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DIY Camper Electrical System

So you’re at the stage of planning your DIY camper electrical system? Awesome! Nervous? Excited? Dreading it? Confident? Overwhelmed? Doubting yourself? All of the above. I get it, we’ve been there. Hopefully we can help.

DIY Camper Electrical System

In this blog post I’m going to attempt to condense all the most important things we learned and implemented in building our van conversion electrics. We’ll be detailing all the components of our DIY campervan electrics, including a detailed campervan wiring diagram.

12v campervan electrics

Plus lots of useful information on how to size your batteries, solar panels, fuses and cables.

Disclaimer: We’re not electricians. Our skills are completely self taught through hours of research. We hope you find this information helpful but do bear in mind it is not professional advice.

Electricity can be dangerous so do consult a qualified person if you are unsure.

Campervan Electrics Explained

It’s easy to get overwhelmed when designing your campervan electrics. But when it comes down to it, it’s really all just about calculations. So as long as you can do some basic maths there’s no need to be intimidated by it, or guessing at anything.

At the heart of it you have your leisure battery bank. Feeding that will be a mains power hook up, or solar panels, or battery to battery charger, or a combination of those.

Initially we designed our DIY Camper Electrical System to be completely off grid and mostly renewable and it was like that for a couple of years. It was only later, that we added a mains electric hook up for when the weather was terrible and we were stationary for long periods.

campervan electrical system
campervan electrics explained

But our main power supply is still through our solar panels, with a battery to battery charger as a top up and mains battery charger for back up when there’s very low light and we’re not moving around much. Then power then goes out via our 12V fuse box and 500W inverter.

Depending on the electrical appliances you want to use from your camper conversion electrics you may opt to not install an inverter and 230V sockets.

Because we live and work in our van full time, we need ours to plug our laptops into. But pretty much everything else runs off 12V campervan electrics.

Still confused? Our self build campervan wiring diagram should help.

Campervan Electrics Diagram

Campervan Wiring Diagram

Don’t worry if you don’t totally understand all the individual elements just yet. We’ll go into each in more detail in the coming sections. Including how to correctly size batteries, solar panels, cable thickness and fuses.

This is just to give you an idea of the flow of our campervan electrics.

Campervan Electrics Components

Please note that for many of these campervan electrical system parts we recommend purchasing from a specialist supplier rather than Amazon to ensure quality and safety.

12 Volt Planet and Simply Split Charge have great online shops. And we can personally vouch for them being super helpful when contacted over the phone or email if you need further clarification on the right parts for your DIY camper electrical system.

We sent 12 Volt Planet our wiring diagram and they were kind enough to give it the once over before we set about ordering all the parts. The ‘Knowledge Centre‘ on their website was crucial to the designing of our camper electrical system and they also have a YouTube Channel with lots of super handy information.

Here’s a complete parts list for our camper electrics system to get you started on your design.

Solar Setup

ComponentQuantityProduct Link
150W 12V Photonic Solar Panel3View Now
Photonic Universe 40A MPPT Solar Charge Controller1View Now
Double Pole Isolator (25A)1View Now
Cable Entry Housing1View Now

Main Elements

ComponentQuantityProduct Link
12V 110ah AGM Lead Acid Batteries3View Now
Sterling 60A B2B Charger Kit1View Now
Victron 12V 500W Pure Sine Wave Inverter1View Now
12 point 12V Blade Fuse Box1View Now
Photonic Universe Remote Display1View Now
Victron 30A Mains Battery Charger1View Now
Mobile Mains Hook Up Unit1View Now
UK to EU Charge Cable Adaptor1View Now
Campervan to Mains Adaptor Cable1View Now

Because we retrofitted our mains hook up and it would have meant completely rearranging our electrical board in the van garage, we opted for a mobile mains hook up instead.

But if you’re including one in your electrical system from scratch getting a standard installation kit may make more sense.

Reverse Polarity

Reverse polarity is when the live and neutral cables are the opposite way round. And because UK sockets only cut the live (as oppose to both poles) it means your appliances would essentially be on instead of off and visa versa, which can be quite dangerous.

Because any mains power coming in only goes to our batteries and doesn’t directly power any additional 230V sockets in the van, we don’t need to worry about reverse polarity. But if you do choose to power any sockets direct from the grid and are planning on travelling outside of the UK in your campervan a reverse polarity tester will be important.

