Portable fridges and coolers look much the same from the outside – they’re all insulated boxes with lids – but there are significant differences in the way they work and the type of energy they use.
It’s necessary to know something about the ebbs and flows of the cooling business if you want to be sure of buying the right unit for your needs.
Ice Box Cooler
The simplest and by far the cheapest type of food and drink cooler is the faithful ‘Esky’: an insulated box with an insulated lid, into which you put ice that someone else has created. When you buy bagged ice, you’re actually buying a ‘slug’ of pre-packaged refrigeration.
We’ve been checking these units for their insulating quality over many years and Coleman units are relatively expensive, but consistently do better than most others, keeping contents cool for several days, even in high ambient temperatures. Check out our icebox test.
Plusses: Low price; relatively portable on built-in wheels; doubles as a picnic ‘seat’; can be used for general storage when not cooling; zero maintenance.
Minuses: Bagged ice is not available in remote areas.
Portable fridge updates
Since our previous rundown on the various types of mobile refrigeration, back in 2018, the market has changed and prices of some brands have dropped considerably. Also, progress in lithium battery technology and solar charging has altered the playing field.
When we last wrote about small fridges there was some competition for the 12V/24V compressor-operated fridge from thermoelectric cooler/heaters. However, lower RRPs for compressor fridges have virtually sidelined what used to be the much cheaper thermoelectric alternatives.
Also, like thermoelectric cooler/heaters, some of the latest small compressor fridges are designed for seat mounting, or as replacements for centre console bins.
The compressor type is a true refrigerator that can operate as a freezer or a fridge, where the thermoelectric type is a ‘differential’ cooler, able only to drop temperature in relation to the ambient and the ambient in a closed vehicle can be very high.
RRPs in mid-2022 for 15-litre thermoelectric cooler/heater units were around the $200 mark and you could buy a 15-litre compressor fridge for that money. The OzTrail range and Jaycar’s Brass Monkey portable fridges had halved the price you previously had to pay for a compressor fridge.
There are still a number of thermoelectric cooler boxes on the market, despite the closed price gap between an ‘esky’ and a true fridge.
Thermoelectric types employ an effect that occurs between two closely-coupled, dissimilar materials. When an electrical current is passed through the materials a temperature variation occurs and can be switched to create heat inside a container or cooling.
Claims for thermoelectric performance usually quote an internal temperature: ’22 degrees below ambient’ or similar. In that respect they’re not reliable for storing temperature-critical, perishable contents. However, the thermoelectric effect works both ways, so these units can be set to heat their contents, up to around 65ºC.
At this stage of development, thermoelectric coolers work as compact means of cooling or heating non-critical consumables.
They’re not very efficient, with current draws around 4-5 amps, or in the same province as compressor-type ‘real’ fridges, but they have no moving parts and some are designed specifically for car-seat stowage, with integrated seat belt mouldings. Some can work as a centre-seat armrest.
Plusses: low cost; noiseless; compact; able to heat or cool contents.
Minuses: relatively inefficient; no guaranteed cold temperature.
The most popular form of in-vehicle refrigeration is the compressor-type fridge and sizes vary from small models with single lifting handles to chest-type large units, with handles on each end. The operating principle is similar to that in your household fridge.
Most portable compressor-type fridges are 12V/24V/240V compatible, so can run off a 12V power outlet, a 24-volt truck power outlet, a 240V inverter or a mains socket. Most compressor-type fridges use a reciprocating compressor, while Engel has a ‘swing motor’ type. The advantage of the Engel Sawafuji compressor is that it can work on slide slopes, so is a good choice for serious off-roaders.
Many travellers use a small chest-type fridge – 15-30-litres capacity – that can keep lunch and drinks cold during the driving day, in addition to the main fridge. RRPs for 15-30-litre chest-type fridges were in the $200-$800 range. Larger ones, up to 80 litres, ranged up to two grand.
Alternative fridges for built-in fitment are drawer-types and front-opening ones that are mainly in the $450 – $2000 range.
The most popular form of portable refrigeration is the portable, compressor-type fridge.
The operating principle is simple enough: the fridge piping contains a gas that liquefies at low temperatures and this gas is pressurised through fan-cooled condenser coils that are located outside the food storage area.
As the gas sheds its heat through the coils it condenses into liquid, still under pressure and is forced through an expansion valve (tiny hole), into a low-pressure area created by the suction effect of the compressor. This action causes the liquid to vapourise and drop its temperature.
Compressor suction pulls this cold gas through the evaporator coils that are inside the food storage area, lowering the temperature of the contents and warming the gas, which then passes through the compressor and the cycle continues.
Portable compressor-type fridges are 12V/240V compatible, so can run off a car power outlet, inverter or mains plug. Waeco and most compressor-type fridges use a reciprocating compressor, while Engel has a ‘swing motor’ type.
