4WD 12V Electrical Setup; what do you need to know?

In the past, if you had a secondary battery with a manual isolator that ran a 12V fridge, you had a solid 4WD 12V electrical setup.

Today, its not uncommon to see people with hundreds of amp hours of lithium batteries, 3000W inverters, AC and DC chargers, air fryers, coffee machines and a million other appliances in the back of their 4WD.

Times and technology have moved considerably, and in this post I want to extensively cover every type of 4WD 12V electrical setup, starting from the absolute basic and moving to the expensive, complicated and fancy options.

Electrical box in our Dmax
4WD 12V systems have changed dramatically in the last few years

What 12V gear do you actually need?

Before we start, I want to make a point of mentioning that the perfect 4WD 12V electrical setup is the one that does what you need it to.

What’s the point of a fancy coffee machine, induction cooktop and big battery system if you aren’t even going to use it, or you don’t really need it?

I’ve always been a big believer in buying, and building something that does what you need it to. With that in mind, here’s the various levels of 12V setups in a 4WD:

Basic temporary 12V system

The most simple, and portable 12V battery system is something that is attached to a battery box, which you strap down when in use, and then unplug and pull out when you leave.

For some people, this is literally a secondary battery, with a couple of USB and cigarette outlets, and maybe even an Anderson or two. To charge the battery it can be as simple as an Anderson plug from the main battery, or it might include a DCDC charger.

You can set these up to take power from a solar panel (via a regulator), and you have the perfect, portable battery system that will run your appliances when you are away and it can be removed when you come home.

Battery box in use
There’s a heap of battery box’s on the market today, which make a great portable solution

Basic permanent 12V system with a secondary battery and isolator

A lot of 4WD’s will have a secondary battery installed either under bonnet, or in the back of the wagon or Ute.

On the cheap end of the scale you have basic dual purpose batteries, or AGM batteries that are designed to have small currents draw from them over a long period of time (like a 12V fridge).

Radiator cap spare
A fairly standard dual battery setup in our 80 Series Land Cruiser

If the battery is permanently installed, it will usually have an isolator in place to stop your cranking battery from being flattened when you are parked up.

This can be in the form of a mechanical isolator that you physically switch off when you pull up, or it can be a voltage sensitive one like the Redarc SBI, which looks at both battery voltages and automatically disconnects and reconnects as needed.

Redarc VSR
The Redarc SBI12 that was in our 80 Series Land Cruiser

If you have this system, you’ll normally have some outlets for running your appliances. Cigarette plugs work (but they are pretty useless), with Andersons being a lot better, and the Engel plugs working well too. These days USB outlets are hugely popular too.

From there, things get more complicated with the addition of DCDC chargers, and we’ve got an article to help you decide whether you need one; Do you need a DCDC Charger?

Adding an inverter

If you want to run 240V appliances, an easy way can be to add an inverter. A big inverter will run almost all of your household appliances, but you need to size it to suit your batteries maximum discharge rate.

For most 4WD 12V setups in regards to AGM batteries, you are looking at a maximum of 10 – 30 amps, which is only about 400W, and won’t run much beyond an 18V charger, laptop charger, camera batteries and small appliances.

For many years we had a 150W, and then a 300W and 400W inverter that we used for camera batteries and odds and ends (and 240V fans when it was really hot).

You can buy 12V chargers for most applications, but if you want to run a heap of different things then buying 12V chargers for everything is a problem.

Enerdrive Inverter
Our 400W Enerdrive Inverter that we used for lots of light duty 240V appliances

The inverter should be wired to the battery with a fuse, and you should run items directly off the inverter.

If you want power points wired up, it has to be done by an A grade electrician with the right equipment in place (and installation process) to ensure no one can get killed playing with it.

Renogy inverter installation
We’ve now got a 2000W Renogy inverter (temporarily installed) and lithium batteries

If you aren’t sure, here’s what size inverter do I need?

Upgrading to lithium

There’s been a ridiculously quick movement from Lead Acid batteries to Lithium batteries, and when you take some time to compare the two together, its not hard to see why. Dollar for dollar, lithium comes out way further in front, and its got a whole realm of other benefits.

We’ve got a lithium battery buying guide that is worth a read, and we actually built ourselves a 230aH DIY Lithium battery which has been pretty amazing.

