The work of modern efficient electronic devices dissipates a lot of heat, especially while overclocking. Effective work of such components require adequate cooling. As a rule, we use fan based coolers.

The reliability and performance of them grow constantly due to construction improving, usage of the latest technologies for sensor development. However, not so long ago there appeared new-based cooling devices - semiconductor coolers which utilize the Peltier effect.

Peltier refrigerators containing specific semiconductor thermo-electric modules have the widest perspective in the market for cooling devices.

Thanks to their unique heat and operational characteristics, Peltier modules allow to reach the required cooling of computer components without huge technical problems and finance expenditure. They are quite compact, convenient, reliable and efficient.

In the systems, elements of which are operated in the tough temperature modes (i.e. in case of overclocking), Peltier modules are of great interest.

Peltier modules

There used a so called thermoelectric refrigerator based on Peltier effect. The given effect was called after a french watchmaker (1785-1845.), who discovered it in 1834.

If you put a drop of water in the hollow on the joint of 2 semiconductors Sb and Bi, and switch on the current, the drop would freeze (with the reverse direction of the current the drop would melt ). This is how Peltier effect works.

Unlike the Joule heat which is proportional to the current strength squared (Q=R·I·I·t), the Peltier is proportional to the current strength and changes the sign (-/+) if the current changes the direction. The Peltier heat equals:

q=I·t, P is a Peltier factor that depends on contacting materials and temperature.

Peltier heat is considered positive in case of dissipation, and negative in case of absorption.

In this case the Joule heat in both calorimeters is the same (since R = R(Cu)+R(Bi)). But the Peltier heat differs in the sign. So, this experiment allows to calculate the Peltier factor.

In the table below you can see some Peltier factors for different pairs of metals.

Usually, a Peltier factor is calculated this way:

P - Peltier factor, a - Tomson factor, T - absolute temperature.

In theory, the Peltier effect is explained the following way: electrons speed up or slow down under the influence of contact potential difference. In the first case the kinetic energy of the electrons increases, and then, turns into heat. In the second case the kinetic energy decreases and the joint temperature falls down.

In case of usage of semiconductors of p- and n- types the effect becomes more vivid. On the scheme you can see how it works.

Combination of many pairs of p- and n-semiconductors allows to create cooling units - Peltier modules of relatively high power (see the scheme below).

A Peltier module consists of semiconductors mounted successively, which form p-n- and n-p-junctions. Each junction has a thermal contact with radiators. When switching on the current of the definite polarity, there forms a temperature difference between the radiators: one of them warms up and works as a heatsink, the other works as a refrigerator.

A typical module provides a temperature difference of several tens degrees Celsius. With forced cooling of the hot radiator, the second one can reach the temperatures below 0 Celsius. For more temperature difference the cascade connection is used.

The cooling devices based on Peltier modules are often called active Peltier refrigerators or Peltier coolers.

Peltier module's power depends on its size. The modules of low power might not be efficient enough. But the usage of the modules of too high power might cause moisture condensation, what is dangerous for electronic circuits. The distance between conductors on the modern printed circuit boards constitutes parts of a millimeter. Nevertheless, they were powerful Peltier modules and additional cooling systems which helped KryoTech and AMD companies to overclock AMD processors up to 1 GHz. We should notice here, that the systems work was stable and reliable enough. Similar experiments were made with Intel Celeron, Pentium II, Pentium III, which achieved tremendous performance growth.

We should point out that Peltier modules dissipates a lot of heat. That's why it's necessary to use not only a powerful fan in the cooler, but also other different fans inside the case.

The information on Peltier modules, refrigerators and their test results you can find on the following sites:

• www.melcor.com
• www.kryotech.com
• www.computernerd.com
• www.tomshardware.com

Operating features

Peltier modules are very reliable; they haven't got any moving parts, unlike refrigerators constructed according to the traditional technology.

But despite all the mentioned advantages, Peltier modules have some specific features, which must be taken into account when using as a part of a cooling unit. The most important characteristics are:

• The modules, dissipating much heat, require the relative fans and heatsinks which would manage to carry off the heat effectively. We should notice, that the thermoelectric modules have a quite low performance factor and they are themselves a powerful source of heat. The usage of these modules might cause overheating of the other components inside the system block. That's why it's necessary to install additional cooling systems inside the block. Besides, the modules consume a lot of energy, and in this connection a power supply unit capacity shouldn't be less that 250 W. Though there are sometimes Peltier refrigerators with its own power supply unit.
• In case of the module's failure the cooler becomes isolated from the cooled element. It might lead to fast overheating of the latter.
• Low temperatures might cause moisture condensation. This might lead to short circuits between the elements. That's why you should use the modules of the optimal power. Moisture condensation depends on the temperature inside the system block, the temperature of the cooled device and air moisture. The warmer air is and the more moisture is, the condensation is more probable. The table below shows the dependence between a condensation temperature on a cooled element and a temperature and moisture of the surrounding air.