A compressor-type fridge can run off car alternator power while the vehicle is being driven, but it needs auxiliary electrical power when the engine isn’t working.
A deep-cycle auxiliary battery is a common source of 12-volt power and can normally power a fridge for between one and three days, without re-charging, depending on ambient temperature and battery capacity. A solar panel can run a fridge when sunlight is available, or it can be powered at any time by a generator.
Plusses: can operate as a fridge or a freezer and some models can do both; median pricing; relatively portable with handles on each end.
Minuses: needs to cycle on and off periodically, so electrical power needs to be available 24/7 while cooling; fridge noise can be a problem at night.
Fridge power when the engine isn’t running
A compressor-type fridge can run off alternator power while the vehicle is being driven, but it needs auxiliary electrical power when the engine isn’t working.
Your standard starting battery is primarily designed for engine starting. Starting batteries have thin plates that provide plenty of cold-cranking amps, but they’re not designed for constant output of mid-amp current flows.
The compressor fridges we’ve tested typically draw 4-6 amps and cycle on and off according to the desired temperature inside the fridge and the in-cab ambient. That compressor operation varies from around one third of the time to three quarters of the time. The latter high-cycling case is when the fridge is operating as a freezer, in high ambients.
Our testing has shown that even a fully-charged, non-sulphated, lead-acid starting battery cannot run a fridge overnight – even as a fridge, not a freezer – and have enough grunt left in the morning to start the vehicle. Also, experts warn that behaviour will radically shorten battery life.
The solution for overnight operation is a dedicated, deep-cycle fridge battery.
A 100 amp-hour, deep-cycle auxiliary battery is a common source of 12-volt power and can normally power a fridge for between one and two days, without re-charging, depending on ambient temperature.
The battery is charged by the vehicle alternator when driving and can be switched to power the fridge automatically when the engine is turned off. However, with good weather and sufficient solar panel charging power, the battery can remain charged and power the fridge indefinitely.
Back a few years ago, that auxiliary battery could be an absolute pain to stow, with the need for hydrogen gas venting and acid drainage in the case of a leak. Also, a 100 amp-hour battery weighed around 40kg. Absorbed glass mat (AGM) and gel batteries did away with the need for gas exit and drainage, but still weighed the same, or more.
Lithium battery development has changed all that and today’s deep-cycle, lithium-ferro-phosphate (LFP) battery weighs in at only 11-14kg. And needs no gas or drainage vents.
If that battery capacity is increased to 200-300Ah or more, the LFP battery can also power an air-conditioner overnight. We’re currently testing an EcoFlow portable 48V power pack that can do all that and power a microwave and coffee maker, as well.
An alternative to a fixed auxiliary battery is a portable power pack – a battery in a carry case – that plugs in to charge while the vehicle is operating and then powers the fridge overnight. We’ve used a Thumper AGM power pack for several years and it does the job quite well.
‘Ice bank’ fridges
Another alternative is a eutectic or ‘ice-bank’ fridge that employs the compressor refrigeration cycle, but adds a significant additional component.
Instead of evaporator coils (the coils that get cold) being inside the food compartment, they’re housed in a tank that surrounds the food compartment. Inside the tank is a liquid that freezes as a result of the refrigeration cycle and this external ice-bank is what cools the contents of the food storage area.
A eutectic fridge operates with alternator power when the engine is working and, in the case of an overnight stop, won’t need to operate again until the engine starts up next morning, so there’s no compressor cutting in and out during the night and no need for battery power. The ice-bank keeps the contents cold in the meantime. Many boats have custom-made eutectic fridges built in.
As with a straight compressor-type fridge, a eutectic unit can function as a freezer, or a combination fridge/freezer, but freezer temperature control overnight in high ambients isn’t as reliable as a normal compressor fridge running on battery power.
Our testing in real-world conditions showed that our Autofridge eutectic fridge uses less electrical power when working on the same cooling duty-cycle as a straight compressor-type fridge.
However, portable eutectic fridges are no longer made in Australia, so for a eutectic fridge you need to talk to marine eutectic fridge suppliers, who can design and make a custom unit to fit in a 4WD or RV just as they do for yachts and cruisers.
Plusses: efficient cooling; ‘overnight’ power-free potential.
Minuses: high initial price; bulkier and heavier than a straight-compressor-type fridge for its internal capacity; only custom-made ones available.
Absorption-type Portable Fridge
An absorption-type fridge uses heat energy, rather than an electrically-operated compressor to pump refrigerant around the system.
As the name suggests, the refrigerant is released from solution and absorbed again during the process.
Heat, sourced from 12-volt, 240-volt or LPG supply, is used to raise the temperature of a strong ammonia/water solution, so that most of the ammonia evaporates.