DIY lithium battery
Our 230aH DIY lithium battery that we are running in the Dmax

If you go to lithium though, you need to ensure the components all work together properly; most require a lithium profile to charge correctly, and its not common to charge them from the alternator directly (although some do suit this).

We replaced our Projecta DCDC which didn’t have a lithium profile (and was broken anyway) with a Renogy DCDC, and so far its doing a great job.

Renogy DCDC installed
The new Renogy 50 amp DCDC installed

What do you need to think about?

Ultimately, there’s a heap of things that you should consider before you do anything with a 4WD 12V system:

What do you want to run?

The starting point should always be what appliances you want to run. If its a basic 12V fridge, then your power demands are going to be vastly different to someone who wants to run a coffee machine and induction cooktop.

Start with the amount of power you are going to consume each day, and then work out how you are going to supply that power (as in batteries and inverter), and how you’ll recharge the power.

You want to be sure that you’re not running your 12V batteries down too low and damaging them. We’ve got a post to help you understand this better, called How long does a 100aH battery last?

240V sandwhich press
If you want to run a toasted sandwich machine, you need a decent electrical setup to handle the current draw

How often are you going to be moving?

Everyone travels differently. Some people rarely stop in a place for more than 8 hours at a time, and are always on the move.

If you are driving all the time, you can have a very different setup to someone who wants to pull up at a camp site and not move their vehicle for 10 days. 

Your vehicle can supply a fair amount of charge (normally), but if you aren’t driving much, then you need solar to do the generation.

Driving to Frys Flat Campground
If you rarely drive your vehicle, then alternator charging is very limited

Are you happy to set up portable panels?

As time has gone on, I’ve become pretty lazy, and would much rather a permanent roof rack solar panel setup, which is always running and doing its thing, and requires no setup.

There’s no doubting that portable panels are a fantastic option in some cases, but are you happy to set them up each time you pull into camp, and pack them away when you are done?

If you’re looking at solar panels vs solar blankets, we have a post for that too.

Do you have room for permanent panels, and can you fit enough to supply your demands?

Portable panels
Portable panels can be really good, but they are almost always a pain in the backside

What do you want to spend?

12V electrics aren’t cheap, and they can be really expensive once you start adding quality, trades level labour into it too.

Whilst you’d get away with $500 for a basic dual battery setup to run a fridge, a lot of people are spending up to 15 grand on fancy lithium batteries, DCDC chargers, solar regulators, AC chargers, shunts, inverters and a whole heap of other gear.

Obviously, you’re going to tell me that you want to spend as little as possible, which is where things get hard; do you risk a cheaper brand in the hope that you’ll save some money, or pay the premium for a well known brand that is going to back you up every day of the year?

In the end, you’ll have to consider the above points and come to a compromise. You can’t run an induction cooktop, microwave and coffee machine off a $500 setup, but maybe you then decide you don’t actually want the heavy power drawing appliances.

Induction cooktop on the Dmax
We can run an induction cooktop off our Dmax, but do you really need to?

What 12V setup do we have?

Our Reconn R2 has 720W of solar on the roof, with a 200W kings solar blanket, and 340aH of Renogy Lithium Batteries.

It’s got a 60 amp Renogy MPPT charger, as well as an Enerdrive DCDC for the alternator and solar blanket charge, and has a 3000W Renogy inverter in use too.

Renogy upgrade
Our camper trailer electrical system

We use this to run induction cooking when the sunlight is good, an 82L Evakool Freezer, lights, water pumps and other basic appliances.

Our Dmax is setup as a completely separate system, and runs a 230aH lithium battery, with a 200W solar panel on the top that is permanently mounted.

This runs our 85L Bushman Upright Fridge, lights, an induction cooktop as needed, and charges all of our camera gear through a 2000W Renogy inverter.

New inverter
Our Dmax lithium battery and inverter at the front of the canopy

This was a good compromise for us; it was as budget friendly as possible, does what we need it to and overall we’re really happy with it.

We could easily have ditched the big inverter in the Dmax, and run a smaller lithium battery, but it gives us some redundancy when the sun doesn’t shine like you’d hope it would.

What 12V system do you run? Are you happy with it?

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