Correct wiring for a Redarc BCDC 1240

Good advice John.
You have it covered very well.

Brad,
Perhaps the only thing to add to John's comment is the battery bank in the tub should be of AGM style and be as big as you need to run your high drain devices such as fridge, etc.

The battery in the engine bay is better off being of the standard wet cell deep cycle variety as they can withstand heat better and are much cheaper. But what would you be running off an auxiliary under the bonnet?

Now as has been mentioned, heat is a major enemy of all batteries and they are better off out from under the bonnet.

If you are running a flat tray, the best place is under it...if you have a style side it gets harder especially if it is a dual cab.

If you want to run two batteries and you can mount them close together...by all means charge & use them in paralell......but they need to be identical batteries..same size, type, brand, age and preferably from the same batch.

when you wire them run the incomming positive to one battery the incomming negative to the other and then paralell the positives and negatives with the same length and size link cables.....this has been proven to improve the evenness of the charging and loading over other wiring options.

If you cant do that don't get all bent out of shape.

I do have some questions over the sufficiency of 40 amps charging over 200 AH of batteries...if you run batteries with limited maximum initial charge rates, you have no choice.

But as long as you realise these things take time, it will work.


If you have to have a battery mounted under the bonnet....OK..but things will be less ideal and you have some choices.

Do you connect both batteries in paralell, and feed the one under the bonnet from the dc to dc charger and loop onto the second battery.

Or do you install a VSR to charge the underbonnet and run the dc to dc charger to charge the rear

or do you just install a VSR and not bother with the DC to DC charger.

All reasonable choices.

Now remember these DC to DC chargers like all multistage smart chargers prefeer a direct relationship with a single battery...or a pair of batteries that have the appaerance of a single battery.

That said, the Dc to Dc charger will charge the two batteries one located under bonnet and one in the rear...but don't be under the illusion that it will be even...good heavy wire front to back will help.

The rear battery will fully charge, but it will lag behind the front battery.

The load will also not be shared evenly.

As long as you realise this and independently charge the rear battery from time to time this should not be a problem.

If you are running these two batteries in different places there is no need for them to be identical...but better for them to be of similar type.

Choices Brad that is what you have.

cheers