How to: wire a camper van electrical system

Updated: Aug 26

Wiring and installing the electrics is arguably one of the most complicated and daunting jobs in your van conversion. We spent a long time reading blog posts and forum comments and watching YouTube videos to try and figure out exactly what we needed to know. Here we talk through everything we did in our own Sprinter camper van electrical system, the products we bought, and everything we learnt along the way, in the hopes it might be able to help others out at the same point in their van build!

Hopefully this post will help you answer questions like...

  • What components do you need for your van electrical system?

  • How to size your van electrical system

  • How to wire your van electrical system

  • What inverter should you buy for your camper van?

  • How to wire a 2 way switch

DISCLAIMER: We are not electricians, and everything we did in our own van we figured out by researching online. We hope the information is useful to you, but is not professional advice. Electricity can be dangerous, and if there is anything you are not sure about, make sure to consult an electrician.

What components do you need?

Below is a list of all of the electrical components we bought for our van build. We'll go into a little more detail later as to how we decided on battery size, number of solar panels, and the size of our inverter.

Main components:

Solar setup:

Lighting components:

Wires, connectors & wiring accessories:

  • 150A bus bar

  • 3x kill switches

  • 2x Arctic F12 PC fans

  • Double rocker switch and pattress box for fans

  • 4x midi fuse holders

  • 125A, 2x 100A & 50A midi fuses

  • 3-40A blade fuse set

  • 4x plug sockets & pattress boxes

  • Crimping tool

  • Wire strippers

  • 1m of 35mm² red wire & 1m of 35mm² black wire

  • 4m of 25mm² brown wire & 4m of 25mm² blue wire

  • 2m of 16mm² earth wire

  • 5m of 6mm² brown wire & 5m 6mm² blue wire

  • 100m of 1.5mm² 2 core blue/brown wire

  • 100m of 1mm² 2 core blue/brown wire

  • 20m of 1.5mm² 3 core cable + earth (for wiring 2 way light switch)

  • Lots and lots of yellow, blue and red butt connectors

  • Lots and lots of 16mm to 35mm / 6 to 12 cable lug eyelets

How to size your van electrical system

The amount of electricity you expect to use in your van conversion will affect the size of battery you need. We worked this out by making a list in a spreadsheet of all the appliances we planned to use in our van, and then calculating the Amp hours for each appliance using the following equation:

Watts / volts = Amp hours

Where the volts equal 12V, the voltage of your batteries, and watts equal the wattage of each appliance. Once you have the Ah for each product, you will need to multiply by the number of hours you estimate the product to be in use for each day. Adding all of these together will give you your total estimate Amp hour usage per day.

We calculated our absolute maximum as 110Ah/day. As you should never let your batteries discharge less than 50%, you then need to double this, which equals 220Ah.

As we didn't want to rely on a) our solar panels fully charging our batteries each day (in case of cloud/rain) or b) having to drive around each day so our split charge relay could charge our batteries, we were keen to go for larger than a day's worth of energy. In the end we went for 2x 180Ah Varta flooded lead acid batteries which gave us a total of 360Ah.

We found this post from Mowgli Adventures incredibly useful in helping us to decide what size batteries we would need!

Once we had decided on battery size, we then worked out how many solar panels we would need in order to charge our batteries.

Before, we worked out the Amp hours that we would be using with all of our appliances. To work out the size of our solar panels, we needed to work out total watt hours:

Watts x hours = watt hours

So if a 30W product is in use for 3 hours, the total watt hours would be 90. Once you have worked out your total watt hours for all your products, you'll need to divide this by the average amount of full sunshine your solar panels are likely to receive in a day.

We worked out our maximum would be 1500Wh, so dividing this by 6 hours of sunlight we worked out we would need 250 watts of solar panel power. We decided to buy 3 100W Renogy solar panels to give us 300 watts of power.

We found this post from Gnomad Home really useful for helping us figure out how many solar panels we would need.

For details on how to install your solar panels, have a read of our solar panel blog post.

