Coolers - What You Get For Your Money
Cooler technology has come a long way since the dawn of the classic Coleman ice chest. Nowadays you can be 3 weeks into your camp-out at an isolated location in the middle of the summer and still enjoy ice cold beverages and ice cream treats...without using any ice at all. But this increase in cooling ability comes with a related increase in price, so let's look at the cooling options available to four wheelers and see how they stack up.
There are four main cooler types available to us. Here they are in order of cost:
How Things Get Cold
Understanding how the different coolers work is best done by first understanding how things get cool. Cooling relies on the principle of heat transfer. From Wikipedia: Heat transfer is the transition of thermal energy from a hotter object to a cooler object ("object" in this sense designating a complex collection of particles which is capable of storing energy in many different ways). When an object or fluid is at a different temperature than its surroundings or another object, transfer of thermal energy, also known as heat transfer, or heat exchange, occurs in such a way that the body and the surroundings reach thermal equilibrium. Heat transfer always occurs from a higher-temperature object to a cooler temperature one as described by the second law of thermodynamics or the Clausius statement. So for coolers, we always need a heat sink that will be cooler than the objects we want to make or keep cool.
This is the common cooler, basically an insulated box. The ice we place in it acts as the heat sink. The ice box has a lot going for it. It's cheap, rugged, lightweight, consumes no power (directly) and short of a severe structural failure, it will always function...as long as it has ice. That, of course, is its biggest limitation. Once the ice leaves the store's freezer, it begins absorbing heat and begins to melt. Put it in your cooler and it will continue to melt due to the warmer temperature of the items you add to the cooler, plus the heat transfer (slowed down, thanks to the insulation) with the outside environment. So while ice boxes work great for short periods, they aren't a good choice for long periods. During the summer, I don't think I've had a block of ice last more than 3 days under normal use (frequent opening and closing to retrieve cold drinks and adding warm drinks to be cooled down). The ice will last longer if you use a more heavily insulated cooler, such as the Coleman Extreme series, and if you minimize the frequency of openings, and avoid adding warm items to it. There's also the issue of the ice water making your food soggy, resulting in spoilage.
Of the no-ice coolers, these are the most common. They rely on the Peltier effect where passing a current through two dissimilar metals results in one absorbing the heat from the other. Aside from small fans (usually on both the inside and outside of the cooler), these coolers have no moving parts and are very reliable. There's also fairly affordable, starting at around $30 for a very small unit and then going up to $200 for larger coolers. Sounds great, but unfortunately their performance is quite mediocre. The best they can do is to make the inside about 20 C cooler than the ambient temperature, and they can't actually reach freezing temperatures. So if it's a sweltering 30C day, the absolute best that you could expect from this type of cooler is 10C which isn't cold enough for storing most perishables. The recommended refrigerator temperature for preserving perishables is 4C. It also takes them a very long time to cool things down. So while they typically use 5-10 amps, they are running ALL THE TIME. Your average vehicle battery would be drained if you left a thermo-electric cooler plugged-in overnight. You could leave it unplugged at night, but the cooling component will still conduct heat, allowing the cool air inside the cooler to draw in the ambient heat. In other words, when a thermo-electric cooler is left unpowered, it is an inefficient ice box. These coolers are best used when you use them to keep cold things cold, rather than using them to cool down warm things. Because they draw a fair amount of current, all the time, they're best used when your vehicle is running for long periods of time. They're great for road trips or when you're spending long days on the trail. For preserving food, they don't perform any better than an ice chest. For that role, I would put a block of ice in the cooler. The thermo-electric cooling during the day will do a good job of preserving the ice. At night, the ice will keep the cooler cold and can easily absorb enough heat to cool down any warm objects you add to the cooler.
These are typically called "3-way coolers" because they can run off of AC, DC or propane gas. They're most commonly used in RV applications, such as motor homes and trailers. These can get much cooler than the thermo-electric coolers and can actually freeze food. From the stand point of preserving food, absorption coolers are superior to the previous cooler types. They can achieve colder temperatures and hold them for long periods. When running off of 12V DC, they typically consume between 10-15 amps so it's not a good idea to run them overnight in this mode using your vehicle's battery. But they'll run much longer when attached to a propane tank, which is why they're so popular with the RV community. Performance varies by model. Some might only cool to 20C below ambient, while others might reach 40C below ambient. So check the specs carefully when shopping. (Tip: performance of an absorption fridge can be greatly improved by rigging up some small fans, like those found in computer cases, to cool the fridge's condenser.) Also, they need to be fairly level in order to function properly. They can be a bit fiddly compared to other coolers, but their performance/price ratio is quite good. They're a particularly good choice if you're going to be at camp for long periods of time. You could just set it up with a 20 lb propane tank sitting beside it and it should be good for a couple of weeks or more. Price-wise, they start at around $300.
This is the pinnacle of performance for portable cooling. Using the same cooling principles as your kitchen refrigerator, compressor coolers can freeze foods even on the hottest of days. The portable units are designed to run at angles of up to 30 degrees, and draw a modest 2-3 amps of power. Leaving them plugged into your vehicle's battery over night, or even for 2-3 nights is perfectly feasible. The disadvantage to these types of coolers is their price. $600 is the starting point. But if you can afford it, they're ideal for four wheelers. They're not finicky about their operating angle, they use very little power, and they make things cold without any problems whatsoever, ambient temperature be damned! They're typically equipped with a swing motor compressor, made by Sawafuji. It uses only a single moving part and is therefore very low-friction, light-weight, energy-efficient and reliable.
When it comes to preserving food, only three of them have merits worth considering. Thermo-electric doesn't perform well enough without ice yet comes with disadvantages (cost, power consumption and poor insulation). So if your budget only extends to thermo-electric, I suggest putting your money on a well-insulated ice box.
On paper, the portable 3-way or absorption coolers seem like the most versatile and offer a good compromise between price and performance. But they have some drawbacks which might explain why they're not very popular. First, it takes a while for the absorption system to start working, so it usually takes a couple of hours for them to get cold. Secondly, the ammonia and hydrogen gas used in the system is quite caustic, resulting in the system corroding from the inside out. These fridges tend to last not much more than 10 years. In contrast, compressor refrigerator systems can easily operate 20 years or longer (consider the household refrigerators you're familiar with). For a base-camp setup, or off-the-grid cabin, an absorption fridge is great. It's very reliable (few moving parts) and its simplicity makes it easy to manufacture. Powering it with propane gives you a compact power source that will last for long periods of time. Just be aware that the system will corrode and be prepared to pony up for a replacement after 10 years.
If you've got deep pockets, the compressor cooler is the way to go. It can hit the low temperatures, it gets cold quickly, it can operate at extreme angles (up to 30 degrees) and it has a very modest power draw.
How To Afford A Compressor Cooler
As I mentioned earlier, compressor coolers start at around $600. That's a big chunk of change and it would buy a LOT of ice. But in the course of my own search for a compressor cooler, I've found that these coolers are much more common among boaters and RVers than four-wheelers. They're also viewed as less of a luxury and more of a necessity, so when they show up on Craigslist, they don't ask nearly as much for them in the boating section, as they would for an ARB cooler in the 4x4 section. If you want to save some money and search for a used cooler, check the boating forums and look for phrases like "marine fridge" or "boat freezer" or some variation on that. Just make sure it runs off of 12V DC power. Brand names typically associated with compressor coolers are Engel, Norcold, Nova Kool and Dometic. Portable, highly efficient 12v compressor coolers are also used for transporting medical supplies and preserving them in remote areas. So you might also consider keeping an eye on government auctions.
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