Pure Sine Wave Inverters for Campervans: Complete Guide to Choosing the Right Inverter
An inverter converts your 12V battery power to 240V mains electricity so you can use standard household appliances in your van. Most van lifers need one — for laptop charging, running a coffee machine, or powering a TV. But the wrong inverter can damage your electronics, drain your battery, or start a fire.
I have used three inverters. The first was a cheap 300W modified sine wave (£25). It made my laptop charger buzz and killed a CPAP machine power supply within a month. The second was a 1,000W pure sine wave from a no-name brand — it worked but its cooling fan was loud enough to wake me up. The third is a Victron Phoenix 800W — silent, efficient, reliable.
This guide covers everything you need to choose and install an inverter in a UK campervan.
Sine Wave Types
Pure Sine Wave
The inverter produces a smooth, clean AC waveform identical to mains electricity. Every appliance works correctly:
| Appliance | Pure Sine Wave | Why |
|---|---|---|
| Laptop charger | ✓ Works perfectly | The power supply sees a clean waveform |
| CPAP machine | ✓ Essential | Modified sine wave damages CPAP motors |
| Induction hob | ✓ Works | Needs pure sine for electronics |
| Microwave | ✓ Works | Slightly more efficient on pure sine |
| LED lights | ✓ Works | No buzzing or flickering |
| Power tools | ✓ Works | Variable speed tools need clean power |
Modified Sine Wave
A stepped approximation of a sine wave. Cheaper to produce but creates problems:
| Appliance | Modified Sine Wave | Problem |
|---|---|---|
| Laptop charger | ⚠️ Works but can buzz | The power supply overheats, reduces lifespan |
| CPAP machine | ✗ Can damage | Motors run hot, power supplies fail |
| Induction hob | ✗ Usually does not work | Electronics reject the waveform |
| Microwave | ⚠️ Works but less efficient | 10–15% more battery drain |
| LED lights | ⚠️ Can flicker or buzz | Dimmer switches may not work |
| Power tools | ✗ Variable speed fails | Universal motors run but speed control fails |
Inverter Sizing
Calculate Your Maximum Load
List everything you might run simultaneously and add their wattages:
| Appliance | Typical Wattage | Simultaneous Load |
|---|---|---|
| Laptop charger | 60W | 60W |
| Phone charger (×2) | 10W | 20W |
| TV | 40W | 40W |
| Coffee machine | 800W | 800W (peak, while running) |
| Microwave (800W) | 1,200W (input) | 1,200W |
| Induction hob (1,200W) | 1,400W (input) | 1,400W |
Simultaneous usage matters: If you only use one appliance at a time, size for the biggest single load. If you run a TV + laptop + lights at the same time, add them up.
Inverter Size Guide
| Inverter Rating | Can Run | Battery Draw at Full Load | Best For |
|---|---|---|---|
| 300W | Laptop, phone, TV, LED lights | 25A | Minimalists, CPAP users |
| 500W | Above + small coffee machine | 42A | Couples, occasional 240V use |
| 800W | Above + microwave, toaster | 67A | Most van lifers (recommended) |
| 1,000W | Above + induction hob (single ring) | 83A | Heavy 240V users |
| 1,500W | Anything except kettle + microwave together | 125A | Full kitchen use |
| 2,000W | Multiple high-power appliances | 167A | Professional, doubled battery bank |
The sweet spot for most van lifers: 800–1,000W pure sine wave inverter. This runs a laptop, TV, and small kitchen appliances. For a microwave, you need 1,200W+.
Battery Draw
| Inverter Load | 12V Current Draw | 100Ah Battery Runtime | 200Ah Battery Runtime |
|---|---|---|---|
| 100W (laptop + phones) | 8.3A | 8 hours | 16 hours |
| 500W (coffee machine) | 42A | 1.4 hours | 2.8 hours |
| 800W (microwave) | 67A | 0.9 hours | 1.8 hours |
Important: Inverter efficiency is not 100%. A 1,000W inverter drawing 83A at full load is actually draining 85–90A from the battery due to conversion losses. The better the inverter, the smaller the loss. Victron inverters are 93–96% efficient; budget inverters are 80–85%.
Installation
What You Need
| Component | Spec | Cost |
|---|---|---|
| Inverter | Pure sine wave, appropriately sized | £80–400 |
| Battery cable | 25mm² (for 800W) or 35mm² (for 1,000W+) | £2–4/m |
| ANL fuse + holder | 100A (for 800W) or 150A (for 1,000W) | £15–25 |
| 240V RCD | 30mA, 10A single-module | £15 |
| 240V socket | Single gang, flush-mount | £5 |
| Switch (remote) | For turning inverter on/off from living space | £10 |
Step-by-Step
- Location: Mount the inverter within 1m of the battery. High current needs short cable runs. Do not mount in a sealed box — inverters need airflow for cooling.
- Cable preparation: Cut the positive and negative cables to length. Crimp ring terminals on both ends. Use a hydraulic crimper — a hammer crimper does not create a gas-tight connection.
