Draper 12V DC-AC Inverter, 400W

More power, more possibilities. The Draper IN400/USB is a 400W continuous power inverter that converts 12V DC from a vehicle, caravan or leisure battery into 230V AC mains power — giving you a standard UK three-pin socket and USB charging port wherever you need them. With double the continuous output of the IN200/USB and an 800W peak capacity to handle demanding start-up loads, the IN400/USB opens up a wider range of appliances and use cases for caravanners, boat owners, HGV drivers and anyone else who needs reliable mains-equivalent power away from the grid.

Key Features & Benefits

400W Continuous Power — Double the Capacity of the 200W Model

Where the IN200/USB handles light loads such as laptops, phone chargers and LED televisions, the IN400/USB steps up to power a broader range of appliances that demand more from an inverter. A continuous 400W output — backed by an 800W peak capacity for start-up surges — means you can confidently run larger laptops, power tools, small cooking appliances, fans, and equipment that draws more current during operation. For anyone who found a 200W inverter limiting, the IN400/USB is the natural next step.

Standard UK Three-Pin Socket Output

The IN400/USB outputs through a standard UK three-pin socket, making it immediately compatible with any UK-plug appliance without the need for adaptors or converters. Connection is as straightforward as plugging into a wall socket at home — the only difference is that the power comes from your 12V battery rather than the mains grid.

Built-In USB Charging Port

A dedicated USB port allows you to charge mobile phones, tablets, GPS units and other USB-powered devices at the same time as running a mains appliance through the three-pin socket. It's a practical dual-output arrangement that eliminates the need for a separate car charger and keeps all your devices powered from a single compact unit.

Overload Alarm for Appliance and Inverter Protection

Exceeding an inverter's rated capacity risks damaging both the connected appliance and the inverter itself. The IN400/USB is fitted with an overload alarm that activates when the power draw approaches the unit's limit, giving you advance warning to reduce the load before any damage occurs. It's an important safeguard when running appliances whose actual wattage draw may be higher than expected.

Reverse Polarity Protection

Connecting battery leads incorrectly is a common mistake — particularly in cramped engine bays or low-light conditions. The IN400/USB includes reverse polarity protection that safeguards the inverter and your vehicle's electrical system against the consequences of an accidental incorrect connection, giving you peace of mind during installation and reconnection.

Ideal for Caravans, Boats, HGVs and Motorhomes

The IN400/USB is well-suited to the environments where 230V power is needed but a mains hook-up isn't available. The higher 400W output makes it particularly useful for caravanners running small cooking appliances or heating devices, boat owners powering electronics and equipment off a leisure battery bank, HGV and van drivers needing to run tools or power a small device during rest periods, and motorhome users requiring more headroom than a 200W unit provides.

Modified Sine Wave Output

The IN400/USB generates a modified sine wave output, which is compatible with the large majority of everyday appliances including laptops, televisions, LED lighting, chargers, fans and many small kitchen and personal care devices. For highly sensitive equipment — certain medical devices, precision audio equipment or some specialist electronics — a pure sine wave inverter would be more appropriate. For the vast majority of caravan, boat and vehicle use cases, modified sine wave is entirely adequate.

Who Is This For?

The Draper IN400/USB is the right choice for:

• Caravanners and motorhome users who need more than a basic 200W inverter can provide — particularly those running small cooking appliances, heaters or higher-draw devices between hook-up points
• Boat and narrowboat owners powering a broader range of onboard electronics and appliances from a leisure battery bank
• HGV and van drivers who need to run tools, power laptops or charge multiple devices during rest periods and overnight stops
• Outdoor and off-grid enthusiasts who want the flexibility to run standard UK appliances from a vehicle or standalone leisure battery
• Tradespeople and site workers needing a portable 230V power source from a vehicle battery when site power is unavailable
• Anyone upgrading from the IN200/USB who has found 200W insufficient for their power needs

What Can a 400W Inverter Power?

The IN400/USB's 400W continuous output handles a meaningfully wider range of appliances than a 200W unit. As a general guide:

Always check the wattage rating of your appliance before use. Where an appliance lists both running and start-up wattage, the start-up figure should remain within the 800W peak rating.

Frequently Asked Questions

What is the difference between 400W continuous and 800W peak power? Continuous power (400W) is the maximum the inverter can sustain during normal ongoing use. Peak power (800W) is the brief surge capacity available when an appliance first starts up — motors, compressors and some power tools momentarily draw significantly more current at start-up than they do once running. The 800W peak ensures the IN400/USB handles this start-up demand without tripping, even if the appliance's running wattage sits comfortably within the 400W continuous limit.

How does the IN400/USB differ from the IN200/USB? The IN400/USB delivers 400W continuous and 800W peak output — double the capacity of the IN200/USB's 200W continuous and 400W peak. Both share the same UK three-pin socket output, USB port, overload alarm, reverse polarity protection and modified sine wave technology. The IN400/USB is the better choice for users who need to run higher-wattage appliances or who want more headroom for demanding or multiple simultaneous loads.

What is a modified sine wave and does it matter? A modified sine wave approximates the smooth waveform of standard mains electricity. It is compatible with the vast majority of common appliances — laptops, televisions, chargers, fans, LED lighting and most small domestic appliances. Certain sensitive equipment such as some medical devices, high-end audio systems and specific motor-driven tools may benefit from a pure sine wave inverter. For everyday caravan, boat and vehicle use, modified sine wave is suitable for almost all typical applications.

Will the IN400/USB drain my vehicle battery? Running the inverter at higher loads will draw significant current from your battery. For sustained use or higher-wattage applications, running the engine or connecting to a dedicated leisure battery is strongly recommended. Using the inverter from a standard starter battery alone — particularly at loads approaching 400W — risks draining the battery to a level that prevents the vehicle from starting.

Can I use the USB port and mains socket simultaneously? Yes. The USB port and three-pin mains socket operate independently, allowing you to charge a mobile device and run a mains appliance at the same time.

How do I connect the IN400/USB to my battery? The unit connects directly to a 12V battery via the supplied leads — positive terminal to positive, negative to negative. The reverse polarity protection feature safeguards the inverter and your vehicle's electrical system if connections are made incorrectly.

Full Specification