advance
james

Going to have to assume most of your points - as your grammar and spelling are atrocious (spell check is standard on all browsers now, so no excuses on that front)

For the battery, if you're going to allow it to mostly discharge, then get yourself a leisure battery. It'll cost a little bit more than a car battery, but is designed to be more fully discharged than a car battery is, and will survive the abuse much longer.

Keep the relay itself as close to the power supply as possible - the shorter the cable run, the better. So I would agree, keep the relay in the back, as close to the second battery as possible, along with a suitably rated fuse for the capacity of the second battery. For the switched feed, any ignition live will do, so the lighter socket may be the easiest, and closest, option.


And lastly, don't forget to securely strap down the battery. A large lump of mostly lead, in a crash, will make short work of smushing your brains into a pulp if you decide to get in its way.... A couple of bolts through an old ratchet strap works well enough, and fitting the battery inside a plastic toolbox can help stem the flow of acid if you roll over. All things worth considering tbh.

Forget running a trigger wire and fit a voltage sensing relay.

I have this Smartcom one....
http://www.ebay.co.uk/itm/MOTOR-HOM...-12V-30-AMP-/371368809769?hash=item56774e5529
which works nicely.
Saves ****ing about running another wire.


Fit a fuse close by your original battery on your feed through to the back and fit another fuse close to the second battery so that any damage to the lead will not cause either battery to short out.
For the feed wire, you are not drawing massive current through it.....well, it certainly shouldnt be - it must not be connected when you are cranking the engine, hence why a voltage sensing relay is a better bet - it will not connect the batteries until voltage is stable at 14v. A standard relay might connect as soon as you turn the key unless the trigger wire is disabled during cranking - this would risk drawing starting current of a few hundred amps through from your second battery.

DD is right - a leisure battery would be a better bet. I fitted a normal battery as I had one lying spare and it has held up ok so far - I will replace it with a proper deep cycle one if/when it dies.

thank you
dave21478 for the ebay link.
do you not need a charge controller for a leisure battery.
j

dave21478 said:

it must not be connected when you are cranking the engine

Click to expand...

The lighter socket is "accessory" live - so switches off when cranking

+1 on VSR. Had one in my old van keeping the rear battery charged. No need for a separate charger - the alternator is enough.

But I would still take an ignition feed to the rear. I've not got a 2nd battery in mine but I've fitted a 12 way fuse board (Ripca), 6 are permanent live and 6 are ignition live fed through another relay (the ignition signal closes a high current relay which is connected to the battery). That way I've got some automatic control over what's live at any time.