Lighting & Appliances

ComponentQuantityProduct Link
12V Dimmable LED Lights7View Now
12V Dimmable Bathroom Light1View Now
Reading Lights with USB Posts2View Now
Double USB Port2View Now
12V Fridge/Freezer1View Now
12V MaxAir Fan1View Now

Other appliances that we have connected to our 12V electrical system are; 10L Truma Ultrastore Water Heater, 5KW Diesel Air Heater, Thetford Cooker, LPG Fill Gauge, Shurflo Water Pump, Fresh & Waste Water Fill Sensor.

Fuses & Connectors

ComponentQuantityProduct Link
Battery Isolator Switch (100A)1View Now
50A Circuit Breaker2View Now
60A Circuit Breaker1View Now
Standard Blade Fuses (Assorted)1View Now
Battery Terminal Wing Nuts (+)3View Now
Battery Terminal Wing Nuts (-)3View Now
Cable Lugs (Assorted)1View Now
T Tap Connectors (Assorted)10’sView Now
Blade Terminals (Assorted)10’sView Now
Ring Terminals (Assorted)10’sView Now
Piggyback Terminals (Assorted)10’sView Now

Wiring & Accessories

ComponentQuantityProduct Link
12V Rocker Switch1View Now
230V Double Mains Socket1View Now
3 Core Flexible Mains Cable1View Now
Flexible PVC Battery Cable
(Red & Black)
N/AView Now
Various Thickness Single Core Cable (Red & Black)N/AView Now
Cable Grommets (Assorted)1View Now
Cable Clips (Assorted)1View Now
Cable Ties (Assorted)1View Now
Split Cable Tubing N/AView Now
Heat Shrink Tubing (Black)N/AView Now
Heat Shrink Tubing (Red)N/AView Now
Heat Resistant Fabric Tape1View Now

Sizing Your Van Conversion Electrics

Leisure Battery Bank Sizing

Create a spreadsheet with all the loads you expect to be running off your DIY camper electrical system.

You then need to calculate the amps for each and then estimate how many hours per day you’ll be using each item. And add these together to give your total estimated amp hour usage per day.

Amps = Watts / Volts
Amp hours = Amps x hours

We calculated that our maximum total estimated amp hour usage per day would be 140 Amp hours per day. That’s with everything running for the maximum time. Which just wouldn’t ever be the case. But using this estimate allows some leeway to be built in.

van conversion electrical system

If you’re not planning on using lithium batteries you will also need to double this as other battery types cannot be discharged below halfway without damaging them. We used AGM batteries so needed a minimum of a 280 Ah battery bank to support our system.

We installed 3 x 110Ah batteries, giving us a total of 330Ah in our leisure battery bank. Which means that we have more than one days energy storage in our batteries.

Solar Panel Power Sizing

Next up is to work out what amount of solar panel power you need to charge your battery bank. For this create another column in your spreadsheet. This time to work out the Watt hours.

Watts x Hours = Watt hours

Do the calculation for all of your loads, again using the same usage per day that you estimated when working out the Amp hours for each one. Then simply add them together to give you a total. Our total was 1750Wh.

Next you need to allow for how many hours of sunlight you anticipate having available and divide the total by that.

Watt hours / sunlight hours = solar panel wattage

For our campervan electrical system, we used 5 hours of sunlight to work out that we needed 350W of solar panel power to give our battery bank a full charge.

Solar Panels Van Conversion
Solar Panels Wired In Series

What we ended up going for was 3 x 150W solar panels. Again building in a little extra in case there isn’t so much sunlight. We were in rainy old England afterall.

Sizing Your Inverter

Okay first let’s tick off exactly what an inverter does because as mentioned previously, you only need one if you want to use regular 230V appliances in your camper conversion electrics.

And there are two different types of inverters; modified sine wave and pure sine wave. And there are pros and cons to each.

Modified or Pure Sine Wave?

The big benefit to modified sine wave inverters is that you can pick them up quite cheaply. On the down side they are however much less efficient, and just won’t work properly with some more modern or sensitive electronic appliances.

On the flip side pure sine wave inverters need way less battery power to convert electricity from 12V to 230V and will work with all electronic appliances. A decent one will however set you back several hundred pounds.