From there the ammonia passes through a fan-cooled condenser, where it becomes liquid, before passing through a restrictor that causes it to evaporate. This action cools the gas as it passes through tubes in the food storage area, drawing heat from the contents.
The warmed gases then flow into an absorber, filled with the weak ammonia solution, where they’re absorbed, forming a strong solution once more and the cycle repeats.
Absorption-type fridges aren’t as energy efficient as compressor-type fridges, but they have advantages that make them popular as the main fridges in caravans. The most obvious one is silence! With no moving parts, an absorption-type fridge won’t disturb your slumber.
Another major advantage is the ability to operate on 12-volt, 240-volt and LPG power. However, our experience over many years of travel is that 12-volt operation is much less efficient than 240V or LPG.
The reason for this is simple: electrical energy is used least efficiently in a radiant-heat application – the heating element for an absorption fridge – but is 90+ percent efficient when powering an electric motor, such as a fridge compressor.
To supply current for an absorption-type portable fridge in a vehicle it’s necessary to have a powerful alternator and guaranteed 12V power delivery around 10 amps – a compressor-type fridge draws about half that. An alternative is to run it via a 240V inverter, but you’ll still need plenty of electrical grunt.
Those who go off-roading over steep or uneven ground may find that absorption-type portable fridges don’t work very well en route, because these units operate optimally on a level, or almost level, surface.
As with a compressor-type fridge an absorption-type can function as a freezer, or a combination fridge/freezer. However, very high ambient temperature can upset the absorption-cycle efficiency.
An absorption-type portable fridge comes into its own when it’s required to operate for long periods, without generator or solar panel power supply. We’ve run an absorption-type portable fridge non-stop for around two weeks on one 9kg LPG gas bottle – and we could still tee-off gas supply to our LPG stove to grill some fish!.
Plusses: silent operation, three types of power input.
Minuses: slower ‘pull-down’ time; ambient and level critical; greater power draw.
Stowing your cooler
No matter what your choice of camping cooler, you need to make sure it’s safely stowed, so that it can’t move around or become a missile in the event of an accident.
It’s also important that you can access the contents and allow sufficient ariflow around the condenser plate for correct heat-exchange operation.
A fridge slide is a popular way of improving access, because the fridge can be slid out when entry is required. Another solution is a swing-and-slide frame that allows the fridge to be pulled out and then swung out of the way.
Often, a camping fridge is stowed high-up in the vehicle – usually on top of a set of storage drawers – making access to the lid impossible unless you pack a small step-ladder.
One alternative is a tilting slide, with a drop-down action that allows the fridge to tilt forward in the slide frame, improving access.
The Esky Turned 70
‘Esky’ is as much a household name as the ‘Hills Hoist’, ‘Victa’ and ‘Vegemite’ and has turned 60 years of age, but the brand goes back much further than most people think.
The first ice box sold under the trade mark Eskimo (Esky) was manufactured by Francis Malley’s household products company in 1884, but it wasn’t a portable unit.
Back then, houses had ice chests for refrigeration and the ‘ice man cameth’ with block-ice every day in a horse-drawn cart. (I can remember as a kid growing up in Sydney’s eastern suburbs, in the 1950s, jumping onto the back of the ice truck and sucking ice splinters while old mate did his house deliveries, carrying the ice blocks with scissor-shaped grapples.)
In 1952 Malleys launched a portable cooler, branded ‘Esky Auto Ice Box’. It was formed from sheet metal and had a wire handle that doubled as a lid clamp. The first portable Esky used cork sheeting for insulation, had room for six pint bottles and included a removable three-tray food rack. (I can remember my old man questioning the salesman closely about how many ‘long-neck’ bottles of Resch’s Dinner Ale it could hold.)
Aimed at motorists, the Esky was advertised in motoring publications with the claim that the product was: ‘just as essential in the boot as the jack’. The smiling Eskimo who became the familiar Esky brand character for the next 30 years made his first appearance near the end of 1959, with the catch-cry: “Cool, man, cool”.
Over the years the Esky cooler took on a new shape and new colours. By 1960, it was claimed that ‘500,000 happy picnickers’ were relying on their Eskys, but it took Malleys until 1961 to register the trade name ‘Esky’ for the portable food and drink container.
Although Australia views the portable Esky as a local invention this is a contentious claim, because of a 1951 American patent application that was formally granted in 1953. American leisure goods company Coleman produced its first US-market, portable cooler box in 1954.
Plastics manufacturer Nylex took over production of the Esky product range from Malleys in 1984 and in 1989 signed a licensing agreement with Coleman. Under the terms of this agreement Nylex manufactured Coleman coolers and Coleman sold the Esky brand to camping stores.
Unsurprisingly, after Nylex went into receivership in 2009, the Esky brand was acquired by Coleman.