Everything You Need to Know About Setting up Motorhome Electrics

July 26, 2021 in Tips for Owners, Motorhome Maintenance & Tips for your Motorhome

The idea of wiring and installing the electrics, for most people doing a campervan conversion, can be daunting. There is, undeniably, quite a lot to think about when it comes to planning your DIY camper electrical system. 

Doing your online research can be overwhelming when it comes to slightly more complicated aspects, which you want to get right. There’s so much new information out there; van build blogs, Reddit threads, Youtube videos…and though you can learn a lot about electrical systems, wiring and circuits from these, it’s time-consuming to try to absorb it all! Plus, doing so might just leave you with a raft of your own questions. 

Luckily, we have put a lot of time into researching and collecting all the information you’ll need into one concise, diagram-filled post. The reality of doing this yourself means that there is some research you need to do yourself - mainly familiarising yourself with your own vehicle so as to plan your wiring properly. But we’ll point you in the right direction. 

We’ll start with a mega list of all of the components, then break down the installation into its major parts. There are a few diagrams in there to help clear things up, too. Finally, we have lots of handy tips for you to remember when installing your campervan electrical system, which will save you some stress down the line!

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1. Components

You may want to take your time and go through this list, finding the best bits and pieces that suit your needs and your budget. It’s recommended to buy online if you have the time to wait for delivery, as you can save yourself some money as compared to shopping in the major hardware stores. 

We will revisit the key components outlined below, so if you’re not sure what they do yet, don’t worry!

If assembling these pieces seems like it will be too time-consuming, don’t worry. Over at Wired campers, they’ve carefully assembled complete kits for a campervan electrical system. For a pretty penny, these will provide you with a 12V and 240V split system ready to go in your van, pre-wired for quick fitting. You can find out more about that here. Alternatively, you can head to eBay for similar kits

2. How it works

The actual lay out of your components, how you wire them together depends entirely on your own van. It depends on the size, layout, appliances you want to power, materials you’ll be running it through (such as insulation) and the size of the components you choose. 

However, there are some general rules of thumb that you’ll want to keep in mind. 

  1. Power comes in via a split charge relay (and any other inputs if you have them, such as a solar charge pack).
  2. Power goes out via a fuse box and an inverter. It’s important to make sure the fuse box is the closest thing to the battery - this protects your van from catching fire if the wire should short.
  3. If you have a switch for your inverter, this comes next. Some people protect the inverter with an inline circuit breaker, too. You just have to figure out the maximum current that you want to draw from the inverter, and order the equivalent breaker to protect it.

Some van conversion bloggers include helpful diagrams like this one to help you get an idea of layout. We’d recommend designing one of your own early on in the process!

3. Leisure batteries

Deciding how big a battery you’ll need to power your motorhome electrics is easy, but you might want to draw up a little spreadsheet. Input all of the appliances you’re going to want to use, and then calculate the amp hours for each by using the following, simple equation. 

Watts / Volts = Amp Hours

Once you have the Amp hours 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 of Amp hour usage per day. 

Remember, you should never let your batteries discharge more than 50%. And, if you don’t want to rely on having to drive around each day so our split charge relay (we will come back to this device) can charge your batteries, go for more than a day’s worth of energy. 

For example, if your total maximum is 110Ah/day, then you will need a battery that can provide more than 220Ah/day. For example, 2x of these 120Ah SuperBatt lead acid batteries will give a total of 240Ah. 

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4. Split Charge Relays

Split charging is just the term for simultaneous charging of the vehicle starter battery and the leisure battery from a common charging source. In your motorhome, this source is usually the vehicle alternator, which is in turn powered by the engine. It could also be a  solar or wind powered re-charging system or portable generator, if you wish to add those into your DIY camper electrical system.

Split charge relays are devices that connect the starter and leisure batteries only when a charging source is operating, and electrically isolates them otherwise, ensuring that the use of one battery does not draw current from the other. This is important, as you need the starter battery to be isolated, so the engine can always be started, but you also don't want the leisure battery to be accidentally drawn upon when starting the engine because dedicated leisure batteries are not designed for high current output over short periods of time and can be damaged. 

You can get a manual split charge relay, or a more modern alternative is a Voltage Sensitive Relay (VSR) which intelligently monitors the incoming voltage. Once the input voltage reaches a certain level, the device uses an electromagnet to pull a set of contacts inside the device to make or break a circuit. This is the most recommended option, for several reasons. 

They’re simple to fit, reliable, and relatively cheap. Many voltage-sensitive relays are dual-sensing, so when voltage exceeds the activation level, it allows power to flow back into the starter battery. Some devices feature an emergency manual override switch, so the user can manually activate it for a short period. This feature is useful if the starter battery has a low charge level and needs a brief boost of power. Some more intelligent VSRs can monitor the voltage of the vehicle over a long period. More data of the electric system is then used to activate the relay at a more accurate voltage level. Vehicles can suffer from voltage fluctuations, so this feature helps eliminate unwanted opening and closing of the relay.

