Thread: duel batteries

have a look at this thread http://www.aulro.com/afvb/verandah/6...ttery-kit.html Tim aka drivesafe got everything you need

Originally Posted by shad

has anyone got some wiring diagrams for instaling duel batterieshave 110 defender

You need them to work together, not fight!

From what I can remember, as long as both batteries are wired up Positive to Positive and Negative to Negative and you have a good strong alternator, both batteries will fully charge as one.

If you want to have both charge up but one drain from one, use a very large diode in series to allow the current to pass from the alternator side to both batteries but stop the current from returning on the same cable.

Cheers,
Shirl.....

Hi Shirl, diode type isolators have a major drawback, which is exacerbated in a Defender, because of the additional length of cable run between the Defender’s alternator and the Battery Box, under the seat.

Diodes cause a 0.7 volt drop which means the batteries will never be fully charged and add the voltage drop that the long cable run causes, just makes the problem worse.

If you want a KISS solution wire the second battery through a solonoid which is switched by the ignition or similar. In this case you have to use HD cable as the second battery will share starting load. You can use a circuit breaker and light wire but then its not so simple .

Also you should place a fuse in the feeder line for the solonoid. A friend had his fail in a way which dragged high current through his trigger wire and burned out his entire under bonnet loom.
I used this system successfully for 15 years .
Regards Philip A

Originally Posted by PhilipA

If you want a KISS solution wire the second battery through a solonoid which is switched by the ignition or similar.

The main reason for using something like the SC40 dual battery isolator is because it is simple to install, I might add, a lot simpler than trying to wire up a solenoid to the ignition.

The other point is that like the diode set up, there is a potential major draw back with this type of set up.

Should either battery fail, in most cases, you don’t find out it’s failed until the other battery fails and then you have no back up at all. Back to the jumper leads.

Im with Tim on this 100%.

I run Pirahna systems in mine due to.....they were there when I bought it phylosophy but most proper types of battery isolators whether it be an SC40 from Tim, a pirahna system or a redarc there are plenty of good reasons for going to these systems.

1. The first and most important in my books is that the second battery doesnt start to charge until the start battery is fully charged after start up.

2. The batteries can be dis-similar type/size so you can run a very large high CCA battery for your starter and a small aux to run lighting or what not or a normal start bat and a deep cycle aux for fridges etc.

You cant do this with a Soloniod or diode as the bigger battery will draw down the smaller all the time which will kill the smaller battery and in most cases then the larger battery wont fully charge as the smaller battery is drawing all the current the alternator is putting out to try to stay charged until both bats crap them selves.

I think Ive got that right, that my unbderstanding anyway, Tim will correct me if Im wrong.

3. They are simple to fit, most of them come with writing on the cables what to hook them up to and normally just need an ignition feed and an earth and then 2 large battery feed cables for pos on both bats.

You can get systems with volt guages, third battery feeds, dual start, jump start and it goes on and on the possabilities with these systems, it just depends on how much you want to spend.

Ive also just recently fitted up a second bat to a mates truck to run Aux lighting in the back and he just picked it up from supercheap.

I recon it will be good for his set up but not so good for 4wding as the box wasnt sealed up all that well but was only $35 + the $75 I charged to fit it so was probably cheaper than a soloniod and much better than just a diode.

I have the Redarc and (when it works) it seems to connect and charge the 2nd battery when the higher charging voltage from the alternator is evident, rather than charging the first battery and after that is done then connecting the 2nd for charging. I'm not sure if a battery can take the full output of the alternator can it? If not then I wouldn't have thought that simultaneous charging would be an issue. This said, I'm not a 12v guru.