How to Plan a Campervan Electrical System from Scratch

Planning before you buy any parts saves money and avoids the classic van builder mistake: buying components piecemeal that do not work well together. Here is the sequence that works.

Step 1: List your loads (appliances)

Write down every electrical appliance you want in the van. For each, find the wattage (or current draw in amps) from the product label or datasheet. Estimate how many hours per day you will use it.

Common loads to include:

Calculate your daily consumption in Wh (watts × hours/day). Then convert to Ah: Ah = Wh ÷ 12.

Step 2: Size your battery

Your battery must store enough energy for your typical use between charges, plus a buffer.

For LiFePO4 (recommended):

• Size in Ah = daily consumption (Ah) ÷ 0.9 (90% usable)
• Add 50% buffer for low-solar days or higher-than-average use

For AGM:

• Size in Ah = daily consumption (Ah) ÷ 0.5 (50% usable)

Example: 120Ah daily consumption → LiFePO4: 120 ÷ 0.9 = 133Ah, so buy 200Ah → AGM: 120 ÷ 0.5 = 240Ah, so buy 2× 150Ah.

Step 3: Size your solar array

A rough guide for UK use:

• Each 100W of solar provides approximately 30–50Ah per day in summer, 10–20Ah in winter
• Match solar output to daily consumption as closely as possible
• Add more panels if you want a buffer for overcast days or higher winter output

Example: 120Ah daily consumption → 400W solar in summer (provides 120–200Ah) → good headroom.

Step 4: Choose charging sources

Most builds use at least two charge sources:

Solar: Primary off-grid charging. Size as above.

Alternator (via DC-DC charger): Charges while driving. A 30A DC-DC charger at 14.4V = 432W while the engine runs. A 3-hour drive delivers ~130Ah — significant daily input.

Mains hook-up: A 25A charger at campsites. Provides reliable full charging overnight regardless of solar or driving.

Step 5: Choose the inverter (if needed)

Size the inverter for your largest single AC load, with some headroom:

• Kettle (750W): 1,000W inverter
• Induction hob (1,400W): 1,500–2,000W inverter
• Coffee machine (1,300W): 1,500W inverter

A 1,000W inverter handles most van life needs. Go to 2,000W if you want an induction hob or a bean-to-cup coffee machine.

Step 6: Draw a system diagram

Before buying anything, draw the system:

• Battery → ANL fuse → positive bus bar
• Charge sources (MPPT output, DC-DC output, mains charger) → positive bus bar
• Loads (inverter, fuse box) → positive bus bar
• All negatives → negative bus bar → chassis earth

This diagram reveals:

• Where cables route
• What cable lengths you need
• Any conflicts or gaps in the design

Step 7: Size cables and fuses

For each cable run, calculate current and check the cable size against a rating table. Key rule: fuse for the cable, not the load. See our cable size guide for the full table.

Step 8: Make a parts list and budget

With the design complete, list every component:

• Battery
• MPPT charge controller
• DC-DC charger
• Mains charger
• Inverter (if required)
• ANL fuse(s) and holders
• Bus bars (positive and negative)
• Battery monitor / shunt
• Fuse box or DIN rail consumer unit
• Cables (lengths and sizes)
• Connectors and terminals
• Junction boxes, conduit, cable clips

Price each item and compare the total against your budget.

Common planning mistakes

Buying a cheap PWM controller instead of MPPT: MPPT is 20–30% more efficient and required for LiFePO4 configuration. Never use PWM for a lithium system.

Undersizing the battery: Plan for the number of overcast days you expect in your typical trip area. One day's autonomy is not enough for UK autumn/winter use.

Ignoring cable sizing: Long cable runs with undersized cables cause voltage drop, heat, and wasted energy. Calculate every run.

Forgetting the inverter's DC cable: A 2,000W inverter needs 50mm² cable. This is expensive and physically large — factor it into the layout.

FAQ

In what order should I install the electrical system?

Install in this order: battery location → cable routes → fuse holders → bus bars → charge controllers → battery monitor → fuse box → loads. Leave main fuses out until all connections are made and checked.

Do I need a battery monitor?

For any LiFePO4 system or any system relying on solar, a battery monitor (Victron BMV-712 or SmartShunt) is essential. Voltage alone is not a reliable state-of-charge indicator for LiFePO4. A coulomb counter gives accurate SoC.

Can I start small and add to the system later?

Yes — design the system with expansion in mind. Oversize bus bars, leave spare circuits on the fuse box, and run conduit for future cable runs. Adding a second battery or more solar is straightforward if the main cables and bus bars are already sized for it.