Guide
Campervan electrical system: what it costs and how to size it
Updated
Almost every conversion budget is broken by electrics. Not because components are expensive on their own, but because each appliance you add pushes three other things up with it.
Start with an energy budget, not a shopping list
The single most useful hour you can spend on a van build is writing down every electrical item, what it draws, and how many hours a day you will run it. That gives you a daily amp-hour figure. Everything else, battery capacity, solar array, charging strategy, inverter rating, follows from that number. Choosing components first and hoping is how people end up with a bank that will not last a weekend, or a bank three times bigger than they need.
Why it compounds
- Add a compressor fridge
- It runs day and night, so the daily draw rises permanently. The battery grows, and the charging has to keep up in poor weather.
- Add an inverter and a mains appliance
- Peak current rises sharply, which changes battery chemistry choice, cable sizes, fusing and often the battery bank size too.
- Add winter use
- Shorter days mean solar contributes far less, so alternator charging or hookup has to do the work. That means a DC-DC charger and heavier cabling from the starter battery.
- Add a diesel heater
- Modest draw, but it runs at night when solar contributes nothing, which is exactly when reserve capacity matters.
The decisions that move the price
- Battery chemistry and capacity. Lithium costs more up front and buys usable capacity, weight and cycle life. Lead acid is cheaper per nominal amp-hour and heavier for the usable capacity you actually get. Neither is wrong; they suit different budgets and uses.
- Solar array size, and how much roof you are willing to give up, bearing in mind a pop-top or roof vents compete for the same space.
- Charging from the engine. A DC-DC charger and the cable run from the starter battery are a significant install job, and on many modern vehicles they are the only safe way to charge while driving.
- Inverter rating. Be ruthless here. Sizing an inverter for a kettle you will use twice a year is an expensive habit.
- Mains hookup and RCD protection, if you want to use campsite electricity.
- Installation quality: cable sizing, fusing, terminations, strain relief and a clear schematic. This is where a professional install earns its money and where self-builds most often go wrong.
What to ask any installer for
- A schematic of the system as installed, not a verbal description.
- The battery capacity and chemistry, the solar wattage, the inverter continuous and peak ratings, and the DC-DC charger rating.
- Cable sizes and fuse ratings for each circuit, and where the isolators are.
- Confirmation that the mains side, if fitted, has appropriate protection and has been tested, with documentation.
- A handover walkthrough: what to do when something trips, where the fuses are, how to check the state of charge.
- What the system will realistically deliver in December, not in June.
This page explains how to size and specify a system, not how to install one. Twelve volt work is unforgiving of poor terminations and undersized cable, and mains and LPG work should be done by people qualified for leisure vehicle installations. Keep every certificate and schematic you are given.