CAMPER
ELECTRICAL BASICS.
A plain-English introduction to leisure batteries, alternator charging, solar, shore power, inverters and protection. It explains how the pieces fit together without pretending a web page makes somebody qualified to redesign a 230V installation.
What a Camper Electrical System Does
A typical camper system stores energy in a leisure battery, receives energy from one or more charging sources and distributes it safely to the equipment you use.
- Battery: stores energy.
- Alternator/DC-DC charger: charges while driving.
- Solar panel + MPPT controller: charges from sunlight.
- Shore-power charger: charges when plugged into mains.
- 12V distribution: feeds lights, pumps, USB outlets and other DC loads.
- Inverter: turns battery DC into 230V AC where required.
- Fuses/breakers/isolation: protect wiring and equipment.
- Battery monitor: helps show what is going in and out.
The Leisure-Battery Side
Most camper equipment can run directly from the low-voltage battery system: lighting, water pumps, USB charging, compressor fridges and control equipment. Keeping suitable loads on DC avoids unnecessary inverter losses.
The leisure system should be separated and protected so normal camping use does not leave the starter battery unable to start the van.
Choosing a Leisure Battery
Lead-acid and lithium batteries behave differently in usable capacity, charging requirements, weight and cost. Lithium systems also rely on a suitable battery-management system and compatible charging equipment.
- Size the battery around daily energy use, charging opportunities and desired reserve.
- Check that every charger is compatible with the battery chemistry.
- Do not assume replacing lead-acid with lithium is simply a case of fitting different terminals.
- Mount and protect batteries appropriately for the installation.
Work in Watt-Hours
A useful first calculation is appliance power multiplied by how long you expect to use it. A 40W load running for five hours uses roughly 200Wh. Add the daily loads together to estimate your energy requirement.
Victron’s RV solar guidance similarly recommends starting with energy consumption and then sizing storage and charging around it.
Alternator & DC-DC Charging
A DC-DC charger takes power from the vehicle’s charging system while the engine is running and provides controlled charging to the leisure battery. This is especially useful where battery chemistry or the vehicle’s alternator/control strategy makes a simple relay unsuitable.
- Charger must suit the leisure-battery chemistry.
- Input/output cabling must be sized for current and distance.
- Circuits need appropriate protection.
- Alternator capability and vehicle installation should be considered.
Solar & MPPT
Solar panels feed a charge controller, which manages charging of the leisure battery. MPPT controllers optimise the energy harvested from the panel under changing conditions.
Victron’s 2026 RV solar guidance emphasises sizing the array not only around daily consumption but also around how quickly you need the battery to recover. A system that technically replaces a day’s consumption only after several perfect sunny days is not much use to somebody actually camping in Britain.
- Panel wattage is only part of the story: weather, shade, orientation and season matter.
- Match the controller to the panel voltage/current and battery system.
- Protect and secure roof cabling against water ingress and movement.
Shore Power
Shore power lets the camper use a campsite mains supply. It may simply feed a battery charger, or it can power onboard 230V circuits and an inverter/charger system.
Victron’s current shore-power guide describes the need for appropriate inlet equipment, consumer-unit protection, RCDs, MCBs, suitable cabling and correct protective arrangements.
What an Inverter Does
An inverter converts battery DC power into 230V AC for household-style appliances. The convenience comes at a cost: high-power AC loads can demand very large currents from a 12V battery.
- Choose inverter capacity based on realistic continuous and peak loads.
- Check the battery can deliver the required current.
- Keep high-current DC cabling appropriately sized and routed.
- Do not install a huge inverter simply because a larger number looks reassuring.
Fuses Protect Cables
A fundamental principle is that circuit protection is selected to protect the wiring against excessive current. Main battery feeds and individual circuits need appropriate fusing/breaker protection located and sized for the installation.
- Main positive feeds protected close to the energy source where appropriate.
- Individual circuits protected for their cable/load.
- Correct cable size for current, length and permissible voltage drop.
- Proper terminals, crimping and mechanical support.
- Cables protected from sharp metal edges and heat.
Isolation & Distribution
A clean system has obvious isolation points and organised distribution. You should be able to identify what feeds what without following a red wire through three cupboards and discovering it becomes blue halfway along.
- Label fuses and circuits.
- Use suitable positive and negative distribution points/busbars.
- Provide accessible isolation for major equipment.
- Keep a simple wiring diagram with the van.
Know What the Battery Is Doing
Voltage alone is a limited state-of-charge indicator, particularly while charging or under load. A shunt-based battery monitor measures current flowing into and out of the battery and can provide a much more useful picture of energy use.
- State of charge.
- Current charge/discharge rate.
- Consumed amp-hours/energy depending on monitor.
- Historical trends and unexpected loads on advanced systems.
A Typical System
Conceptually, a modest camper might look like this:
- Starter/alternator → protected DC-DC charger → leisure battery.
- Solar panel → MPPT charge controller → leisure battery.
- Shore power → suitable protected charger → leisure battery.
- Leisure battery → main protection/distribution → 12V loads.
- Optional leisure battery → protected inverter → suitable AC loads.
This is a functional overview, not a wiring diagram. Cable sizes, protection, isolation and AC arrangements must be designed for the actual equipment and installation.
Things Worth Avoiding
- Buying components before calculating energy use.
- No fuse or badly located protection on battery feeds.
- Undersized long cable runs.
- Mixing incompatible charging profiles and battery types.
- Assuming solar panel wattage equals guaranteed daily energy.
- Running every appliance through an inverter when DC alternatives exist.
- Unlabelled wiring and inaccessible fuses.
- DIY 230V work without the competence to design and test it.
Before Building or Upgrading
- List all loads and daily usage
- Calculate approximate Wh/day
- Decide battery chemistry/capacity
- Plan alternator charging
- Plan solar requirement
- Decide whether shore power is needed
- Decide whether an inverter is actually needed
- Size cables and protection properly
- Plan isolation/distribution
- Plan battery monitoring
- Document the finished installation
- Use competent help for safety-critical work
Sources & References
This Just T4s guide is an original high-level camper electrical introduction informed by Victron Energy’s RV technical guidance. It intentionally avoids giving one-size-fits-all wiring sizes or protection values because those depend on the actual design.