Campervan Electrical System Guide: How Every Part Fits Together

Wiring is the part of a van build that makes most people nervous. There are a lot of boxes, a lot of acronyms, and plenty of forum threads that disagree with each other. Here is the good news: a campervan electrical system only has four jobs. It stores power, charges that power back up, converts it into the kind your appliances need, and sends it safely to where it is used.

Once you can see those four jobs, every part has an obvious place. This guide walks through each one in plain English, with examples you can picture, so you can plan an off-grid system with confidence before you buy a single part.

Start here: electricity is like water

You do not need an engineering degree to wire a van. You need four words, and a garden hose is the easiest way to remember them.

• Volts are the pressure in the hose. Most vans run on 12 volts, the same as the vehicle itself.
• Amps are how much water is flowing. More flow needs a fatter hose, which is why big appliances need thick wire.
• Watts are the work getting done. Multiply volts by amps and you get watts. A 12V fridge pulling 4 amps is using about 48 watts.
• Amp hours are the size of the tank. A 100 amp hour battery holds twice as much as a 50 amp hour battery.

That is the whole vocabulary. Everything below is just these four ideas put to work.

The four jobs of a campervan electrical system

Here is the whole system on one page. Power comes in on the left, sits in the battery bank in the middle, and goes out to your lights and appliances on the right.

1. Store power in a battery bank.
2. Charge the bank from the alternator, the sun, or a plug.
3. Convert 12V battery power into 120V household power when you need it.
4. Distribute power to each light and appliance through fuses and breakers.

Let's take them one at a time.

Job 1: Store power in a battery bank

Your van already has a battery under the hood. That one starts the engine, and you want it left alone. The battery bank that runs your fridge, lights and fan is a second, separate set of batteries usually called the house bank.

For most off-grid builds today, the house bank is lithium (the full name is lithium iron phosphate, or LiFePO4). Compared with older lead-acid and AGM batteries, lithium is lighter, charges faster, lasts for far more cycles, and lets you use most of what is in the tank.

Battery size is measured in amp hours. To give you a feel for it, a single 100Ah lithium battery holds about 1,280 watt-hours. That is enough to run a typical 12V fridge on its own for close to three days.

How big should yours be? That depends on what you plan to run, and it is the subject of the next post in this series. For now, know that most weekend vans land between 100Ah and 200Ah, and most full-time vans land around 400Ah.

Browse our campervan batteries, including LiTime and Victron Energy lithium. One tip: LiTime batteries have their battery management system built in, while Victron lithium batteries are designed to work with a separate Victron BMS, so they suit full Victron builds.

Job 2: Charge it back up

A battery bank is a tank, and a tank is only useful if you can refill it. There are three ways to do that in a van, and most off-grid builds use at least two.

Charging while you drive: the DC-DC charger

Your engine's alternator makes electricity whenever you are driving. A DC-DC charger sits between the starter battery and the house bank and takes a safe, steady share of that power.

Why not just connect the two batteries with a cable? Lithium batteries are hungry. Left to themselves, they will try to pull more current than many alternators are happy to give. A DC-DC charger sets a limit, such as 30 or 50 amps, and gives the lithium bank the charging voltage it wants. A 30 amp charger adds roughly 30Ah for every hour on the road.

See the Victron Orion-Tr Smart 12/12-30A and Orion XS 12/12-50A DC-DC chargers.

Charging from the sun: solar panels and an MPPT controller

Solar panels on the roof make power whenever the sun is up. They cannot connect straight to a battery, though. A solar charge controller goes in between, and the type to buy is called MPPT. Think of it as a smart gearbox that squeezes the most charge out of whatever sunlight you have.

As a rough guide, 400 watts of panels can put back 80 to 120Ah on a clear summer day. In a Pacific Northwest winter, expect a fraction of that. Solar is wonderful for long stays in one spot, and it pairs well with a DC-DC charger for cloudy weeks.

Browse solar charge controllers, such as the Victron SmartSolar MPPT 100/30.

Charging from a plug: shore power

Shore power is the campground pedestal, or the outlet on the side of your house. You plug the van in through a weatherproof inlet, and a charger turns that 120V household power into charge for your battery bank. It is the fastest way to fill up, and it is handy for topping off before a trip or keeping batteries healthy over winter.

See the SmartPlug 30 amp inlet.

Job 3: Convert 12V into household power

Batteries store DC power at 12 volts. Lights, fans, 12V fridges, USB ports and water pumps run on that directly. Anything with a regular wall plug needs 120V AC, and that is the job of the inverter.

Do you need one? Ask yourself what you want to plug in.

