How To Set Up A 12V Dual Battery System In A 24V Vehicle

Last time, Andrew and Peta Murray from Top Wire Traveller outlined what accessories are available for your small 4x4 truck. This time, they explain how to set up a 12V dual battery system in a 24V vehicle…

Most trucks run 24V electrical systems. This can lead to lots of head-scratching when you’re trying to install a dual battery system.

What should you do? Maybe you should install a 24V dual battery system?

No, then you can’t buy standard 12V devices. And you might have a perfectly good 12V air compressor, a Pure Sine Wave Inverter or a UHF radio from your previous vehicle. You certainly don’t want to purchase these again.

Many electrical components aren’t “24V-friendly”. Just one example are USB sockets. While you can readily buy USB sockets suitable for 12V input, 24V-compatible sockets aren’t so easy to get hold of.

So the obvious decision is to install a 12V system. But how do you integrate it with the truck’s 24V electrical system?

As it turns out, the setup is actually pretty straightforward… if you do it right up front. We’ll start with the basics.

First things first

Think of your dual battery system as a box, floating in space. Grab this box and anchor it to your truck. The box needs power, so give it solar power, 24V from the truck and maybe even the ability to plug in 240VAC from mains power.

Now, what’s the easiest way to get 12V power into the cab? Supply it from the dual battery system.

Sure you can add 24-12V reducers. However, the cab is where you’ll need most of your 12V supply. Think USB outlets, additional lighting, an inverter and even your UHF radio.

By doing this, you don’t need to modify the truck’s electrical system. Instead, you’re simply adding a 12V system over the top of the truck’s existing 24V electrical system.

What devices do you need?

Step one is to figure out what devices your dual battery system will be powering. I won’t go through this process here. Rather, go here for some excellent tips and ideas on sizing your dual battery system.

One tip before we move on. You always end up with more electrical components than you first thought. So allow for expansion. For example, if you think you’ll be running three different 12V accessories, then make the system large enough to run six.

Oh, one more tip. Always add a spare Anderson plug outlet. We have one rated at 60A. This runs our large portable air compressor, and occasionally a portable water pump. We also have a second Anderson plug outlet rated at 40A “just in case”. You never know when you might need it.

Now for the tricky bit. How do you use your truck’s 24V electrical system to power your dual battery system?

Keeping It Simple

You’re probably imagining some complicated setup involving voltage reducers and isolators. However, the solution is actually quite simple.

You see, REDARC have a range of in-vehicle battery chargers capable of receiving an input voltage between 9 and 32V. Problem solved!

These chargers continually monitor your battery’s State Of Charge (SOC). Based on SOC, the chargers convert the input voltage into the output voltage needed at that time.

You simply “tell” the charger the size and type of battery (e.g. AGM, lead acid, even Lithium depending on the model of the charger) and away it goes… happily keeping your battery’s charge optimised at all times.

Some of these chargers also accept a solar input, prioritising solar power. And most also accept input power from smart alternators, depending on the model.

They all act as isolators, monitoring your start battery’s voltage and isolating it once a low threshold is reached.

The best part is, the unit knows whether the vehicle’s system is 12V or 24V. So you don’t need to worry about a 24V vehicle system being depleted down to 12V.

Stepping Up

Moving up a level, REDARC’s battery management systems (BMS) provide several additional features. Firstly, there’s the option of plugging 240VAC mains power straight into the unit. So the unit instantly becomes a 240VAC - 12V multi-stage battery charger.

It can also handle variable voltage alternators.

You can wire it to isolate non-essential loads like inverters, once a low voltage threshold is reached. This is handy when you’re running a fridge for example. With non-essential loads being switched off automatically, you can keep the fridge going for longer.

And lastly, the BMS has a Remote Monitor. While the monitor may sound like a gimmick, it’s not.

Find a convenient spot to mount this and you’ll instantly know the State Of Charge (SOC) of your dual battery system. You can see at a glance how your system is performing.

Installing a 12V dual battery system in a 24V vehicle seems complicated at first. However, use the right components and it’s actually quite simple.

Eliminate a whole range of components by installing one charger or battery management system. The result? A simple system that will operate reliably for many years.

You can follow Andrew and Peta’s outback travel adventures via their website and on Facebook, Pinterest and YouTube.