Van Conversion Electrics - Batteries, Solar and Wiring

The camper van electrics system can easily be the most confusing part of any conversion project.

Van Conversion Electrics - Batteries, Solar and Wiring

The camper van electrics system can easily be the most confusing part of any conversion project.

Figuring out what parts to buy and how it all fits together can be pretty tough.

Why is it that every campervan wiring diagram you find or YouTube video you watch seems to do it differently?

In this guide I’m going to run you through a campervan electrical system in 3 easy steps:

  1. Overview of the parts and how they work in (really simple terms!).
  2. How to easily calculate your battery, solar panel, fuse and cable sizes.
  3. How it all fits together inside your van.

I’ve attempted to make the following the advice on this page as easy to understand as possible. That said:

If you’re in any doubt about tackling the electrics in your van conversion, always seek the help of a professional electrician first!

How Do Camper Van Electrics Work?

If you start off by looking at complex campervan wiring diagrams it can feel like trying to understand another language.

We'll look at each part of a camper van electrical system in greater detail throughout this guide, but it's best to start with a simple overview.

As with any complicated project, break it down into parts and it soon becomes clear how it all fits together!

There are 3 basic parts to most campervan electrical setups:

👉 POWER INPUTS - solar power, van engine or a mains hookup.

👉 POWER STORAGE - leisure batteries.

👉 POWER OUTPUTS - 12v and 230v appliances and sockets.

This is how it typically fits together to create a complete campervan electrical setup:

van conversion electrical setup
Parts of a campervan electrical system.

As you can see above, we have the inputs bringing power into our system, leisure batteries to store it and appliances and sockets using that power.

Simple stuff really eh?

It's also reassuring to know that you don't need to add all the elements shown above.

If you want to keep things really simple you could just have a solar panel, battery, lights and a couple of USB sockets.

The brilliant thing about designing your own campervan electrical setup is you can completely customise it to fit your needs.

But, what are your power needs? Let's find out now...

Calculate Your Campervan Electrics Power Requirements

calculate your van conversion battery size
Click the link to get a copy of this battery and solar calculator spreadsheet.

Before you start ordering any electrical kit, it's best to get a clear idea of how much power you think you'll be using in your van each day.

This will help you to build out the best camper electrical system based on your own requirements and avoid spending more than you need to.

I've created a free Battery Size and Solar Calculator in a simple spreadsheet to help you work it all out.

It comes with full instructions on how to fill it in and get your personal leisure battery, solar and charge controller figures.

Once you've completed it, come back to this page to carry on building out your van conversion electrical system 🦾

Campervan 12v Electrical System Explained

Now we're all set to start building our camper van electrical system.

We're going to start with the 12v part of our setup. That's this bit from the overview image👇

how a 12v electrical system works in a van conversion

This will help us to understand the basics of campervan electrics and we can move on to the more complex stuff later.

We could just wire all the appliances and sockets (known as loads) directly to the our 12v leisure battery (the power source).

However with several things to wire up, we can be smart about it and use a blade fuse holder to power multiple 12v loads from a single point like this.

Basic campervan 12v system with blade fuse holder

This creates the hub of our van conversion 12v system!

We'll wire a positive input directly from the battery into the blade fuse holder and return a negative back.

These are shown as thicker lines in the diagram.

Each of our appliances will be wired into a separate space on the blade fuse holder.

Using some 12v twin core flex cable, we can connect up the positive (red) and negative (black) terminals.

The Common Negative Bar on the blade fuse holder (silver bit at the top) makes it easy to bring all the negatives (black wires) back to one central position.

If you don't have many appliances a 6-way blade fuse holder will do the job.

I'd recommend getting a 12-way blade fuse holder to future-proof your system, ready to expand it easily later on.

Wiring 12v LED lights together

Next, we can add in some LED lights to our 12v system.

Connecting the lights together in a string is known as wiring 'in series'.

This results in an uneven voltage distribution, so the light closest to the battery will be much brighter than the last in the series.

Therefore, if you have several LED lights across your ceiling, you’ll want to connect them 'in parallel' for the best results.

You do this by running single cable from your blade fuse holder with a positive and negative branching off to each individual light.

Here’s a basic diagram of what that looks like:

wiring campervan LED lights in series or in parallel
Wiring LED lights in series vs in parallel.

Adding Switches to a 12v System

Wiring any appliances directly into the power source as shown above means they will always be 'on'.

In the example of our LED lights, this would make it rather hard to sleep 👀

Some appliances, such as fans or heaters, will come with a built-in switch to control them individually.

For everything else, you might want to add a switch to the positive side of its connection to turn it on and off.

In the example of our LED lights, you can add in a switch to break the circuit on the positive side of the main power cable running from the fuse holder.

This approach would turn all the lights on and off together.

To control the lights individually, you’ll need to add in switches into the positive side of each branch.

Here's what both configurations look like:

Wiring in a single switch vs a switch per light.

To avoid the hassle of filling multiple switches, get some ‘touch sensitive’ LED ceiling lights. With these, you just tap the metal rim to turn them on and off.

How to Correctly Size Your Fuses

Fuses are essential for protecting any campervan electrical system.

