12V Fridge Power Consumption in a Campervan

A compressor fridge may be one of the smaller appliances in a campervan, but it is usually the load that runs for the longest. That makes 12v fridge power consumption central to leisure-battery sizing. Get the calculation wrong and a battery that looks generous on paper can be low after one night off-grid.

The useful figure is not the fridge’s maximum amp draw alone. You need to know how much energy it uses across a full 24 hours, in the temperatures and conditions your van will actually see. A fridge cycling in a shaded UK car park in March behaves very differently from one working hard in a south-facing van on a warm July afternoon.

How 12V fridge power consumption is measured

A 12V compressor fridge commonly draws around 3A to 5A while the compressor is running. Larger units can draw more, and the figure will vary with compressor speed and supply voltage. That running current is only one part of the picture because the compressor switches on and off as required.

For example, a fridge drawing 4A and running for half of every hour uses roughly 48Ah in 24 hours:

`4A × 12 hours = 48Ah per day`

If it runs for only a quarter of the day, the same fridge uses 24Ah. If it runs almost continuously in hot conditions, it could use 80Ah or more. This is why a single amp rating is not a reliable daily consumption estimate.

Some fridge manufacturers state consumption in amp-hours per 24 hours, while others use watt-hours. Both can be useful. To convert watt-hours to approximate amp-hours at 12V, divide by 12. A fridge rated at 480Wh per day, for example, uses about 40Ah per day at 12V. In practice, system voltage varies, so treat this as a planning figure rather than an exact measurement.

Compressor fridges versus absorption fridges

For most modern campervan electrical systems, a 12V compressor fridge is the practical choice. It cools efficiently from the leisure battery, works when the vehicle is level or slightly off-level, and suits solar-supported off-grid use.

An absorption fridge can run on gas, mains electric or 12V depending on the model. Its 12V mode is generally intended for use while driving, supplied through a properly controlled vehicle circuit. It can draw a high, continuous current and is not normally suitable for running from a leisure battery while parked. Do not assume that a fridge labelled 12V is automatically a low-draw compressor unit.

What makes a campervan fridge use more power?

The compressor runs to remove heat from the fridge cabinet. Anything that adds heat, lets cold air escape or prevents the fridge shedding heat effectively increases its duty cycle.

Ambient temperature is the biggest variable. A fridge in a well-insulated van parked in shade has a much easier job than one beside a sun-heated window. The internal temperature setting matters too. Keeping a fridge at 2°C rather than 5°C costs energy, and a freezer compartment adds a meaningful load.

Ventilation around the compressor and condenser is equally important. Refrigeration installations need the clearances specified by the fridge manufacturer, including a route for warm air to escape. Packing the appliance tightly into furniture without ventilation can make it run longer, perform poorly and shorten component life. This is a common issue in DIY units where appearance has been prioritised over service space and airflow.

Frequent door opening, loading warm food, poor door seals and an overfilled or empty cabinet can also affect use. A reasonably full fridge holds its temperature better when opened, but air still needs room to circulate. Pre-chilling food at home before a trip reduces the first day’s load considerably.

Size the battery around daily use, not brochure figures

Start with the fridge manufacturer’s quoted 24-hour consumption at a stated ambient temperature. Then allow for real-world variation. If the quoted figure is 35Ah per day in mild conditions, planning around 45Ah to 55Ah per day gives more realistic headroom for summer weather, warm groceries and regular access.

Next, add the rest of the van’s daily electrical loads. Lighting may be modest with LEDs, but water pumps, diesel heaters, USB charging, fans, routers, televisions and inverters soon add up. A fridge should not be assessed in isolation when the same leisure battery also supports the rest of the conversion.

Battery chemistry changes the usable capacity. A 100Ah lead-acid, AGM or gel battery should not routinely be taken deeply flat. Using around 50Ah before recharging is a sensible planning approach for battery life. A quality 100Ah lithium battery commonly provides closer to 80Ah to 100Ah of usable capacity, depending on its battery management system and the installation limits.

That distinction matters. A fridge using 45Ah per day could consume most of the sensible usable capacity of a 100Ah AGM battery in one day before any other loads are considered. The same fridge on a 100Ah lithium setup leaves substantially more usable energy, although it still needs a reliable way to recharge.

A practical overnight example

Take a medium compressor fridge using 40Ah over 24 hours. Add 8Ah for lights and device charging, 10Ah for a diesel heater on a cool evening, and 7Ah for a water pump and occasional fan use. The daily total is about 65Ah.

For a one-night stop, a 100Ah lithium leisure battery may be adequate if it starts properly charged. For several nights without driving, it is not enough to focus on battery capacity alone. You need to replace roughly 65Ah each day through solar, a battery-to-battery charger, mains hook-up or a combination of these.

Account for charging losses and poor weather

Solar is useful, particularly from spring to early autumn, but panel wattage is not the same as guaranteed daily charge. A 200W roof-mounted panel may produce enough to cover a fridge and basic loads on a clear summer day. In winter, under cloud, low sun angles, shading or a dirty panel, output may be a fraction of that.

A battery-to-battery charger can provide dependable charging while driving, but journey length matters. A short run to the shops will not necessarily replace a day of fridge use, particularly where the charger is limited or the battery is already low. Mains charging remains the straightforward option for campsites, storage and pre-trip preparation.

Plan an electrical system around the least favourable reasonable conditions, not the best day you can imagine. If the van will be used year-round in the UK, allow for several dull days and cold nights with heater use. If it will mainly be a summer weekend vehicle, the required battery and charging setup may be simpler.

Installation details that protect fridge performance

Correct cable sizing and circuit protection are not optional. A compressor fridge can suffer low-voltage cut-outs if cable runs are undersized, connections are poor or shared circuits introduce voltage drop. The fridge may appear faulty when the real problem is a weak supply at the appliance.

Run an appropriately sized dedicated feed from the fused distribution system, follow the appliance manufacturer’s fuse recommendation and make sound crimped connections. Locate the leisure battery and distribution equipment sensibly to keep high-current cable runs practical. A battery monitor is also worth fitting: it shows actual amp draw, state of charge and daily consumption instead of leaving you to guess.

Insulation supports fridge efficiency indirectly. Proper thermal insulation and window coverings reduce solar gain and help stabilise the cabin temperature. They will not turn an unsuitable electrical system into a capable one, but they reduce the heat the fridge has to fight, especially when the van is parked up.

Reducing fridge use without compromising food safety

Set the fridge to a safe temperature, generally around 3°C to 5°C, rather than turning it down unnecessarily. Keep the van shaded where practical and use windscreen and window coverings in direct sun. Check that external vents and compressor airflow paths are clear before a trip.

Cool the fridge on mains power before loading if possible, then stock it with chilled food and drinks. Avoid using it as a place to cool several warm bottles at once. If you are touring with limited charging, make fewer, more deliberate door openings and check the door seal is clean and closing properly.

The best setup is not automatically the largest battery or the biggest solar panel. It is a matched system: a correctly installed compressor fridge, realistic daily consumption figures, usable battery capacity and a charging plan that suits how the van is actually used. Build around those figures and the fridge becomes a dependable part of the conversion rather than the reason the lights go out.