Plan your campervan electrics — from wiring diagram to parts list
A free tool for laying out the 12 volt system in your campervan or motorhome: connect battery, solar, DC-DC charger and loads, get cable cross-sections and fuse sizes calculated for you, and catch mistakes before they are bolted into the vehicle.
Start planning Just size a cable
Why the electrics deserve a plan first
In a self-build, every shortcut gets paid for exactly once — but thoroughly. The three mistakes that come up most often:
Undersized cable. At 12 volts the same power draws roughly twenty times the current it would at 230 volts. A 2000 W inverter pulls close to 175 amps. A cable too thin for that gets warm — in the worst case warm enough for the insulation to give up. Voltage drop along the run adds to it: whatever is lost on the way never reaches the load, it heats the cable instead.
Wrongly sized fuses. A fuse does not protect the appliance, it protects the cable. So it has to match the conductor size, not the consumption. A 100 A fuse in front of a 6 mm² cable is about as useful as no fuse at all.
Battery and charging gear that do not match. LiFePO₄ needs different charge voltages than AGM or gel, and not every controller supports every chemistry. Mixing them costs capacity at best and the battery at worst.
What the planner does for you
- Click the system together — battery in the middle, sources on the left (solar, alternator, shore power), loads on the right. Components can be dragged to a different branch at any time.
- Continuous plausibility checks — it flags mismatched voltages, wrongly sized fuses, a switch that would trip before the fuse can protect the circuit, or a battery chemistry that needs deep-discharge protection.
- Energy balance — harvest against consumption, with operating hours per device, giving you the number of days the system runs off-grid.
- Cable cross-sections — for every connection, based on length, current and voltage.
- Parts list with price estimate — as a shopping list you can print.
Three steps to a finished plan
- Connect Pick a template or start from scratch, add components from the database and wire them up.
- Calculate Immediate feedback on capacity, current draw, cross-sections and potential problems.
- Build Export the parts list and diagram, and start the build with a plan that has been checked.
Template: 100 W solar with cool box Template: 540 W build
Common questions
How much solar do I need?
That depends on consumption, not on roof area. Add up what your devices draw per day — compressor fridge, lighting, water pump, charging phone and laptop — and allow around 20 per cent headroom. Battery size and solar output follow from that number, in exactly that order. The planner works the same way round.
Is solar alone enough?
In summer usually, in winter rarely. Between December and February the same array delivers a fraction of its summer yield in northern latitudes. Anyone wanting year-round autonomy normally combines solar with a DC-DC charger on the alternator.
Do I need a DC-DC charger?
With a LiFePO₄ battery, essentially always. The alternator on its own does not reliably reach the required charge voltage, and modern vehicles actively regulate system voltage down. A B2B charger decouples starter and leisure battery and charges with the profile the chemistry needs.
Can I do this myself?
The 12 volt side can be installed by careful self-builders. The 230 V / mains side is a different matter and is subject to national regulation — in Germany, shore power installations must be built and signed off by a qualified electrician under DIN VDE 0100-721. Check the rules that apply where your vehicle is registered.
Next: the cable calculator
If you only need to size a single run, the cable calculator is quicker: enter length, current and voltage, read off the cross-section together with voltage drop and power loss. The derivation of the formula and a table of typical campervan cases are on the cable cross-section page.