- Fuse: Install an ANL fuse on the positive cable within 30cm of the battery. The fuse protects the cable — size it for the cable rating, not the inverter.
- Connection: Connect positive (fused) to the inverter's positive terminal. Connect negative to the inverter's negative terminal. Torque terminals to the inverter's specification (typically 8–12 Nm).
- Grounding: Connect the inverter chassis ground to the van's chassis ground (bonding point on the inverter).
- 240V wiring: Connect the inverter's 240V output to a single RCD-protected socket. Use 1.5mm² three-core cable.
- Test: Plug in a 50W test load (a lamp). Check the inverter fan runs, the lamp stays on, and the inverter shows normal output voltage (230V ±10V).
Cooling
Inverters generate significant heat at high loads. A 1,000W inverter at full load dissipates 50–80W of heat.
Installation rules:
- Do not mount in a sealed cabinet
- Leave 10cm clearance on all sides for airflow
- The cooling fan needs an air intake and an exhaust — both to the same room (do not vent outside, you would lose heat in winter)
- If the inverter regularly cuts out on high-temperature protection, you need a larger inverter (it is running too hard) or better ventilation
Inverter Features
| Feature | Why It Matters | Look For |
|---|---|---|
| Remote on/off switch | Turn inverter off from bed (saves power from idle draw) | Included or compatible |
| Power-saving mode | Reduces idle draw to <1W when no load is detected | Labeled "ECO mode" or "Power saving" |
| Low-voltage disconnect | Protects battery from over-discharge | Adjustable threshold (11.0–12.0V) |
| Silent fan | Loud fans are annoying in a small van | Temperature-controlled, variable speed |
| Bluetooth monitoring | See power usage on your phone | Victron, Renogy |
Idle Draw
Inverters consume power even when nothing is plugged in. This is called idle draw or quiescent current.
| Inverter Quality | Idle Draw | Annual Loss (if always on) |
|---|---|---|
| Budget (modified sine wave) | 0.8–2.0A | 700–1,750Ah (half a 200Ah battery every 3–5 days) |
| Mid-range (pure sine wave) | 0.3–1.0A | 260–876Ah |
| Premium (Victron, Mastervolt) | 0.1–0.5A | 88–438Ah |
| Eco mode (any brand) | <0.05A | <44Ah |
Always turn the inverter off when not in use. A remote switch makes this practical. Or wire it through a relay that turns on only when the engine is running or via a manual switch.
Recommended Inverters
| Model | Power | Quality | Noise | Price | Best For |
|---|---|---|---|---|---|
| Victron Phoenix 500W | 500W | Excellent | Silent | £180 | Minimalist, CPAP |
| Victron Phoenix 800W | 800W | Excellent | Silent | £240 | Most van lifers |
| Victron MultiPlus 1,200W | 1,200W | Premium | Silent | £450 | + battery charger |
| Renogy 1,000W | 1,000W | Good | Moderate | £120 | Budget pure sine |
| NDS 1,000W | 1,000W | Good | Moderate | £100 | Budget option |
| Giandel 2,000W | 2,000W | Acceptable | Loud | £150 | High-power, budget |
The Victron Phoenix is the standard for UK campervans for good reason. Excellent build quality, silent operation, very low idle draw, and Victron's ecosystem (Bluetooth, remote monitoring, integration with their charge controllers and battery monitors).
Safety
- Fuse the positive cable: Always. Within 30cm of the battery. No exceptions.
- 240V sockets must be RCD-protected: A 30mA RCD (residual current device) between the inverter and the socket. This is a legal requirement for mains voltage in a vehicle.
- Do not run 240V cables alongside 12V cables: Keep them separated by 20cm minimum to prevent interference.
- Ventilation: As discussed above.
- Disconnect when not in use: The inverter remote switch or a manual switch. Idle draw drains your battery silently.
FAQ
Q: Can I run a kettle from my campervan inverter? A: A standard 2kW kettle needs a 2,500W+ inverter. At full load, that draws 180A from a 12V battery. Most van electrical systems cannot sustain this. Use a gas kettle or a 12V immersion heater instead.
Q: How long does a 100Ah battery run a 800W inverter? A: At full load, 67A draw × 0.9 hours = 60Ah. But you should not discharge LiFePO4 below 20%, so usable capacity is 80Ah. Runtime at full load: 72 minutes. In practice, most loads are not full load.
Q: Can I install a campervan inverter myself? A: Yes, if you are comfortable with 12V DC wiring. The 240V AC side requires proper connections and RCD protection. If you are unsure, have a qualified electrician check your 240V installation.
Q: What size inverter do I need for a CPAP machine? A: Most CPAP machines draw 30–60W. A 300W pure sine wave inverter is sufficient. Some CPAP machines have a built-in 12V adapter — even better (no inverter needed).
Q: Do I need a pure sine wave inverter for a laptop? A: Yes, if you care about your laptop's battery and power supply lifespan. A modified sine wave will work but causes the power supply to run hotter. Over months of use, this reduces power supply lifespan.
