[kd883]

Hi guys,

I recently made a fairly crude but nonetheless useful dual battery system for my Sierra for about 100 bucks.

Bits I used:

Given that the starting battery I had was ok (Repco will test this for free if you ask nicely), I bought another one for starting the car (battery 1) and used the existing battery as the auxiliary (battery 2). This cost $65.

I then picked up some bits of scrap metal from the council clean up (when people throw all their rubbish out on the street and it sits there for about 2 weeks before the trucks come to collect it). I used one piece of angle and 2 pieces of flat bar.

I then bought the following items from Repco:







You will notice that I also used a rectangular bracket to hang the charcoal canister off and sit the battery on. If you can't find something like this, Repco sell a plastic one like this (see below) or you can get a metal one from Supercheap for about $20.



For the wiring, I used an old set of jumper leads, but you can also get these from The Reject Shop for $6.

The nuts, bolts and washers I had in the shed, so I didn't factor these into the cost price. I can't imagine that buying these would blow the budget if you had to though.

I also bought a packet of eyelets for the ends of the wiring, which were about $3 from Jaycar.

All up, I spent $105.

What I did

1) Installed new battery on drivers' side.

2) Removed charcoal canister.

3) Cut a piece of angle, painted the fresh steel to prevent rust, and fitted it in the place of the charcoal canister, using the existing bolts and washers.



4) Dummied up the fit of the battery bracket. Had to massage the wheel arch a bit to get it to sit flush at the front.

5) Drilled the holes for the mounting bolts, the battery retainer bolts, and the bolts to hang the charcoal canister off the side.





6) Bolted the bracket in and the charcoal canister on the side.

7) Cut that bit of scrap flat bar to make a base for the battery and cut the notches out for the bolt heads.



8. Trimmed the battery retainer bolts to clear the bonnet. (Please ignore the piece of flat bar in the middle of the bracket).



9) Fitted auxiliary battery (battery 2). Note that the plastic retainer that came in that kit from Repco is pretty soft - I ended up replacing it with a piece of flat bar but the kit is still worth the 7 bucks for the hooked bolts, washers and wingnuts.



10) Cut a hole in the dash and dummied up the fitting of the switch using some thin flat bar and screws.

11) Ran a wire from the positive terminal on battery 1, through an existing rubber grommet in the firewall, through to the switch.

12) Ran another wire from the switch to the positive terminal on battery 2, thus linking the charging system.



13) Fitted switch to dash.



14) Ran a wire from the negative terminal on battery 2 to an existing earth point on the firewall, completing the circuit.



I then went one step further and rewired my radio and cigarette lighter to run from battery 2 entirely. This means that now when I pull up at camp, I can can isolate battery 2 using the big red switch, run my radio and charge electronic item from the cigarette lighter, and then still have battery 1 for starting the car in the morning. I also bought a cheap little inverter from K-mart to run a small fluro, so now I have a nice, bright light to work with at camp too.



I hope you find this thread useful. Thank you for reading.

KD.

[jdk81]

Just a heads up.
Put that switch on the negative/earth side, so if theres a short it wont matter too much.
Its dangerous as it is

[pezz]

I'd hate to wear that isolator in my knee during a crash...

[Davros-1]

I like what you have done, basically it gives you peace of mind for not much outlay - or ungentlemanly effort in summertime.

I too don't like the switch location - my choice is in the glove box 'cos it's out of reach of the compulsive fiddlers, and that's where the bonnet release is anyway so it's accessed often enough.... Isolating the negative is the better option as well in case you get chafing of the interconnects - failure of an earth strap is way less exciting than a positive feed, trust me, I've tried it.

Remember that the rating of low voltage wire is it's failure point, so if you expect to feed 40 plus amps into your inverter at full output you need at least twice that rating in the wiring - for minimal voltage drop I would specify three times the total potential maximum current draw in any low voltage system.

And if you are going to run two batteries, make sure they are of the same type. That is, don't mix deep cycle, AGM, GEL, Flooded lead acid etc.

Can't work, as the differing internal structures, resitive loads etc. mean one at least of your batteries will be overcharging/undercharging/cooking.

If you are going to use starting batteries remember that the alternator at best will only bring your batteries up to around 75% charge. There are several reasons why but the main point is that your starting battery is only designed to do that, start the engine which then runs all the electrics from the alternator. If you draw a starting battery down below 50% you will damage it, do it real hard and often and the battery is quickly reduced to a useless state.

So to be safe you really only have 25% of the total rated capacity of your second battery available at most until you start to damage it. Makes LED lighting all the more attractive!

My son and I are doing a similar thing to a F10a - but we have a couple of relays and plenty wiring from other twin battery setups (ex Landcruiser stuff, way big enough I think!) to use rather than the manual switch.

Thank you for the article

Edit - the setup is exactly as claimed, a basic dual battery system. Any critisism absiolutely should be taken as positive (groan...). Manual switches are so 1970's Voltage sensative relays are the only thing that should ever be connencted if there is ever any chance of the battery being separated from the alternator - which is not the case here. If wiring is well routed and correctly isolated there is no reason the setup as shown will not give indefinite life, and if the battery is not isolated, oh well - still got twice the original capacity or more. There is the advantage if on full veiw that the switch is less likely to be forgotten - all the VSR does in a 'proper'dual battery setup such as Redarc etc. is respond to an input from the ignition 'on ' feed to connect the second battery to the alterator. If you leave the ignition on many VSR systems will still flatten both batteries, only the more sophisticated ones will separate the batteries if the engine is not running (oil pressure switch feed, alternator charge output etc.)

A battery is a group of cells connected in series and/or parallel to give you the required capacity and voltage - your 12v car battery is 6 x 2v cells in a single case, you have two fitted (in this case in parallel) therefore you most definitely have a dual battery setup. Manual switching is irrelevant. All the alternator sees is a single larger capacity battery in the circuit. It really is that simple.

Of course any simple system can be improved, but for this budget I think the effort is wonderfully effective, and also hope more articles come from this poster.

[pezz]

Just on another note, if you forget to remove your isolator whilst at camp you will drain both batteries...
Might be woth the spend for a automatic isolation system like a red arc voltage smart relay.. just takes the human error out of the system

Two flat batteries would be crappy

[Gwagensteve]

Truth there.

All due respect, but that's not a dual battery "system". It's two batteries and a switch. There's lots of room for user error there.

Steve.

[shep]

You payed $20 for the isolating switch, same company sells VSR solenoids for $45. If you replace the switch with a solenoid it will be a good setup.

Take everyone's comments as constructive and keep posting when ya make stuff, to many people here just web wheel and never actually do anything .

[oohsam]

shep wrote:

You payed $20 for the isolating switch, same company sells VSR solenoids for $45. If you replace the switch with a solenoid it will be a good setup.

Take everyone's comments as constructive and keep posting when ya make stuff, to many people here just web wheel and never actually do anything .

Spot on shep. Lots of haters.

Good first effort man. Keep at it.

[pezz]

I wouldnt say haters.
Just trying to save a bloke having a isolator hanging out of his knee cap
Or two flat batteries in the middle of no where..

Isnt that what these forums are for? Helping each other out

[jdk81]

And trying to help avoid a carBQ