Peltier-Electric Mini Fridge

The Peltier-Electric Mini Fridge appeared on the market around 2003 as a compact consumer item for cooling drinks and snackfoods at home and on the move. The 'mini fridge' came in a number of guises and sizes from product-branded and clasically stylised to the most basic and functional. Some designs are also offered as lids for standard 'cool-boxes' which would normally contain ice-packs.

All of these mini-fridges centre around the Peltier thermo-electric effect. The Peltier effect was discovered in 1834 by French physicist Jean Peltier who found that if an electric current is passed between dissimilar conductive materials in a circuit, heat will be transferred from one material to the other. A Peltier or 'Thermoelectric module' (TEM) is therefore a heatpump and can be used for both heating and cooling of an element.

The Pelteir Electric Mini Fridges found on the market today are mainly of plastic construction with a capacity between 9 and 24 litres and designed to be easily hand-portable. Due to the fact that most small TEMS run on 12v DC power, the Fridges usually have dual power input; one direct input at 12vdc from a car cigarette-lighter socket and also a 240v input which connects to an integral transformer to provide the neccesary power for the TEM. The benefit of this dual-power system is that the fridge can easily be used as a domestic installation or quickly unplugged and taken to an automobile to be used.

Description

Taking a Nikkai portable fridge as an example, we can look at what actually makes-up an average mini-fridge. The Nikkai example is a relatively compact 15 litre unit with a stylised handle and view-window. The unit has an integrated (although somewhat flimsy) carry-handle on top and is obviously intended to be portable. The front window which provides a narrow view of the stock within is 'double-glazed' in clear polycarbonate. Inside the unit, there is a door fixing for a can-holder (not supplied with this unit) and a removable shelf fitted halfway up. The cooling element is fitted near the top in the back-inside wall. At the rear of the unit, there are connections for both the supplied 12v car-adaptor and the 240v mains lead. Basic switches offer on/off control for either 12vdc or 240vac and the option to either cool or heat the fridge contents. There is a fan duct near the top (intake) and exhaust heat is vented at the side.

Technical

The Nikkai Fridge contains a single TEM at the upper rear of the unit. The TEM is fitted to a metal plate within the cooling compartment measuring approximately 65mm across. This in turn is mounted on an integrated plastic which is thermally conductive and covers the whole back and base of the cooling comparment. At the back, we have a 240vac to 12vac transformer/PSU providing power to the TEM and a 90mm fan. From the rear, the TEM is mounted to an aluminium heat-sink which receives airflow directly from the fan. Waste heat is then allowed to escape through a duct to the side. The outer casing of the cooling comparment including the door appears to contain (probably foam) insulation to reduce heat tranfer from outside-in.

Price	~£25-£65
Capacity	Approx 15 Litres
Weight	~3.5KG
Supply voltage	12vdc or 240vac

Are they any good?

Using TEMs as cooling system isn't really as effective as the classic pressurised heat-pump refridgerators on the market but it does have some benefits. The TEM based cooler is very compact and also lightweight. It is also mechanically very simple; the only moving part being the simple 12v fan. Unfortunately, the relatively small TEM can struggle if you're trying to cool items at a high ambient temperature. Best practice is usually to pre-cool your items in a regular domestic refridgerator before taking them to your mini-fridge, the mini-fridge is then quite capable of maintaining the items temperature. Due to the need to keep costs low and the fridges portable, the peltier mini-fridges on the consumer market are often quite flimsy.

Can you still buy a Peltier Electric Mini-Fridge?

Yes, you can find them on offer in many off-licenses and most 'gadget' retailers continue to stock them. Price is usually a function of capacity ranging from £25 up to £80 for the highest capacities.

Does the Museum of Interesting Tech have a Peltier Electric Mini Fridge in its real-life collection?

Yes, we have a Nikkai mini-fridge purchased from Maplin in 2004. The fridge is currently in active service providing a drinks cooling solution.