How to choose a suitable inverter for your camper van

An inverter is a device that transforms DC (Direct Current) from your battery bank into AC (Alternating Current), the same type of power you have at home. In Europe this means 230V at 50Hz, in North America 120V at 60Hz.

Not every camper van needs an inverter. If you only charge phones, run LED lights and use a 12V compressor fridge, you can get by entirely on 12V DC. But as soon as you want to use household devices like a laptop charger, an electric kettle, a coffee machine, a hair dryer or power tools, you need AC power.

The inverter sits between your battery bank and a 230V outlet or distribution panel. It draws DC current from the batteries and outputs AC power. Keep in mind that this conversion is not 100% efficient. A typical inverter loses 10-15% of the energy as heat during conversion. That means a device drawing 100W from the AC side actually consumes about 115W from your batteries.

This efficiency loss is important when sizing your battery bank and solar panels. Always factor in inverter losses when calculating your total daily power consumption.

Inverters come in two main types: pure sine wave (PSW) and modified sine wave (MSW). The difference lies in the shape of the AC waveform they produce.

A pure sine wave inverter produces a smooth, continuous wave identical to what the electricity grid delivers. All devices work correctly on a pure sine wave. This includes sensitive electronics like laptops, medical devices (CPAP machines), microwave ovens, variable-speed motors and audio equipment.

A modified sine wave inverter produces a stepped, blocky approximation of a sine wave. It is cheaper, but many devices do not run well on it. Motors run hotter and noisier, laptop chargers may overheat, LED dimmers buzz, and some devices refuse to start altogether. Clocks and timers may run inaccurately.

For a camper van, a pure sine wave inverter is almost always the right choice. The price difference has shrunk considerably in recent years, and the compatibility with all devices gives you peace of mind. A good-quality 1000W PSW inverter costs between 150 and 300 euros.

Only consider a modified sine wave inverter if you exclusively power simple resistive loads like incandescent bulbs or basic heaters, and you are on a very tight budget.

Every inverter has two power ratings: continuous (or rated) power and surge (or peak) power. Continuous power is what the inverter can deliver indefinitely. Surge power is what it can handle for a few seconds when a device starts up.

To size your inverter, list all the AC devices you might run at the same time. Add up their wattage. That total is your minimum continuous power requirement. Then check if any of those devices have high startup currents: compressors, power tools and devices with electric motors often draw 2 to 5 times their rated wattage for the first second.

Example: you want to run a laptop charger (65W), a phone charger (20W) and a blender (300W) simultaneously. That is 385W continuous. The blender motor may surge to 900W on startup. So you need an inverter with at least 400W continuous and 900W surge, a 600W unit with 1200W surge would give you comfortable headroom.

A common rule of thumb is to size your inverter at 125-150% of your maximum expected simultaneous load. This gives you margin for efficiency losses and prevents the inverter from constantly running at full capacity, which shortens its lifespan.

Also consider the DC current draw. A 2000W inverter on a 12V system pulls up to 180A from the battery. That requires very heavy cables (50 mm² or more) and a suitable fuse. Think about whether you truly need that much power.

Appliances with a motor or a compressor briefly draw far more than their rated power when they switch on. A fridge compressor, a pump, a drill or an air conditioner can ask three to six times as much for half a second.

That is why every inverter quotes two figures: continuous power and peak power. The continuous figure is what it can hold for hours, the peak figure what it delivers for a few seconds. On most inverters the peak is roughly double the continuous rating.

What that means for your choice: add up your continuous loads for the first figure, and look at the heaviest inrush for the second. A 2,000 watt kettle has no inrush and therefore needs 2,000 watts continuously. A small 300 watt compressor can peak at 1,200 watts while asking little continuously.

And remember the battery has to supply that too. A 2,000 watt peak at 12 volts is nearly 200 amps from the battery; a small lead battery sags so far under that load that the inverter cuts out on undervoltage while on paper nothing is wrong.

An inverter that is switched on with nothing to do still uses power. That is idle draw or no-load consumption, and on a 2,000 watt inverter it often sits between 8 and 20 watts.

Over a day that is 200 to 480 watt hours, which in many campers is more than the fridge. It is also the item people overlook longest, because nothing visible happens: a light is on, that is all.

Three ways to limit it. Switch the inverter off when you are not using it, which is simplest and yields most. Use its power save mode if it has one: the inverter then wakes itself a few times a minute and only comes fully on when it sees a load. Or put it on a switch by the door, so switching off becomes as automatic as turning off the light.

So when choosing an inverter, look beyond power and efficiency to no-load consumption. Two inverters of the same rating can differ by a factor of two there, and over a year of travel that is half a battery.

Proper installation of your inverter is critical for safety and performance. The inverter should be mounted as close to the battery bank as possible to minimise cable length and voltage drop on the DC side. Keep cables under 1.5 metres if you can.

Use appropriately sized DC cables. Guidelines for a 12V system with runs under 1.5 metres, based on the current the inverter draws at full power:

• 500W inverter: around 50 A, minimum 25 mm² cable
• 1000W inverter: around 100 A, minimum 35 mm² cable
• 2000W inverter: around 200 A, minimum 95 mm² cable
• 3000W inverter: around 295 A, minimum 150 mm² cable

Those cross-sections climb fast because current climbs fast at 12V. From roughly 2000W upwards a 24V system is the sensible choice: at the same power the current halves and you get away with half the copper. Check your own case with the cable calculator, which uses the same capacity table as this guideline. Always install a fuse or circuit breaker on the positive cable, rated for the cable's maximum capacity, not the inverter's power rating.

Ventilation is essential. Inverters generate heat, especially under load. Mount the unit in a well-ventilated space, not inside a sealed cabinet. Many inverters have built-in fans, but they still need airflow around them. Keep at least 10 cm of clearance on all sides.

On the AC (output) side, use standard household wiring practices. Install an RCD (Residual Current Device, also called GFCI in North America) to protect against electric shock. Wire the AC output to a small consumer unit or distribution board with individual MCBs (Miniature Circuit Breakers) for each circuit.

Finally, install a remote on/off switch if your inverter supports it. Inverters draw a small amount of standby power (5-20W) even when nothing is connected. Turning it off when not in use saves your battery capacity.

An inverter shuts itself down when something is off, and knowing those limits saves searching when it happens.

The four you meet most often:

• Undervoltage: the battery is empty or the cable is too thin, so voltage sags under load
• Overload: demand exceeds what the inverter can supply, often from an inrush current
• Temperature: insufficient cooling, usually because the inverter sits in a closed locker or hard against a wall
• Overvoltage: a charger going too high, or a battery management system that does not switch along

The first two almost always point to wrong sizing somewhere in the chain rather than a broken inverter. Measure battery voltage at the inverter terminals while the load runs; if it is clearly lower than at the battery itself, the problem is in the cable or the connections.

Give the inverter air: a few centimetres clear on all sides and nothing on top. Most inverters cool with a fan drawing from bottom to top.