Campervan electrics explained

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A major part of any camper van conversion is the electrical system. Design decisions will affect your van life so it’s vital to get the electric system right at the design stage.

Even if someone else is converting it, understanding the basics of campervan electrics will help you spec it out well.


Supply, voltage and capacity are the main differences between camper van and household electrical systems. Household supply is pretty much unlimited so you can use as much as you like.

In a camper van, you need to manage the supply and battery levels yourself. The voltage delivered into a house is much greater than in a camper.

At home, 240v of AC current allows a kettle of water to boil in a couple of minutes. A 12v DC kettle in your camper van will take as much as 20 minutes and a big drain on the batteries.

Managing the supply and usage of electricity becomes an integral part of van life.

This article explains everything you need to know about campervan electrics. It’ll help you design the right system for the van life you want. Feel free to drop us a line with any comments or questions!

We’ve drawn out our campervan wiring diagram here.

If you want to see our detailed electrical design, the electrical outlets we’ve installed and solar panel setup, that’s the post you need.

pin image for campervan electrics


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Overview of campervan electrics

This diagram explains campervan electrics in simple terms. The electrical system revolves around onboard leisure batteries.

Energy supplies charge and recharge the batteries which in turn, power all the camper van’s electrical appliances.

Camper van electrics - a simple diagram

The key to designing an appropriate electrical system is understanding the demand for energy, power consumption, how it’s stored and how to replenish it. 

To avoid disappointment on the road, these things need to be right at the design stage.

When living in a van, the electricity supply doesn’t have to be a let down if you design your electrical install well.


How much electric do you need in your camper van?

Close up of a lightbulb with bokeh light effects in the background

The first consideration in any campervan electrical design starts with understanding demand.

The whole calculation can seem quite complicated. So here I’ve tried to explain it in plain English with a working calculation to help explain it all. I hope you can follow along!

  1. Make a list of every appliance and gadget you carry in your camper van needing an electrical supply
  2. Identify the amps each appliance uses. Some appliances state the amps, others state the usage in watts. To calculate amps, divide the watts by volts. For example, an appliance is 6 watts, your batteries are 12 volts. 6 divided by 12 (watts divided by volts) is 0.5 amps
  3. Estimate the number of hours each day the appliance is in use
  4. Calculate the number of amps needed per day for each appliance
  5. Add together all amps needed per day. This gives you the total amp hours per day you expect to use
  6. Some days you will use more energy than others so add some contingency. We add 20% but you might want to add a little more or less for yourself. To add 20%, multiply total amp hours by 1.2

What capacity do you need in your camper van’s battery bank?

Batteries laid out in a triangle formation seen from above

Batteries aren’t 100% efficient so don’t deliver 100% of their amp hours. Even the cables running from the batteries to the sockets aren’t 100% efficient.

There’s a whole other science about batteries, how efficient they are and how they deteriorate over time.

Without going into the detail, we assume our deep cycle leisure batteries are 50% efficient and will remain at about that level for 3-4 years of continuous use.

We also know lead acid batteries are around 85% efficient if the charge/discharge currents aren’t too high.  Lithium ion batteries are even higher and nearly 100% efficient.

It’s not an accurate measure and I dare say many would dispute our assumption but it’s done us well over the past 15 years or so.

In our example, we expect to use 70 amp hours per day including contingency. If we installed only 70 amp hours in our battery bank, we’d only have 35 usable hours because we’ve assumed they’re only 50% efficient.

So, we need to double the amp hours when we buy batteries. In this example, we need 140 amp hours.

Now you know how much electricity you expect to use each day in your camper van and the battery bank capacity you need to meet demand.

The next step is understanding how you can recharge those batteries. First let’s take a look at camper van batteries in a little more detail and how to recharge them.


Campervan battery setup

Campervan electrics explained - charge batteries from engine

Vehicles have a 12v main starter battery fitted because they need energy to start the engine when you turn the ignition.

Main batteries give a surge of power (enough to start the engine) and recharged from the energy generated from the running engine as you drive.

If you turn your engine off but leave your lights on, you may end up with a flat battery and so unable to restart the engine.

Unless you only ever need an electrical supply in your camper van when your engine is running, you’re going to need a system a little more sophisticated than this.

Most camper vans have 12v deep cycle leisure batteries installed, designed for a gradual release of energy.