Our wiring diagram

Our campervan wiring diagram

Our system consists of:

  • Power coming in via a split charge relay and a solar charge controller

  • Power going out via a 12V fuse box and a 800W 12V inverter

We chose to install an inverter so that we could have 230V power in our van. This meant that we could wire in standard plug sockets so we could charge laptops, phones, and anything else mains powered we might want to plug in, and it also meant we ended up wiring in 230V lights. Below is a list of the appliances we've wired into our camper van:

12V appliances:

  • Lights in the boot

  • 2 fans

  • Fridge

  • Water pump

  • Water level sensors

  • Diesel heater

230V appliances:

  • 3 double plug sockets

  • 1 single plug socket

  • 10 3W spotlights

  • Fairy lights

  • Sparker for hob

When deciding what fuse sizes and wire gauge to use with all of our different appliances, we found some really useful posts online:

Important note about split charge relays

We have a 2013 reg Mercedes Sprinter, which means that we could not use a standard VSR (voltage sensing relay) to charge our batteries via our alternator. Because we have a Euro 6 engine, the alternator voltage drops below 12V after around 30 seconds to conserve energy. We needed to purchase a non-standard split charge relay in order to be able to charge from our alternator.

There are 3 main options to pick from. Sterling and CTEK both have battery to battery chargers that are compatible with Euro 6 engines, but these are ~10 times more expensive than a standard VSR and almost 10 times the size too! We opted for the third option, which is a new product from Durite, called the 0-727-43 Split Charge Intelligent VSR (catchy name!). It is only double the price of a normal VSR and actually smaller! We'd definitely recommend this if you have a Euro 6 engine. For more details about the Durite 0-727-43 VSR, have a read of our Durite Smart VSR blog post.

Our new Durite Smart Relay for our Euro 6 engine in our van conversion

What inverter do you need?

Your inverter will take the 12V power coming from your batteries and convert it to 230V so that you can run regular AC appliances such as laptop chargers.

There are 2 types of inverter available:

  • Modified sine wave

  • Pure sine wave

Modified sine wave inverters are much cheaper than pure sine wave inverters, and should work fine for around 95% of AC appliances. Occasionally modified sine wave inverters can make a buzzing noise when certain appliances are plugged in. We went for a modified (quasi) sine wave inverter.

Depending on what you plan to use in your van will decide what size inverter you need. The calculation you will need to do for each appliance is:

Voltage x amps = watts

Once you have done this calculation for every appliance you plan on running on 230V in your van, you will have the total watts that could be in use at one time.

Then, to play it safe, and future proof your electrical system...double it. The number you now get is the minimum watts you'll need out of an inverter to power all of your appliances at the same time.

We worked out our total watts at 350W, so we went for the Sterling 800W quasi sine wave inverter. This way if we ever want to run more powerful appliances in our van, we still have plenty of leeway.

However, it's worth noting that not every 230V appliance will be able to be used with an inverter. A good inverter will have a mechanism built in which will stop it from providing power to an appliance which exceeds the total wattage in order to protect the inverter, but not all inverters will have this so make sure you check every appliance before plugging it into your van.

How to wire a 2 way light switch

A 2 way light switch controls a light from 2 different sources. We were keen to wire our 4 bedroom spotlights and fairy lights into a 2 way system so that we could control them both from the 3 gang light switch by the van door (which also has a 1 way switch to control the main 6 spotlights), and from the 2 gang light switch by our bed. We knew this was making things complicated for ourselves...but we've never been good at making things easy!

Below is a wiring diagram for how to wire a 2 way switch. As well as running a 'power' wire from your 12V fuse box or your inverter (depending on if you have 12V or 230V lights) to your switch, and wire from your switch to your lights, you will also need to purchase 3 core + earth cable to run between your light switches. This has a black, grey, brown and earth wire. You will need to connect the negative of the power wire and the negative of the light wire together outside of the light switch.

Wiring diagram for wiring in a 2 way light switch in a van conversion

We hope some of the information in this post was useful, and if you have any questions about our setup please get in contact!

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