12V fridges: sizing, running costs and what actually matters

The fridge is the single biggest quality-of-life upgrade in vehicle-based camping, and it is also the component that determines the size of everything else in your electrical system. Work out the fridge first and the battery, charging and solar decisions follow from it.

Compressor, not thermoelectric

The first fork in the road, and it is not a close call.

Thermoelectric coolers use a Peltier element and can only achieve a fixed differential below ambient temperature, typically around 20 degrees. On a 40 degree day that means a 20 degree cooler, which is not refrigeration. They are cheap, and they are the wrong tool for Australian conditions.

Compressor fridges work the way a domestic fridge does and hold a set temperature regardless of what is happening outside. They cost several times more and they are what you want.

There is also a three-way option running on 12V, 240V or gas, common in caravans. They are quiet and they work well on gas, but they are absorption units, they need to be reasonably level to work properly, and their 12V performance is poor. For a vehicle-based setup, a compressor fridge is the standard answer.

Sizing it

Bigger is not better, because every litre costs money to buy, power to run, space in the vehicle and payload you may not have.

• 35 to 45 litres suits a couple for about a week between resupply. This is the most common size for a reason.
• 60 to 75 litres suits a family, or longer remote stints.
• Dual zone models run as fridge and freezer at the same time. Genuinely useful for long remote trips where you are carrying meat; unnecessary for a weekend.

Something worth naming: a larger fridge gets filled. Not because you need the food, but because the space exists. That is weight, and weight is the constraint most touring builds hit first. There is more on that in GVM upgrades explained.

What it actually costs to run

The figure that matters is daily consumption in amp-hours, and it moves enormously with conditions.

A typical 40 litre fridge might draw somewhere in the range of 20 to 40 amp-hours per day. The compressor cycles rather than running continuously, so the duty cycle is what determines consumption, and duty cycle is driven by:

• Ambient temperature, which dominates everything else. The same fridge draws vastly more in the north in October than in Victoria in April.
• How often it is opened. Cold air falls out of a front-opening fridge every time the door opens, which is why almost all touring fridges are top-opening chest designs.
• How full it is. A full fridge holds temperature better than an empty one, because the contents are thermal mass.
• Sun and airflow. A fridge in direct sun, or boxed in with no ventilation, runs far harder.

Two cheap interventions cut consumption meaningfully: an insulated fridge cover, and keeping it shaded with clear space around the vents. Both are worth more than they cost.

It decides your electrical system

Once you know the daily draw, the rest follows. Multiply by the number of days you intend to sit without driving or good sun, and that is your usable battery capacity requirement.

Usable is the operative word. A lead-acid battery gives you roughly half its rated capacity before you start shortening its life, while lithium gives you most of it. A 100Ah lithium battery does the work of roughly a 200Ah AGM at around half the weight.

The full working through of battery chemistry, DC to DC charging and solar sizing is in dual battery and 12V systems.

The one component worth naming here is a shunt-based battery monitor. Voltage alone is a poor guide to state of charge, and with lithium it is nearly useless because the voltage curve is flat across most of the usable range. A monitor turns a guess into a number, and it changes behaviour while there is still time to act.

Mounting it

A slide is not a luxury. A fridge you cannot open without unloading the vehicle is a fridge you stop opening, and then you are carrying 30kg of dead weight.

Ventilation is not optional. The compressor removes heat from inside the box and rejects it out the vents. Enclose those vents and the fridge runs continuously, consumes far more power and wears out sooner.

Secure it properly. A loaded 40 litre fridge is a heavy object. Unrestrained in a rollover or a heavy stop it becomes a projectile, and this is one of the more common serious injuries in touring accidents.

What to look for

1. Compressor, not thermoelectric.
2. A brand with a serviceable compressor and available parts, because a dead compressor in a remote area is an expensive lesson.
3. Low voltage cut-out, so the fridge protects the battery rather than flattening it.
4. A drain plug, because eventually something leaks inside it.
5. A basket, so you are not unpacking the whole fridge to reach the bottom.

Camp cooking that goes alongside it is covered in building a camp kitchen you will actually use.