This blog features a good summary of split charging options if you want to investigate further. 

5. B2B Chargers

If your leisure battery is bigger than 220Ah, a battery to battery (B2B) charger is necessary. They’re more effective, in general, than split chargers, both at passing more energy through from your starter motor and at using it more efficiently. You can get different size B2B chargers, and you may need to get a certain one if your van is Euro 6 or above. The 60 amp Sterling B2B is widely considered to be the best, and is also compatible with Euro 6 engines and above. 

6. Inverters 

If you want to charge your laptop or use other household AC appliances (ones that require a 3-pronged wall outlet), you’ll need an inverter. It takes the 12V power from your batteries, and converts it to 230V, so that these can be run. 

The 2 types of inverter available are:

  • 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.

One thing to note is that some cheaper inverters create a square wave rather than a sine wave. Some appliances, such as TVs, don’t work as well on square waves, so invest in the right products early on in the conversion process.

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.

Double this, to future proof your electrical system. 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. And, you’ll have some room to run more powerful appliances in the future. 

Bear in mind that not every 230V appliance can be used with an inverter. Good inverters have a mechanism built in which will stop it from providing power to an appliance that exceeds the total wattage in order to protect the inverter, but not all inverters will have this so check every appliance before plugging it in to your campervan electrical system!

And, if you’re still not sure how big of an inverter you need, these guys have made a very handy online calculator! 

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7. WiFi

If you’re thinking of getting mobile internet on the road too, there are a few options for motorhome WiFi. A very popular choice is a WiFi dongle, like this EE one. As long as you have phone signal, you’ll get decent internet (though not necessarily high speed). Do some research to find out the best providers of network coverage if you need to access the internet most of the time on the road, and buy one of their mobile internet SIM cards to use with the dongle. Prepaid SIMs are good, but be sure to read the small print (you might have only so long to use the data before you lose it). If you use it often, paying monthly isn’t a bad idea. Be sure to buy the right size SIM for the dongle, too. Many take nano or micro-SIMs. You might have to re-activate it after a few months of no use, too. Again, just read the instructions thoroughly. 

We think the best choice of mobile WiFi for motorhome use is one used in combination with a motorhome wifi booster. It’s an antenna or small box which, once fixed to the roof of your motorhome/ camper, boosts the WiFi signal it receives, allowing you to get a better connection. It can be fixed permanently, or by sucker (remember to take it down before you drive off if you sucker it on!). What’s good about this system is that it can be powered by either 12v or 240V, and it’s great for boosting mobile wifi, for example, from your dongle, when wild camping or on campsites.

You can buy combination systems, like the Kuma system, for a complete, especially-designed motorhome WiFi system. Kuma do two main types- a 4G wifi dongle which comes with an antenna to improve the signal. You can put any SIM card in this (just make sure it's a data sim). Or, they do a WiFi booster with antenna and router. Both facilitate up to 5 devices to be connected to the box at once, and you can use both systems together to make life even easier.

8. Wires

Choosing the right wire sizes is an important step: if your wires are too thin, it can be a significant safety hazard within your DIY camper electrical system. If your wires are too thick, you’ll be spending more than you need and your wiring will be harder to work with. Base your choice of wire size on the amount of current going through the wire and the length of the wire run. Use a wire size that’s thick enough to safely handle the electrical current without experiencing too much voltage drop. Wire gauge conversion charts are a very useful tool for helping you to get maximum electrical efficiency, practicality and safety with the appropriate wires. 

9. Tips

Here are some important things to remember, to make installing and using your motorhome electrics easy and problem-free. 

  1. Go for 12v appliances rather than 240v when you can - they will be more efficient (remember, if you’re using 240v appliances, you’ll also need an inverter, and these also use energy).
  2. Make smart choices when picking electrical appliances for your campervan. For example, more cold air is lost when opening an upright fridge compared to a box fridge (because cold air sinks).
  3. Invest in a good power management system, so you can control and monitor your campervan electrics.
  4. Use quality marine grade components as they are built to withstand tough environments.
  5. Isolate each component using fuses or isolating switches to protect the battery from voltage and current spikes. 
  6. When doing the rest of the conversion jobs, remember to disconnect the battery you’ve installed in order to avoid any shocks!

Goboony campervan electricity h2 motorhome electric system

Hopefully, this blog will get you off to a sure-footed start when it comes to installing your motorhome electrics. Once you’ve sized and decided on all the components, and planned how you’ll wire it, the actual installation isn’t so hard. But, get this more intricate stage of the conversion done early, as you can find suitable places for things like the battery box when you’re looking at the bare bones of the vehicle. 

Once everything’s hooked up, then you can enjoy the conversion, by sitting back and streaming using the best mobile wifi for your modern motorhome, or being able to work on the road and spend extended time away!

Looking to complete more DIY campervan upgrades? Maybe you can expand your campervan storage space next!