The temperature of moisture condensation

Besides, you have to take into account some peculiar features when installing a cooler near a high efficient CPU of powerful computers.

The architecture of the modern processors and some system programs provide different power consumption modes depending on CPU load. Some people use "cooling" programs, i.e. CpuIdle, or Windows NT/2000 and Linux. In this case the usage of Peltier modules is undesirable, since it's assigned for continuous work. In case of low power supply of a processor, the crystal temperature falls much. This might lead to buzz. Remember, that theoretically Intel's Pentium II and Pentium III processors can't work at the temperature below +5°C (though in practice, they endure lower temperature).

Some more problems can occur in case your motherboard supports a function allowing to control the fan speed depending on the power consumption of the processor. In the regular conditions it improves the thermal mode of the processor. In case of Peltier module usage, you might face some problems. It takes place, since the module is a source of heat itself and thus, it requires the heat to be carried off.

Peltier modules can be used for cooling of videocard chips as well. The work of videochipsets causes huge amount of heat evolved, and it's at the same time quite stable.

It's quite rational to use intelligence systems to control not only fans but also thermoelectric modules. It will help to avoid both supercooling and moisture condensation.

Not so long ago the experiments on installation of the miniature modules in processors were carried out. It's considered to be a rather perspective way of processors' cooling.

The samples of Peltier coolers

Below you can see examples of thermoelectric coolers (TECs).

The active Peltier coolers from Computernerd

The PAX56B cooler is developed for Pentium and Pentium-MMX processors from Intel, Cyrix and AMD, working at the frequency up to 200 MHz. The thermo-electric module (30x30 mm) allows the temperature below 63°C at 25 W of dissipated power and the outer temperature of 25°C. It provides the lowest temperature than alternative fans and radiators. For normal work of this cooler it's necessary to provide 5 V and 1,5 A (maximum). The fan for this cooler require 12 V and 0,1 A (maximum). The fan parameters: ball-bearing, 47,5 mm, 65000 hours, 26 decibel. The whole size of the cooler is 25x25x28,7 mm. The guiding price is $35.

The PA6EXB cooler is developed for more powerful Pentium-MMX processors, dissipating heat up to 40 W. This cooler suits all processors from Intel, Cyrix and AMD intended for Socket 5 or Socket 7. The thermo-electric module (40x40 mm) consumes maximum 8 A (usually 3 A) and 5 V; the cooler uses a power supply unit of the computer. The whole size is 60x60x52,5 mm. For better performance it's necessary to provide at least 10 mm above and 2,5 mm on each side when installing the cooler. The cooler ensures the temperature of 62,7°C with 40 W of dissipated heat and the outer temperature of 45°C. To avoid moisture condensation and short circuits you should not use programs, which set a processor into a standby mode for a long time. The guiding price is $65.

The DT-P54A cooler (is known also as PA5B from Computernerd) is developed for Pentium processors. However, some companies recommend it also for Cyrix/IBM 6x86 and AMD K6. The radiator is quite small (29x29 mm). The cooler has a thermode to prevent overheating. It controls a Peltier element as well. The complete set includes an external control device (it controls voltage, a Peltier element, a fan and temperature). The device gives an alarm signal in case of failure of a Peltier element or a fan, the fan rotates at the speed less than 70% of the standard value (4500 RPM) or processor's temperature goes up more than 145°F (63°C). The Peltier element switches on at the temperature of the processor more than 100°F (38°C). Since the element is firmly connected with the radiator, you won't be able to install it on other one. The fan is quite reliable: 12 V, 4500 RPM, 6.0 CFM air supply speed, 1 W power input, 30 decibel. The price is $39 to $49.

The AC-P2 cooler is developed for Pentium II processors. The complete set includes 60 mm cooler, a radiator and 40 mm Peltier element. The cooler doesn't suit Pentium II of 400 MHz and higher, since SRAM chips practically don't get cold. The guiding price is $59.

The PAP2X3B cooler (fig. 8) is similar to AOC AC-P2. It has 2 more fans (60 mm). The same problems with SRAM cooling. You shouldn't better use it together with "cooling" programs, such as CpuIdle, and under Windows NT and Linux, since moisture condensation may occur. The guiding price is $79.

The STEP-UP-53X2 cooler is provided with 2 fans, which pump much air through the radiator. The guiding price is $79 (Pentium II), $69 (Celeron).

The coolers of Bcool series from Computernerd (PAP2CX3B-10 BCool PC-Peltier, PAP2CX3B-25 BCool-ER PC-Peltier, PAP2CX3B-10S, BCool-EST PC-Peltier) are developed for Pentium II and Celeron processors and have similar characteristics (see the table below).

The coolers of Bcool series

We should mention that the BCool group includes devices with similar features, but they lack for Peltier elements. These coolers are undoubtedly cheaper and not so effective.