Manual Dual Battery set-up

[D40Craig]

Okay, I am thinking of installing a MANUAL dual battery set-up in the D40. The battery will live under the tray. All I was thinking about doing was to run a heavy (and in conduit) positive cable from the main battery to the second battery with a large fuse, maybe 100amp, and a heavy earth to the chassis. I was planning to install an isolation key (one of those big red ones) in-line and close to the second battery in the positive cable so it is easy to access. All I would do is disconnect the second battery via the red key when camping and running the fridge and lights and then reconnect when the car has started and charge the second battery.
Does anyone see any problems in doing this?

 

[Old.Tony]

No problems unless you forget to break the circuit when camping! You need a fuse on the aux battery side too - it's a power source capable of causing damage while driving.

Be aware that your alternator may not provide a full charge to your starter battery, and because the aux is going to be on a long cable there'll be a lower voltage charging it, so it will have a slightly lower state-of-charge.

 

[D40Craig]

Okay, thanks Tony. I would most likely start the car and then switch back over. I realise it will take longer to charge the second battery as the alt will have to charge both at once.
And a good idea, a fuse at both ends?

 

[bods]

Dunno why you'd risk running a setup like that when you can get a basic solenoid isolator setup for less than a hundred bucks, which will do it automatically.....


In saying that, there's nothing wrong with doing it the way you want, just make sure you put fuses at both ends as mentioned above...

 

[happy john]

I used that setup for years in 3 rigs never had a problem i used 12mm welding cable if for some reason the main battery went flat you could start from the aux i only just fitted a redarc to the 22 last year after 25 years on the road.

 

[D40Craig]

Thanks Happy John. The reason for fitting such a basic system is for sheer simplicity in the bush. Not a lot can go wrong, and if it does it would be easy to trace.

 

[happy john]

My mother had a patrol she went through 2 tjm isolators the 2nd time it went on the canning i got a manual switch and whacked it in never had a issue again i found it would recharge quicker than the relay setup as well.

 

[Old.Tony]

Okay, thanks Tony. I would most likely start the car and then switch back over. I realise it will take longer to charge the second battery as the alt will have to charge both at once.
And a good idea, a fuse at both ends?

If I was to put my advice into a generic rule it'd go like this:

If you are running a power cable from a power source, put a fuse in it first in case the cable is damaged.

A cable attached to the battery in the tub (whether the switch is on or off, it's possible for it to be 'on' so it counts) qualifies. If you snag a stick the wrong way and the inner conductor is pushed hard against the chassis, your front fuse will blow and the aux battery will be the one that starts the fire.

It's just a safety thing. Even a 100A fuse will blow in a direct short, but I wouldn't try starting the car through that. Our engines draw over 500A to crank over. You might consider a means of temporarily bypassing the fuses in case of emergency.

 

[Malicious]

An old rule from my boss when I was an apprentice , put a fuse within 12" of any battery or feel my foot up ya arse.

 

[happy john]

I should of put more info in re starting from the rear i had to do it twice back then in 95 i was at fraser on the most northern point the door was left open and the light drained the main back then i had fuses not breakers i bypassed both fuses with jumper leads 12mm welding cable had a small voltage drop over the 4 mtrs to the tub and the rear battery fired the old girl with ease d21 td27t that was.I can do the same with my present farm truck in an emergency due to the heavy wiring it will carry the load well.