It’s a separate set up to the main battery so you can start your engine, regardless of the supply available or voltage in your leisure batteries.

Charging 12v batteries from your engine

The engine bay of a vehicle with the bonnet up

Using the engine to charge your leisure batteries is an efficient way to top up. Well, so long as you’re not running the engine just to charge your batteries. There are 2 ways you can install this:

Split charge relay on your main battery

A split charge relay fitted to your vehicle’s alternator output, prioritises the charge between the main and leisure batteries when the engine is running.

The main battery receives all the power until it’s fully charged. All power is then allocated to charging your leisure batteries.

In the event the leisure battery runs low, you could run your engine to top it up. The downside is you’ll need to carry out some emergency repairs to charge the batteries if the relay fails.

Separate alternator

Campervan electrics

To protect your main battery, you can fit a separate alternator to your engine as a dedicated charge to the leisure batteries.

The running engine charges both main and auxiliary batteries, leveraging otherwise redundant power. If the main battery alternator fails, you could rewire to the auxiliary alternator if you know what you’re doing.

Charging batteries from a shoreline hook up

Besides charging the auxiliary battery from the engine, you can also use a hook up facility.

By fitting a battery charger, you can convert the 240 volts AC mains supply to the 12 volts DC needed to charge the battery.

This allows you to plug the battery charger into the shore power and trickle charge the leisure batteries.

While you’re hooked up, you can pretty much use electricity as you would in a house so you don’t need to worry about your batteries too much.

For a detailed description of how to use shoreline hook up on campsites, take a look at this article from the UK’s Camping and Caravan Club. It gives loads of useful information on safety, cables you need and how to connect on site.

Solar power in your camper van

A man fitting solar panels to a Sprinter campervan conversion

Using camper solar power to charge van batteries is increasing in popularity, with advancements in technology and reducing prices fuelling its use.

You can fit rigid or flexible panels to your roof, or have portable panels, propping them up when you’re stationary.

After living in the van for over a 2 years now, I recommend rigid solar panels.

You need to fit a controller to convert the solar panel output into a consistent 12 volt DC charge. Then all you need is daylight.

I’ve fitted a 130 watt and 2x 95 watt monocrystalline solar panels to the roof of my Sprinter conversion and I can live off grid for 4 or 5 days in good weather and without driving. Not too shoddy! 

We could stay off grid for much longer if we switch off the fridge.

Wind power

A wind turbine against a cloudy grey sky

As with solar power, wind provides free energy and tapping into this is a great way to charge your camper van leisure batteries.

Installation is pretty much the same as with solar panels although you also need to consider mounting the wind turbine.

Don’t forget to make it demountable to avoid wrecking it as you travel. The added benefit is the wind turbine charges 24/7, assuming the wind is blowing of course!

Power from a generator for your camper van

Smoke billowing from an electricity cooling plant chimney

A portable generator also produces electricity. There is also an option of packing a generator to act like a campsite hook up. I’m not a fan because it’s too noisy when it’s running.

I’d also need to carry petrol and lifting heavy equipment in and out of the vehicle is a tad awkward.

Choosing how to charge your camper van’s leisure batteries is in part about your expected usage but also how you plan to live your van life.

If you only intend to stay at campsites and willing to pay a little extra for shoreline hook up, then you can get away with a low capacity battery bank and use as much electricity as you like while in situ.

If you’re hoping to live more off grid, don’t want to drive every day and have a few appliances needing electricity, you need to consider installing an alternator and solar power. In reality, most camper van owners will choose 2 or 3 charging methods.

To keep it simple, we’re first going to look at each method of charging our camper van batteries in turn.

Because we’ve assumed our batteries are only 50% efficient, we assume they are 50% empty in each of the calculations below.

To allow a simple comparison, we’ll also assume we recharge without using electricity at the same time.


How long do you need hook up to recharge your batteries?

To recharge your camper van battery bank from a hook up, you need a battery charger fitted to convert the 240v AC supply to a 12v DC supply.

The size of the battery charger determines hook up time needed.

Let’s assume we have a 20 amp hour battery charger unit.

Camper van electrics explained - hook up calculation

In our working example, we have a battery bank of 140 amp hours at 50% empty. So we need to recharge 70 amp hours.

With a 20 Ah battery charger fitted, in theory we need to hook up for 3.5 hours to recharge.

In reality even charging batteries isn’t 100% efficient so we need to make an allowance.