They will 'blow' and break the circuit if there's too much current running through which could otherwise cause things to overheat.

It's vital that you size all the fuses in your camper van electrical system correctly to make it as safe as possible.

We'll start by looking at our 12v setup to get the hang of things 👍🏻

Fuses are rated in Amps so we need to work out how many Amps each appliance will be drawing from the leisure battery when it's active.

Refer back to the free Battery Size and Solar Calculator where all your 12v system fuse ratings will already be calculated, highlighted here in red 👇

how to correctly size fuses for a camper van conversion
Fuse rating in the battery sizing spreadsheet.

The spreadsheet is taking the total Watts that each appliance will draw, multiplied by the quantity column and divided by the Voltage.

Watts x Item Quantity / Voltage = Amps (x1.25)

The calculations shown are for 12v appliances only because our 230v items will run directly from an inverter.

More on that, and fusing the rest of your system, later on.

If we added a fuse equal to the load then there's a good chance it would blow each time the appliance is switched on.

To counter this, the spreadsheet formula multiplies the Amps by 1.25 to give a fuse rating 25% higher than the load.

Using Blade Fuses in a Campervan

Blade fuses are great to use as they easily push into the sockets in our 12v fuse holder.

They come in standard ratings and colours as seen here:

A selection box of blade fuses.

In our spreadsheet example above, the TV has a rating of 2.3 Amps so we can use a 3 Amp fuse here.

It is always best to go for the next fuse size up to be on the safe side.

Once you're ready, simply the appropriate blade fuses into the corresponding sockets on your holder.

It's a good idea to make a note of the appliance and fuse rating for all the positions in your holder.

This makes it easy to replace them and diagnose any future issues.

⚠️ An Important Note on Fuses for Fridges, Fans etc...

A fridge, heater or fan will need extra juice when it starts up compared to its regular power draw when in operation.

The 12v Dometic Fridge in my van draws around 6 Amps when it's running but the manual recommends a 15 Amp fuse due to the startup draw.

If I used a fuse below this, the startup draw could blow each time it clicks on!

When it comes to fusing appliances that have higher starting current, skip the spreadsheet and check the manufacturer's guidance.

We'll cover fusing the rest of your campervan electrical setup right after we've taken a look at wiring and cable sizing.

Correctly Sizing Electrical Cables for a Campervan

It’s vital that the cables and wiring you use in your van build are up to the job.

This cannot be overstated and you never want to cut corners when it comes to electrics.

Using incorrectly rated cabling can cause wires or appliances to overheat, potentially catching fire putting your van and you at risk!

To find the correct size for each appliance use this table 👇

Use the total loads in Amps from your Battery Size and Solar Calculator spreadsheet to see what size cable is required for each appliance.

Remember skip the spreadsheet and check the manufacturer's guidance for any appliances with a higher start up power draw such as fridges and fans.

As an example, our spreadsheet gives the 6 LED lights a draw of 1.1 Amps. 1 mm² cable would do the job here but we can use 1.5 mm² to be doubly sure.

Golden rules to follow when sizing your cables:

  • The cable you are using should always have a higher Amp rating than the circuit's fuse rating.
  • There's never any harm in going for a thicker cable to ensure your system is safe.
  • Amp ratings for cables drop if they are running inside conduit or insulation in your van.

It is important to allow for this difference as cables can't cool down as much if they are not in the open and the last thing you want is them to overheat!

Solid or Flexible Cable?

Electrical cable usually comes in two flavours, solid (single core) and flexible (multicore).

Sold copper cable is often used in household electrical systems and isn’t suited to van builds.

Flexible multicore cable on the other hand is ideal for van builds. It's much easier to work with when installing and will better deal with the regular vibrations of the van.

Flexible multicore (twin) cable.

Using cable with rubber sheathing will also help to ensure it’s well protected.

Using PVC Conduit

To make life easier when installing your cables, first run some PVC conduit through the framework of the van.

PVC Conduit

It’s relatively cheap to purchase and will protect your cables from getting caught or rubbing on any sharp edges of the metalwork of the van.

It also makes it way easier to run cables unhindered to where you need them, giving you the ability to run additional cables once your build is finished.

Campervan Electrical Wiring Diagrams

Now you have a better understanding of how the 12v part of the setup works, we can use this fresh knowledge to build out the rest of the system.

A wiring diagram is the easiest way to represent any campervan electrical system on paper.

We're going to begin to sketch one out now. You can then adapt it to build out your own system.

Let's start with the 12v system bit specked out in full.

Our 12v wiring diagram includes:

  • The calculated cable sizes (shown in mm)
  • The calculated blade fuse sizes (shown yellow in in amps)
  • A fan, fridge, 4 LED lights and 2 USB sockets
  • Switches for each appliance
basic 12v campervan wiring diagram
Basic 12v wiring diagram with wire and fuse sizes.

We can now connect our 12v battery (or multiple batteries) into the blade fuse holder to give the system some power.

To calculate the correct cable and fuse sizes for this part of our van conversion electrical system it's simply a case of adding all the maximum loads from our blade fuse holder together.

In our example diagram they would be:

USB Sockets - 6.2 Amps
Fridge - 15 Amps...

Coming Soon...