Camper van electrics explained

A major part of any camper van build 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 camper van electrics will help you spec it out well.

Supply, voltage and capacity are the main differences between camper van and household electrics. 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 electricty becomes an integral part of van life.

This article explains everything you need to know about camper van 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!

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Overview of camper van electrics

This diagram explains camper van 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 diagramThe key to designing an appropriate electrical system is understanding the demand for energy, 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.

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How much electric do you use in your camper van?

The first consideration in any camper van 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 per hour each appliance uses. Some appliances state the amps per hour on the label as Ah. Others state the usage in watts. To calculate Ah, 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 Ah

3: Estimate the number of hours each day the appliance is in use

4: Calculate the number of amp hours needed per day for each appliance.

5: Add together all amp hours 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

Follow the example calculation in the video below:

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

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. 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.

Also read: Camper van water systems explained

Camper van batteries

Vehicles have a 12v main battery fitted because it needs 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 in your leisure batteries.

Charging 12v batteries from your engine

Campervan electrics explained - charge batteries from engine

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 relay on your main battery
By fitting a split relay to your vehicle’s alternator output, it prioritises the between the main and leisure batteries when the engine is running. The main battery receives all the power until it’s 100% 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

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 plug the battery charger into the shore power and trickle charge your 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.

Solar power in your camper van

Using solar power to charge camper 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. 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.

Wind power

Camper van electrics explained - charge batteries by wind power

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

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 mintes.

How much sun do you need to recharge your batteries?

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. We happen to 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 40% efficiency from the solar panels so we need about 5 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 get plenty of sun on our 400w solar panels to keep our batteries topped up. 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 u 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 camper van 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 camper van electrical system.
  • Use high quality marine grade components because their specification is built to withstand tough environments.
  • Isolate every component through fuses or isolating switches to protect the battery from voltage and current spikes.
  • 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 camper van 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 camper van 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.





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All you need to know about camper van electrics in one easy to read post. Whether your doing a diy conversion or handing your van over to a builder, read this to spec out your wiring needs correctly. Read the full article here: #CamperVanConversion #VanLife #SprinterConversion

All you need to know about camper van electrics in one easy to read post. Whether your doing a diy conversion or handing your van over to a builder, read this to spec out your wiring needs correctly. Read the full article here: #CamperVanConversion #VanLife #SprinterConversion

All you need to know about camper van electrics in one easy to read post. Whether your doing a diy conversion or handing your van over to a builder, read this to spec out your wiring needs correctly. Read the full article here: #CamperVanConversion #VanLife #SprinterConversion

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