500W Victron Pure Sine Invertor

As already mentioned, we have a Pure Sine Wave Inverter. Our laptops are expensive bits of kit so we didn’t want to take any risks.

After you’ve worked out which type is best for you you need to work out what size inverter you need to match your DIY camper electrical system. And what you’re going to need in order to accurately work this out is a watt meter.

They’re not expensive, only a few quid, but what they do is accurately calculate the wattage of your appliances that you plan to plug into your inverter. Then add these together.

Something else to add to your DIY camper electrical system spreadsheet!

Of course you may not use them all simultaneously. But it’s best to work it out this way then you don’t have to worry about what you can and can’t use at the same time.

You will notice that some things like hair dryers and blenders have huge wattage. Not only will that draw more power out of your battery bank, the bigger the wattage of the inverter, the more expensive it is. So you may want to make some decisions there to keep sizings and costs down in your DIY camper electrical system.

Sizing Campervan Wiring & Fuses

Overheating of cables is a serious risk of electrical fire. This can occur by the cables not being appropriately sized or things like damaged cables or loose connections.

In standard operation, the cable alone should be of an adequate size to prevent overheating. But fuses are also used to protect the overheating of each circuit in your campervan electrical wiring when a fault occurs.

Therefore fuses are sized lower than the circuit they are being placed in to protect. The idea being that the fuse will trip, essentially breaking the circuit, before the cable overheats.

Fuse and cable ratings are both measured in Amps.

There are many different kinds of fuses, but the ones you will be most likely to use in van conversion electrics are standard blade fuses (1A – 40A) or midi link fuses (30A – 150A).

van conversion electrics circuit breakers

Alternatively you may also choose to use circuit breakers instead of inline midi link fuses in some places so that you can also use them as isolators.

Fuse Size Calculation

To calculate your required fuse size, you can use the following calculation:

Fuse rating = Max. Amp for appliance x 1.25

If the calculated amp rating is the same or very close to the amp rating of the fuse go up a size.

For example, our reading lights are 1.40 Amps each and we have 2 of them on the same circuit, making a total of 2.80 Amps. So 2.80 x 1.25 = 3.5 Amps. Therefore a 5 Amp fuse is required.

Note, fuses are only sized in specific ratings. E.g. for standard blade fuses 2, 3, 5, 7.5, 10, 15 etc. You should put all your calculations in your spreadsheet so you can refer back to them.

Some appliance manufacturers will also state recommended fuses, in which case you should use those.

Now for calculating the cable size. To get a starting point, you can use this equation:

Cable rating = Fuse size x 1.25

So using the same example as above, that would give a cable rating of 6.25 Amps (5 x 1.25) for the reading lights. Which equates to a 0.5mm2 (11A) cable size.

12 volt electrical system

Note cable sizes in the US are measured in AWG, not mm2 – but you can convert between if needed. There are plenty of comparison tables online.

But. And this is a big BUT, there’s something extra that needs to be taken into account when sizing cables for a campervan electrical system – voltage drop.

Voltage Drop Calculation

Voltage drop is caused by resistance (Ω/m) in cables, is multiplied by the cable length and is more significant in small voltage electrical systems.

The acceptable voltage drop for 12V circuits is 3-4% so we need to check the cable size using, yep you guessed it, another calculation.

Voltage drop = Current(Amps) x (cable length(m) x cable resistance(Ω/m))

You will find the cable resistance in the cable specifications. And the length you should use is the estimated whole length of the circuit i.e. both positive and negative cables.

Voltage drop = 6.25A x (6m x 0.0371Ω/m) = 1.391V

After that work out the percentage voltage drop using (1.391V/12V) x 100 = 11.5%

So in this instance we need to up the size of the cable size to account for the voltage drop because if we used there wouldn’t be enough current flowing and the lights would likely be flickering.

Going up to a 1.5mm2 cable with Amp rating of 21A and resistance of 0.0127Ω/m gives a voltage drop of 4%.

campervan wiring

If in any doubt, you should always go to the next size up because it can’t do any harm. It will also be simpler, if you have as fewer different sized cables for your loads as possible. For example we were able to use either 1.5mm2 or 2.5mm2 for all of our 12V loads.

But you still need to go through and do your calculations for each load to get to this point.

In addition be aware that different manufacturers can have different Amp and resistance ratings for the same cable thickness.

