Camper van wiring plan: from power budget to wiring diagram

The first decision is your system voltage. Most camper vans use 12V because it's simple and nearly all camper appliances run on 12V. But for larger systems (above 200Ah), 24V can be more efficient: cables can be thinner and you lose less power.

12V is the right choice if you're building a standard camper with lighting, fridge, USB charging and a water pump. 24V becomes interesting when you're planning a large system with induction cooktop, AC or heavy electrical consumers.

Also choose your battery type: lithium (LiFePO4) is lighter, lasts longer and delivers more usable capacity than AGM (absorbent glass mat, a sealed lead battery) or gel. The higher purchase price pays for itself in lifespan.

Make a list of every electrical appliance in your camper. Note the power (watts) and the estimated use per day (hours) for each. Multiply those for the daily consumption in watt hours (Wh).

Example: LED lighting (10W x 5 hours = 50Wh), compressor fridge (18W on average x 12 hours of running = 216Wh), water pump (60W x 0.5 hours = 30Wh), phone charging (10W x 3 hours = 30Wh). Total: around 325Wh a day.

Watch the fridge. The label often says 45W, and it does draw that while the compressor runs. But it does not run continuously; measured across 24 hours it comes to around 18W. Work with the peak and you size your whole battery too large.

Add 20% to your total for cable losses, inverter losses and unforeseen use. That gives you a safe margin.

Every cable in your camper van must be thick enough for the current flowing through it. At 12V the current is much higher than you might expect: a 100W device draws over 8A at 12V.

The correct wire gauge depends on three factors: the current (amps), the cable length (one way) and the maximum allowable voltage drop (3% is the default the cable calculator works with, 1-2% for sensitive equipment). The longer the cable and the more current, the thicker the cable must be.

Every cable needs a fuse, as close to the battery (positive terminal) as possible. The fuse protects the cable, not the device. Choose a fuse that matches the maximum current rating of the cable, not the consumption of the device.

To charge your batteries you need one or more charging sources. The most common combination is solar panels plus a B2B (battery to battery, a charger between the starter and house battery) charger (charges while driving via the alternator).

For solar panels: divide your daily use by the yield per watt-peak. Our tools work with the peak sun hours that belong to your latitude. At 52 degrees north, roughly the Netherlands, that is 5.4 sun hours in July, 4 in April, 2 in October and 0.8 in December. At 80 percent system efficiency each watt-peak then gives 4.3 Wh in July, 3.2 Wh in April, 1.6 Wh in October and 0.6 Wh in December. So at 325Wh a day you need around 75Wp in July, 102Wp in April and 203Wp in October. December works out at 508Wp, and that number is exactly why almost nobody gets through a northern winter on solar alone: count on driving or shore power there.

An MPPT (maximum power point tracking, the technique that gets the most out of a panel) charge controller extracts 20-30% more energy from your panels than a PWM (pulse width modulation, the simple type of charge controller) controller. For panels above 100Wp, MPPT is almost always the better choice.

Also consider shore power (230V/120V charger) for when you're at a campsite. This gives you three independent charging sources.

With your consumption, cables and charging sources determined, you can choose your components:

Battery: choose a capacity that covers at least 2 days of use. At 325Wh a day that is 650Wh. You use 80 percent of a lithium battery, so you need 813Wh nominal: a 65Ah battery at 12.8V (832Wh) fits that exactly. With AGM or lead you use only 50 percent, so there you need 1300Wh, which is a good 100Ah.

Inverter: only needed if you use 230V/120V appliances. Choose a pure sine wave inverter and size it for the heaviest device you want to run simultaneously.

Fuse box: a central distribution point for all your circuits. Use a busbar for positive and one for negative, with individual fuses per circuit.

Switches: a main switch at the battery and switches per circuit for convenience and safety.

Before you cut a single wire, draw a complete wiring diagram. This diagram shows all components, cables, fuses and connections. It's your blueprint for the installation and indispensable when troubleshooting later.

A good diagram includes: the battery with main fuse, the distribution point (busbar/fuse box), all circuits with wire gauge and fuse rating, the charging sources (solar panel, B2B, shore power) and optionally an inverter.

Keep your diagram in a safe place inside the camper van. When you want to add something later or trace a fault, it's worth its weight in gold.

A diagram on paper only becomes an installation once the cables are in, and that order is unforgiving: everything that disappears behind a wall or under a floor has to go in before the panelling.

So run all the cables first, including those for equipment you will not buy until next year. A spare cable laid in now costs a few euros; the same cable afterwards costs a day of taking panelling apart.

What belongs with that:

• Cables through metal holes fitted with a grommet or a piece of hose, because a sharp edge cuts through insulation over time
• Every cable secured every thirty to fifty centimetres so it cannot vibrate and chafe
• Generous bends and no tight corners, and never a cable pulled tight over an edge
• Positive and negative running together, because a loop between the two wires picks up interference

Label every cable at both ends before you close it in. Two years from now, with a fault and a torch in your hand, that is the difference between ten minutes and half a day.

The last step before the first current is a check you do without power. A fault you find now is a correction; the same fault after connecting is smoke.

Work through these points:

• Use the continuity function on your multimeter to confirm there is no connection anywhere between positive and negative
• Check at every appliance that positive and negative are not swapped; an inverter or charge controller rarely survives that
• Verify that each fuse holder contains the fuse from your diagram, not the largest one that happened to fit
• Tug on every cable lug; anything that comes loose was not crimped properly
• Check that earth connections sit on bare metal rather than on paint or rust

Then connect the battery last, with the main switch off and the fuses in place. Switch the circuits on one at a time and check at each one whether anything gets warm.

Finally, photograph your installation before the panels go on, and keep your diagram. That is for yourself when there is a fault, and for a buyer or an inspector it is the evidence that thought went into it.