Inverter · 12 V → 230 V · cable size
How to connect an inverter to a car battery
An inverter turns the car’s 12 V into 230 V for a laptop, a router, a fridge or power tools — and in a power cut it can keep the essentials running. On the 12 V side it is a very large load, so the whole job is a short, thick, fused connection to the battery.
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Why not the cigarette lighter
The socket circuit is fused at 10–20 A, which is 120–240 W. A 1000 W inverter takes about 1000 ÷ 12 ÷ 0.9 (efficiency) ≈ 93 A from the battery. Anything above a small 150 W unit goes on the battery terminals with its own cables.
Typical loads on 12 V
| Load | Power | Wire length | Current | Fuse | Wire |
|---|---|---|---|---|---|
| Parking lights | 10 W | 4 m | 0.83 A | 2 A | 0.35 mm² (22 AWG) |
| Headlight bulb H7 | 55 W | 3 m | 4.58 A | 7.5 A | 0.75 mm² (18 AWG) |
| Pair of headlights | 110 W | 3 m | 9.17 A | 15 A | 1.5 mm² (16 AWG) |
| Horn | 60 W | 2 m | 5 A | 7.5 A | 0.5 mm² (20 AWG) |
| Wiper motor | 120 W | 2 m | 10 A | 15 A | 1 mm² (17 AWG) |
| Radiator fan | 250 W | 2 m | 20.83 A | 30 A | 4 mm² (12 AWG) |
| LED light bar | 300 W | 4 m | 25 A | 35 A | 6 mm² (10 AWG) |
| Audio amplifier | 1000 W | 5 m | 83.33 A | 125 A | 35 mm² (2 AWG) |
Fuse and cable by inverter power
| Inverter (output) | Battery current | Fuse at the battery | Cable (up to 1.5 m) |
|---|---|---|---|
| 150 W | ≈ 14 A | 20 A | 1.5 mm² |
| 500 W | ≈ 46 A | 60 A | 10 mm² |
| 1000 W | ≈ 93 A | 125 A | 35 mm² |
| 2000 W and more | ≈ 185 A+ | as the maker specifies | as the maker specifies, as short as possible |
The fuse sits within 20–30 cm of the battery on the + cable and is sized for the cable. The − cable is just as thick and goes straight to battery −, not to the body.
Using it in a blackout — safely
- Run the engine: 93 A flattens a typical battery in well under an hour and it may not start afterwards.
- Never run the engine in a closed garage — exhaust gas kills.
- Never plug the inverter into a home socket to “feed the house”. Without a proper changeover switch the 230 V goes back into the grid and can kill a line worker.
- Plug devices straight into the inverter or through an extension lead, and keep the total well below its rating.
See also: Dual battery wiring · Fuse and wire size calculator
Check the cables in the simulator
- Run the live demo: battery, a 125 A fuse at the battery, a switch and a 1000 W inverter on 35 mm² cables.
- Switch it on and click the cables: about 90 A and well under 0.1 V lost.
- Make the cable 10 mm² and watch the overload warning; remove the fuse and see what the simulator says about a short to ground.
- Use the calculator below for your own inverter power and cable length.
Questions
How long will a car battery run an inverter?
Roughly: usable amp-hours ÷ battery current. A 60 Ah battery that should not go below half charge gives about 30 Ah — about 20 minutes at 1000 W, a few hours for a router and a laptop. With the engine running the alternator supplies most of it.
Pure sine or modified sine?
Pure sine runs everything, including fridges, boiler pumps and chargers that hum or overheat on a modified sine. For household devices choose pure sine.
Can I connect the inverter’s ground to the car body?
Use a cable straight to battery −, as thick as the + cable. The body path adds resistance and voltage drop at these currents.
More guides
- Dash cam to the fuse box
- Reverse camera wiring
- Car amplifier wiring
- Dual battery wiring
- DRL wiring diagram
- Winch wiring
- Heated seat wiring
- 12 V socket and USB wiring
- All guides
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