cheap and simple dual battery set-up

[zuknewbie]

Have been lurking around for awhile and have finally started to set-up the xterra for some light-duty overlanding. I want to install a second battery for the sole purpose of running my ARB fridge, but dont want to spend lots of money.

My idea,
starting battery pos. hooked to 100amp fuse to a manual disconnect switch to pos. of auxillary battery, auxillary battery neg. to chassis ground

The plan would be to have the auxillary battery hooked up to the starting battery only when the truck is running, hence the switch. When i shut the truck off i would turn the switch off and after starting the truck flip the switch on. The set-up is only gonna get used for 1 two week trip each year and for dry camping a couple weekends. Any concerns our ideas are greatly appreciated as wiring is not one of my strong suits.

 

[dwh]

A) You'll forget to turn it off at some point, sure as shootin'.
B) It's not cheaper than a split-charge relay (which does the switching automatically), and except for the two extra wires from the solenoid to an ignition circuit, and to a negative, not any simpler either.

The split charge relay is just one wire from Battery A + to one side of the solenoid, one wire from Battery B + to the other side of the solenoid, one wire from an ignition circuit to the solenoid to energize it while the key is on, and one wire from the solenoid to negative (frame "ground" or whatever).

http://www.amazon.com/SOLENOID-GOLF..._2?s=automotive&ie=UTF8&qid=1311615797&sr=1-2


If both batteries are under the hood, and only connect to the solenoid or switch, then you don't need to fuse their main positive wires. If the aux battery is some distance away, then you should fuse the wire to it.

You do of course, need to fuse whatever wires you tap off the aux battery to feed loads - such as the fridge.

 

[CoastalDefender]

I'm a dolt. Is it REALLY that easy? What happens to the main battery when the house battery is depleted while connected to the relay?

What happens with that relay when you deplete your main and have to jump off the house battery?

 

[Deleted member 9101]

I'm a dolt. Is it REALLY that easy? What happens to the main battery when the house battery is depleted while connected to the relay?

What happens with that relay when you deplete your main and have to jump off the house battery?

If the main battery lacks the voltage to throw the solenoid when you turn the key, you just unbolt the lug going to the 2nd battery and place it on the one going to the main battery. Basically bypassing the solenoid.

 

[CoastalDefender]

If the main battery lacks the voltage to throw the solenoid when you turn the key, you just unbolt the lug going to the 2nd battery and place it on the one going to the main battery. Basically bypassing the solenoid.

So put the solenoid in a place that's easy to access?

IDK, I'm still not convinced the solenoid is as a controllable option for myself as a Blue Sea m-series battery switch P/N 6007.

I just got my 31M battery today, and am sourcing the cables from a local shop, so this is of keen interest to me at the moment.

Now, welding cable, battery cable, which is preferable and why? I am leaning towards welding cable due to the flex and ease of routing...

 

[Deleted member 9101]

I would put it in a easily accessible place, but thats just me. I use one to charge my trailer battery, cost me all of 12 bucks.. works perfectly. As for the cable, I used stuff I had lying around from. I know people use the welding wire with no problems, just get it the right size for your application (or if you are like me, the biggest that you can make work)

 

[dwh]

I'm a dolt. Is it REALLY that easy? What happens to the main battery when the house battery is depleted while connected to the relay?

Nothing happens to the engine battery. That's the point; When the ignition is off, the batteries are isolated.

This is also why you connect it to an ignition hot and not an accessory hot - you can park and listen to the radio off the engine battery like normal, but still keep the batteries isolated until you start the engine.

What happens with that relay when you deplete your main and have to jump off the house battery?

It's happened to me a couple of times - left the headlights on all night.

Turned off the headlights and waited a couple minutes and the engine battery came up enough to activate the solenoid. The solenoid only draws about 1 amp.

Once though, the battery was too dead to energize it, so I just busted out the jumper cables (both batteries are under the hood).

You could if you wanted to, add a wire off the aux battery to a switch to the solenoid, so that if you ever needed to, you could flip that switch and energize the solenoid off the aux.

Another option, would be to have a small wire with alligator clips on it, and clip it to the large solenoid terminal from the aux battery, and to the small terminal from the ignition - that would energize the solenoid as well.

Or, just a momentary push button switch screwed down right next to it. Once it's energized, there is power coming through it from the house battery side to the engine battery side, so it stays energized. [EDIT: Provided the key is on, of course.]


Or, do as Jnich suggested.

Or, just clip both ends of the jumper cable positive to the two large terminals on the solenoid.

 

[Deleted member 9101]

Or just swap the batteries....lol

 

[dwh]

So put the solenoid in a place that's easy to access?

IDK, I'm still not convinced the solenoid is as a controllable option for myself as a Blue Sea m-series battery switch P/N 6007.

Either one is a switch. One you can forget to switch it and cause yourself problems, the other is automatic.

I just got my 31M battery today, and am sourcing the cables from a local shop, so this is of keen interest to me at the moment.

Now, welding cable, battery cable, which is preferable and why? I am leaning towards welding cable due to the flex and ease of routing...

Welding cable is preferable for a few reasons: More flexible, tough high-temp sheathing, finer strands. It's also usually available in larger gauges than battery cable if you need serious beef - like for a 3000w inverter.

A welding supply shop can cut the cable to length from a spool and crimp the lugs on as well.

 

[dwh]

Or just swap the batteries....lol

Or fire up the generator and battery charger.

 

[Deleted member 9101]

or fire up the generator and battery charger. :d

winning!!!!!

 

[dwh]

winning!!!!!

Heh. But really, it's no joke. I *am* sometimes an idio...uh...absent minded, and have left the headlights on AND ran the aux battery down. Fortunately, I do have a generator and battery charger to save me from my own stupidity.

But the charger is hard-wired to the aux battery, so I had to bust out the jumper cables to charge the engine battery.

And my jumper cables are 1/0 - they weigh a bloody ton.

Oh, woe is me!

 

[wrcsixeight]

I would not want the starter amps flowing through the solenoid if the main engine battery was too low to do the job. The one linked to was 90 amps continuous, 150 amps surge. The starter can and will pull more than that and might weld the contacts in the solenoid together resulting in no battery isolation which might not be realized until you are really up dodo creek in a barbed wire canoe without a paddle.

If the engine battery were to go dead, I would jumper it by moving the Aux battery cable to the same lug on the solenoid as the starter battery rather than by powering the solenoid with the good battery.

 

[dwh]

I've done it a couple of times - started the 460 without any issues and still works fine. But yea, it could be an issue.

 

[Deleted member 9101]

Heh. But really, it's no joke. I *am* sometimes an idio...uh...absent minded, and have left the headlights on AND ran the aux battery down. Fortunately, I do have a generator and battery charger to save me from my own stupidity.

But the charger is hard-wired to the aux battery, so I had to bust out the jumper cables to charge the engine battery.

And my jumper cables are 1/0 - they weigh a bloody ton.

Oh, woe is me!

I caught one of those "jump boxes" on sale for 49.99 at auto zone a few months back. thats my easy way of dealing with it...lol