Again, we assume 50% efficiency so to recharge our 140Ah batteries from hook up, we’d reckon on around 7 hours.


How long do you need to run your engine (or drive) to recharge your batteries?

The calculation is like the hook up calculation above only you replace the battery charger amp hours with the amount of amps the alternator delivers to your battery bank.

You need to check the rating of your alternator to identify how many amps it produces.

Ours produces 100 Ah when the engine is running over 1200rpm (so when we’re driving). At idle it produces 50 Ah.

Camper van electrics explained - engine calculation

In our working example, we have a battery bank of 140 amp hours at 50% empty, so we need to re charge 70 amp hours.

With an alternator rated at 100 Ah, in theory we need to drive for 42 minutes to recharge our battery bank.

In reality even charging batteries from the engine isn’t 100% efficient so we need to make an allowance in our calculation.

Again, we assume 50% efficiency so to recharge our 140 Ah batteries from the engine with a 100Ah alternator, we’d drive for about 90 minutes.


How much sun do you need to recharge your batteries?

A beam of sunlight shining through a forest onto a road

So this calculation is a little more speculative because the energy from daylight is inconsistent. The sun isn’t in the best position to deliver energy to the solar panels all day.

Shade and cloud will interfere with the level of energy delivered too. So to try to keep it simple, let’s assume we get 8 hours of full sun daylight per day.

Now we’ll calculate how many amps a 100w solar panel could generate.

For each full hour of full sun, a 100w panel can generate 100 watts of energy. Our battery is a 12v battery.

To calculate amps, we divide watts by volts. So our 100w solar panel could generate 100 watts/12 volts = 8.3 amps per hour.

In our working example, we need to generate 70 amps to recharge our camper van batteries and at 8.3 amps per hour, we need about 8.5 hours of full sun on one 100w solar panel.

If we have 4 solar panels each of 100w on the roof of our Sprinter so in theory, with full sun for a little over 2 hours, we’d recharge our 140 amp hour batteries.

You can guess by now, the reality is somewhat different. Because of inefficiency of the panels and charger, the battery doesn’t receive all the amps delivered.

We work on an assumption of 20% efficiency from the solar panels so we need about 10 hours of full sun to recharge.


The reality of how much energy we generate in our camper van

Camper van electrics explained - monitor batteries

We don’t use hook up often so rely on the solar panels and alternator to generate enough energy.

In the middle of somewhere like the Sahara desert, we don’t worry too much about our batteries. We got plenty of sun on our 400w solar panels to keep our batteries topped up.

And even now with the 130w mono crystalline solar panel, we manage well.

On long drives, it’s easy to recharge our batteries enough to get us through the day.

Most of the time we don’t drive for much longer than 2 or 3 hours and the weather isn’t always kind. Over the years we’ve got used to monitoring and obsessing over our battery levels and usage.

We instinctively know when we have enough energy to power the inverter.

We celebrate like hippies at Stonehenge when our controller show us getting loads of energy into the solar panels.

And when we do use a hook up, we go overboard charging every device and gadget we can find! It’s all part of life as an overlander.


Top tips for managing your campervan electrics

  • Minimise your energy demand by choosing efficient appliances. Always compare the Ah ratings of alternative products before you buy. Some manufacturers display amp hours (Ah); others show watts. Convert watts to Ah by dividing watts by 12 volts.
  • Where possible, choose 12v appliances because they’re more efficient than 240v alternatives.
  • Remember you need an inverter to use 240v appliances in your camper. The inverter also uses energy so make sure to include this in your usage calculations.
  • Some cheaper versions of inverters provide a square wave as opposed to a nice, clean sine wave. Some delicate electronics such as TVs, do not work well on square waves. Ensure you invest in the right product to meet your needs.
  • Where a 12v alternative appliance is available, do a quick calculation to work out which one is more efficient. Don’t forget to include the use of the inverter for the 240v appliance.
  • When you open an upright fridge, more cold air is lost than when you open a box one (because cold air sinks). More energy is used to bring the upright fridges temperature back down when you close the door. Box fridges tend to have lower overall energy consumption.
  • Invest in a good power management system to control and monitor your campervan electrical system.
  • Use high quality marine grade components because their specification is built to withstand tough environments.
  • Use the appropriate wire gauge to give you the maximum electrical efficiency, safety and practicality. Seek advice on the wire gauge to use based on the currents and voltages you expect your electrical setup to use.
  • Isolate every component through fuses or isolating switches to protect the battery from voltage and current spikes. A battery isolator is an essential safety component for your van’s electrical setup.
  • If you lack electrical skills or confidence, this is an area where it pays to get professional assistance with the installation. After all, you don’t want an incorrectly fitted system to cause a fire!

