Wiring a van electrical system
Most write-ups start at the solar panel. That is the wrong end. The panel is the last decision, not the first, and building in the usual order is why so many conversions get rewired twice.
Some links here are affiliate links. If you buy through one we may earn a commission at no additional cost to you.
Start with the load list, not the kit list
Every downstream component is determined by one number: watt-hours per day. Until you have it, every product comparison you read is meaningless, because you cannot tell whether the thing being reviewed is too small, too big or irrelevant to you.
Sit down with a notebook and list what you will run, its wattage, and the hours it will genuinely operate. Be honest about the fridge — it cycles rather than running constantly, but in summer it can be on for eight hours out of twenty-four.
Do this first. The battery bank calculator turns that list into an amp-hour figure, and carries it through to the array and inverter pages.
Choose system voltage before you buy anything
This is the decision that is genuinely painful to reverse, because it invalidates your batteries, inverter, controller and often your cable.
| Voltage | Suits | Trade-off |
|---|---|---|
| 12V | Under about 2 kWh/day. Cheapest accessories, huge parts ecosystem. | High current. Cable gets thick and expensive fast. |
| 24V | 2–4 kWh/day. Halves the current for the same power. | Fewer bolt-on 24V accessories; you will need converters. |
| 48V | Larger builds, air conditioning, induction cooking. | Overkill for a weekend van; component cost steps up. |
The practical rule: if your inverter would pull more than roughly 200 amps on the DC side, step the voltage up. The cable saving alone often pays for the difference.
The build order that avoids rework
- Bank and its protection. Battery, main fuse within a short distance of the positive terminal, and the busbars everything else will land on.
- Charge sources. Alternator charging (a DC-DC charger, not a plain relay, if you are running lithium), then shore power, then solar. Solar last because it is the one you can add to later without touching anything else.
- Inverter. Mounted close to the bank on short, heavy cable.
- DC distribution. Fuse block, then the circuits for lights, fans, pump, sockets.
- Monitoring. A shunt-based monitor. Fit it at the start rather than the end — you cannot manage a bank you cannot see.
Protection is not optional, and it protects the cable
The most common misunderstanding in van builds: a fuse is not there to protect the appliance. It is there to stop the cable becoming a heating element when something shorts. That means the fuse rating follows the cable's ampacity, not the device's draw. DC cable and fuse sizing works it through with numbers.
Every conductor leaving the battery positive needs protection as close to the terminal as practical. A lithium bank can deliver enormous fault current — far more than lead acid — and an unfused run in a vehicle that vibrates for a living is a fire waiting for a chafed sleeve.
Where people overspend
- Inverter capacity they use twice a year. A 3000W unit idles away real power every day so that you can occasionally boil a kettle. Consider whether gas covers cooking.
- Panels instead of alternator charging. If you drive regularly, a DC-DC charger delivers more reliable amp-hours than another 200W on the roof, and it works in January.
- Battery capacity instead of a monitor. Most people who think they need a bigger bank are actually running a phantom load they have never measured.
What to check before you close the walls
- Every crimp tested by pulling on it, hard.
- Grommets or glands anywhere a cable passes through metal.
- Cable secured every 300 mm or so, so vibration cannot saw it against an edge.
- The main fuse actually accessible without dismantling furniture.
- A wiring diagram, photographed, stored somewhere that is not the van.
Next. Run your figures through the battery calculator, then check the winter number on the array calculator. If the winter figure is more than double the annual one, plan for a second charge source now rather than discovering it in December.
This guide gives planning estimates. Vehicle electrical installations should be checked against the regulations that apply where you are, and by someone qualified if you are not.