What Is It?
The construction of a 12-volt cooler is similar to that of a standard picnic ice chest. The function of both units is to hold food or beverages at lower than ambient temperature. The main difference in the 12-volt cooler is the addition of an air intake port and a thermoelectric unit that acts much like the heat sink on a computer's central processing unit. Rather than adding ice to reduce the interior temperature of the box as in an ice chest, the 12-volt cooler reduces temperature by distributing the cooler air created by the thermoelectric plate with a fan ducted into the cooler's interior compartment.
How It Works
According to the on-line Encyclopedia Britannica, in 1834 French physicist Jean-Charles-Athanase Peltier discovered that when two copper wires are attached to a battery and joined by a length of bismuth wire, a temperature drop occurs at the junction where current passes from bismuth to copper and a temperature increase occurs where the current passes from copper to bismuth.
Modern thermoelectric units take advantage of this effect by bonding two plates of dissimilar semiconductors (commonly bismuth and telluride) to create a heat pump. One side of the unit will be heated by the Peltier effect, the other side will be cooled. Which side is cooled depends on the direction of the current. By placing aluminum fins on the unit to aid in distribution of the heat or cold produced and channeling the air into the insulated box, the storage temperature can be raised or lowered by 40 to 45 degrees F from ambient.
Manufacturers of 12-volt coolers take advantage of the potential reverse gradient by offering a heating cycle on most models. The heat cycle is achieved by switching the positive and negative poles on the power plug. Since the Peltier effect depends on the constant flow of electrons in one direction, only DC power can be used on these thermoelectric units.
How Good Is It?
Thermoelectric cooling is neither as efficient or as effective as the compression/evaporation cycle of refrigerators commonly seen in kitchens. While the freezer compartment of a kitchen refrigerator is commonly set to 0 degrees F, a thermoelectric cooler would need a room temperature of no more than 40 degrees to achieve the same result.
For portable applications, thermoelectric cooling offers the advantages of being simple and lightweight. The only moving part in the cooler is a fan to circulate air across the heat sink. Since it doesn't use a liquid refrigerant, there is no danger of losing cooling power due to a pressure leak.
You won't be able to make ice in a 12-volt cooler, but it's dependable and a lot easier to carry around than a refrigerator.
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