When it comes to campervan electrics, there’s one simple rule: you must put in more than you take out. The best advice for any overland vehicle is to keep the electrics simple and your output needs to a minimum.


Materials you need to install your campervan electrics

Here’s an idea of some of the big ticket items needed to install the electrical system in your camper van. We’ll provide a detailed list of materials, costs and tools in our how to guides coming soon.

  1. Solar panels
  2. Inverter
  3. Deep cycle leisure batteries

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8 thoughts on “Campervan electrics explained”

  1. I have had recently installed two lithium 100ah batteries and upgraded all the wires also installed a battery monitor system (victron)

    I’m trying to figure out why my battery monitor tells me in a day I’ve used around 20ah but my battery charge level at the end of a day of use is around 40% left

    Why do 200ah batteries use 60% of there energy but only show 20 ah of discharge?

    • Hi Mitchell, I’m not sure exactly but I’d start by checking the monitor is set for the correct battery type, it’s monitoring all the load and all connections are tight.
      Other than that, it’s pretty for us difficult to fault find remotely. I hope that helps.
      Angela & Graham

  2. Hi,
    I am probably going to ask a tonne of stupid questions. But I am struggling on figuring out what type of battery would be best and why as the calculations confuse me. I have given it a go but I’m not the best at working it out.
    Myself and my partner are converting our van at the moment and the big thing we’re stuck on is the battery. We figured that we would most likely have
    2 phones
    Laptop charger
    Blender
    Fridge/Freezer
    2 water heaters
    Normal heater
    AC?
    Microwave
    Lighting
    Electrical outlets
    Stove

    We don’t know all of the Ah for these appliances and can’t figure out what the calculations would be as we have not bought all of them yet.
    We also wondered whether it would be worth buying an inverter and converting it to AC power as opposed to DC power, as it would be easier for things like charging phones etc.
    Please get back to me :)
    Thank you so much.
    Lauren

    • Hi Lauren

      Batteries supply DC power i.e 12v.

      Phones, laptop chargers & lighting are easy to run on 12v.

      Fridges and cookers can all be purchased to run on 12v too – or bottled gas.

      Heating & water heaters run on gas, diesel or some with a 12v supply.

      The battery bank needs to be recharged with energy, be that from the sun, charging from your engine, external generators or via a battery charger hooked up to the mains.

      To run your AC appliances like the microwave, Air Con and blender, you’d need a large inverter which alone is an inefficient use of your batteries. Those appliances running will then quickly drain said batteries. It’s probably not practical to have a battery bank big enough in a van to run all those AC appliances.

      If you plan to be hooked up to mains power more often than not, then this wouldn’t be as much of a problem. If you only use them when hooked up. This way you don’t use the energy from your batteries.

      In terms of the calculation, even without having purchased your DC appliances, you can still calculate your consumption needs with a few assumptions.

      For each appliance, pick a product you might purchase and check the Ah. Use this as the basis of your calculation. It may not be wholly accurate but it’ll give you a fair idea.

      To start calculating your needs for the AC appliances is too complicated for me. You’d need to understand the base load of the inverter, then its consumption profile based on the appliances hooked up to it. And that was complicated for me to write let alone work out :-0

      My advice is to reduce your dependency on AC appliances.

      I hope this helps!

  3. Can I run the ninternal electrics eg fridge sockets and water supply to my sink without an electrical hook up

    • Hi Gordon. Yes you can. You run them from the batteries as long as the fridge is 12v. You should install some leisure batteries to save the main battery from draining. So you need a way to charge those batteries – solar or a smart relay will do the job.

  4. Pingback: Little Book of Camper Van | Workshop Manuals
  5. in the battery charging equation from running engine,

    battery bank capacity x battery efficiency
    ——————————————
    Alternator Ah

    the 50% efficiency works out at 30.

    Where does the 30 come from? Is it the usable hours (working example giving 35 hours) rounded down?

    This is the only bit i don’t understand from an otherwise very helpful and well written guide, thankyou in advance!

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