Battery Controllers

Hi Wayne and Sally,

Why so much diversity in answers to what seems a pretty simple question? Because of different physical layouts with different wiring and wiring losses, coupled with different usage patterns, different batteries........

In the two cases you mention, there is an existing auxiliary battery mounted in the engine bay with a controller to connect it in parallel with the cranking battery once that has come up to a "charged" voltage. Since this aux battery is mounted close to the cranking battery, this should work well and both should be properly charged (subject to being similar types).

Case 1. 200 Ah storage in a camper trailer. Because of the length of wiring and the unavoidable resistive losses, I would opt for a 20A or 30A dc-dc charger mounted close to the batteries in the camper, and would use heavy wiring (say 6 B&S twin) to couple to a SECOND controller in the engine bay to connect to the cranking battery. (Without that 2nd controller the trailer batteries will be charged from the under-bonnet aux battery while the engine isn't running. Here I'm assuming that most charging will be by the alternator - if though you are likely to camp for more than a few days without running the engine, we have to consider solar, opening up a whole new (expensive) scenario.

Case 2. 200A storage in the back of the ute. Similar constraints, though using heavy cabling, it should be possible to parallel these batteries with the under-bonnet aux battery and use the existing controller, without the dc-dc charger. Again there are constraints - all these should be batteries of similar chemistry, and characteristics. This arrangement is not ideal as the temperature of the alternator and cranking battery will influence charging of all these batteries. Nothing is simple!!

You may find Electricity for Camping a useful read.

Cheers

John

Where there is an auxiliary battery mounted some distance from the alternator it is best to use a dc-dc charger such as the Redarc BCDC-1220 located close to the remote battery. This device will accept input voltage as low as 9 volts yet still charge the battery at up to 20amps. It also acts as an isolator to prevent back feed from the auxiliary battery and is controlled by the ignition to only charge when the engine is running. As well as that, it is also a 3-stage charger to optimise the battery charging. A versatile device.

Although the BCDC-1220 will operate with as little as 9 volt input, it is still desirable to use cabling heavy enough to minimise volt-drop losses as much as possible.

A second larger DC-DC controller like the Redarc Redarc 12/40. This should be mounted close to the batteries. I am using the Redarc BMS 12/15 to manage 2 x 140 A/H Powersonic AGM's in the rear pod of the ute. A 12/40 sits over the front auxillary. (Both the BMS and the 12/40 have inbuilt MPPT solar controllers so you can plug your solar panels directly into them whilst stationary).

Have a read of the power management section of my ute build blog.


Cheers Mick

Hi everyone,

Thank you for some very informative answers to my original question and all the answers are food for thought

I understand that there are a large number of variations to a theme ...... all good.

Maybe at this point I should re-qualify the question ..........

.............. and ask

What do you use to control the power output to remote location batteries, "from under the bonnet"??

Regards,
Wayne & Sally.