• No inverter needed: lights, roof fan, 12V fridge, phone and laptop charging from 12V or USB-C, water pump, diesel heater.
• Inverter needed: induction cooktop, microwave, coffee maker, hair dryer, air conditioner, power tool chargers.

Many builds use an inverter/charger, which is one box that does two jobs. It makes 120V from your batteries when you are off grid, and it charges your batteries when you are plugged into shore power. It also switches between the two on its own.

One thing to know before you shop: inverters are sized in VA, and the usable watts are a little lower. A 3000VA inverter/charger delivers around 2,400 watts continuously, which is plenty for an induction cooktop or a microwave, one at a time.

Inverters are also the thirstiest part of the system. A 1,500 watt cooktop pulls well over 100 amps from a 12V battery bank, so the inverter, the cables and the battery bank all have to be sized as a team.

Browse campervan inverters, including the Victron MultiPlus 12/2000 and MultiPlus-II 12/3000.

Job 4: Distribute power safely

The last job is getting power from the battery bank to each light and appliance without anything overheating. This is the part that keeps your van safe, so it is worth slowing down for.

The 12V side

Your 12V loads each get their own circuit from a fuse block. It works just like the fuse box in a car: one fuse for the fridge, one for the fan, one for the lights, and so on. If something shorts out, that one fuse blows and everything else keeps working.

The 120V side

Your outlets are fed from a small breaker panel, much like the one in a house. Outlets near a sink should be GFCI protected, the same kind with the test and reset buttons you see in a bathroom.

The heavy connections

The battery bank, inverter and chargers all carry big currents, and they need to meet somewhere tidy. That place is a bus bar or a distributor such as the Victron Lynx Distributor, which gives every heavy cable its own bolted connection and its own fuse. It beats stacking five cable lugs on one battery terminal.

One rule for fuses

A fuse protects the wire, not the appliance. If a wire carries more current than it is rated for, it gets hot. The fuse is the weak link that fails first, on purpose. So every wire leaving the battery gets a fuse sized for that wire, placed as close to the battery as you can manage. Add a main disconnect switch as well, so you can shut the whole system off in one move.

Keep an eye on it: battery monitoring

Lithium batteries hold nearly the same voltage from full down to almost empty, so a simple voltage gauge will tell you very little. What you want is a monitor with a shunt. A shunt counts every amp going in and out of the bank, like a fuel gauge that actually measures fuel.

• Victron SmartShunt: the simple option. No screen, reads on your phone.
• Victron BMV-712 Smart: the same idea with a small round display for the wall.
• Victron Cerbo GX: the brain for a full Victron system. Paired with a GX Touch display, it shows solar, shore power, battery and inverter on one screen.

Two example systems: weekend van and full-time off-grid van

Every build is different, but most land near one of these two. Use them as a starting point, not a shopping list.

If you would rather skip the wiring diagram altogether, our Ready-to-Install 400Ah Campervan Electrical System arrives as one self-contained unit.

Where to start your own build

Plan on paper first. It is far cheaper to erase a line than to re-run a cable.

1. List what you want to run. Be honest about the coffee maker.
2. Size the battery bank to cover a day or two of that list.
3. Choose your charging sources. Pick at least two of driving, solar and shore power.
4. Decide on an inverter based on your biggest 120V appliance.
5. Draw a wiring diagram with a wire size and a fuse size on every line.
6. Build it, then test each circuit before you close up the walls.

A word on safety. A 12V battery bank can deliver hundreds of amps, which is enough to melt a wrench or start a fire. The 120V side can give a dangerous shock. Disconnect the battery before you work, use the right wire and fuse sizes, and if you are not sure about something, have it checked before you power it up.

Campervan electrical FAQ

Can I build a campervan electrical system myself?

Yes. Plenty of first-time builders wire their own vans. The 12V side is very approachable with good crimps, the right wire and the right fuses. Take extra care with the 120V side, and consider having a professional review your plan or check your finished work.

Do I need solar if I have a DC-DC charger?

Not always. If you drive most days, a DC-DC charger alone can keep a modest battery bank full. If you like to park in one place for several days, solar is what keeps the fridge running. Most off-grid vans are happiest with both.

Do I need an inverter in my van?

Only if you want to run appliances with a regular wall plug. A van with a 12V fridge, LED lights, a fan and USB charging can skip the inverter completely and save money, space and battery power.

Should my campervan be 12V or 24V?

Most vans are 12V, and that is the right choice for small and medium systems because 12V appliances are easy to find. Larger systems with big inverters sometimes move to 24V to keep cable sizes manageable. We will cover that choice in its own post later in this series.

Ready to power your van?

Shop our full range of campervan electrical and power components. If you would rather have it designed and installed for you, our team builds complete off-grid systems at our shop in Washougal, Washington. Take a look at our electrical services or get a quote.