Battery to Battery Charging

Also known as B2B or DC-DC charging is a system that connects the vehicle starter battery with the leisure battery. Then while the vehicle is in operation, it pushes excess charge generated by the alternator into the leisure battery.

It prioritises the starter battery so it will disengage/engage automatically. Same as when the engine isn’t running so that leakage between the two doesn’t occur.

Battery to Battery Charger

If you have a smart alternator (i.e. generally Euro 5/6 compliant engines onwards) you have to use a battery to battery charger. However if you have an older vehicle, you can use a similar but much cheaper system called a split charge relay.

They both do the same thing.

As already mentioned we have a Sterling 12V/12V 60A Battery to Battery Charger. The B2B size you need is dependent on the size of your leisure battery bank and how quickly you want them to be charged.

The information is available in the product specifications.

Watch us installing our B2B Charger here:

Essential Campervan Wiring Tools

Here’s a quick run through of the essential diy campervan wiring tools that we had to purchase:

Solar Panel Wiring

If you have more than one, there’s a couple of different ways in which you can wire them up. In parallel or in series. Each has its own benefits.

Connecting electrical components together in a parallel means all positive cables are connected together and the negative cables are connected together. Consequently this adds the amperage together while the voltage stays the same.

Whereas wiring in series means connecting the positive and negative cables of each solar panel together. Which keeps the amperage the same but adds the voltage together.

Solar Panel Wiring Series or Parallel

But why does it matter and what’s the difference? Well because it affects how the solar panels perform.

If there is partial shade on one of your solar panels connected in series it will affect the output of the other solar panels. In parallel it doesn’t, the others will still work at maximum capacity.

However, because you need upwards of 14V in order for charge to be pushed into your batteries, solar panels wired in series will perform better on cloudy days. This is because they have a higher voltage range, so don’t need to be working anywhere near full capacity to be charging your batteries.

Being in the cloudy UK, we therefore wired our solar panels in series.

Wiring in parallel is also more complicated as it requires more equipment such as an MC4 connection branch, more fuses/breakers and an additional thicker length of cable.

Campervan Battery Setup

Opposingly, the three 12V batteries in our leisure battery bank are connected in parallel. They can only be wired this way as they need to be kept at 12V, not multiplied to 36V.

Also bear in mind that all your loads could potentially be drawing current through your battery bank. So ensure that the interconnecting cables are thick enough to support the total amperage of all of your loads.

Campervan Battery Setup

Something else to bear in mind if you are placing more than one leisure battery in your 12V campervan electrics is to connect your positive input/output and negative input/output at opposite ends so that the bank is discharged equally.

Take another look at our campervan diagram electrics if any of that is unclear.

Watch us wiring up our batteries & solar panels here:

Planning Wiring Routes

The vast majority of our campervan wiring is accessible. It runs under our bed and through our seating areas. We designed our system this way so that we could regularly visually inspect the cables for damage.

Planning Wiring Routes
wiring campervan electrics

Where they went through a space where they might rub such as from outside through the van floor or over a corner of wooden baton we put the cable inside some protective tubing.

Using The Vehicle Chassis

Rather than running negative cables back to the starter battery, vehicle manufacturers connect electrical components to the chassis. And then the starter battery to then chassis to complete the circuit. So the current naturally finds its way back to the negative terminal of the battery.

Subsequently this saves on the amount of cabling and is able to happen because the chassis is metal and an excellent conductor because it is sat on rubber tyres.

It is not possible to provide an earth to the ground via the chassis because of the insulating properties of rubber.

When installing a van conversion electrical system, it is best to keep that leisure system separate to the automotive electrics. So to clarify all of our electrical components are fully connected to our leisure battery bank with positive and negative cables.

Ask away in the comments if anything isn’t clear. But as already stated, do remember we are NOT qualified electricians, so any advice from us that you follow is at your own risk.

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Monday 31st of May 2021

As an electrician (note. Not an automotive one) I am throughly impressed with the level of detail here. Not many sparkies know all of the equations listed, and I am not undertaking the electrical side of my van build lightly! Great info and reference tool, thanks!

Sarah McAlister

Friday 4th of June 2021

Hi Mark, glad the info is proving helpful for you! It took me a long time to get my head around all the different aspects, so that's really great to hear. Appreciate you taking the time to comment :-)