## Tuesday, March 12, 2024

Stacking Cheap Peltier Modules - Lower than -40°C

In one of my physics projects, I tried to achieve the lowest possible temperature using simple means. For this I used a CPU cooler and so-called Peltier elements. But how do Peltier elements work?

In physics there is the so-called Seebeck effect, also known as the thermoelectric effect (wikipedia). If you have two different metal wires and bring the two soldering points to different temperatures, a so-called thermal voltage U is measured. This depends on the metal pairing and the temperature difference between the two soldering points. The following therefore applies: U = k * (T1 - T2).

As already mentioned, the factor k depends on the metal used. There is a thermoelectric voltage series in which the metals are ranked according to the voltage they produce. Logically, for the highest possible voltage, two metals are used that are as far apart as possible in the thermoelectric voltage series. But how can this effect be used for cooling? In physics, the principle of reversal often applies. As already mentioned, a temperature difference causes a thermoelectric voltage in the Seebeck effect.

Conversely, if a voltage U is applied to both ends, the two soldering points will have different temperatures. One point of release becomes hot, the other cold. This is the Peltier effect. This effect is used in so-called Peltier elements by providing a large number of soldering points and connecting one plate of the Peltier element to the cold soldering points and the other plate to the hot soldering points. If an electrical voltage U is applied to the Peltier element, a temperature difference between the two plates is obtained.

For this project you will need the following parts:

a powerful CPU cooler

several Peltier elements (you can get these cheaply on Amazon, ebay or aliexpress): link

a strong power supply, for example a converted computer power supply

a thermometer that can measure down to -200 °C (-328 degrees fahrenheit): link

I bought the CPU cooler from bequiet! cheap used. It has a heat dissipation capacity of 250 W. But even better would be a powerful water cooler from Corsair or a different brand.

In order to achieve the lowest possible temperature, a so-called Peltier stack is used. These are 3-4 Peltier elements arranged one above the other, with the warm underside of the upper Peltier element being cooled by the cold upper side of the lower Peltier element. The performance of the Peltier elements used should decrease towards the top. This is the only way the heat can be sufficiently dissipated. For this purpose, the Peltier elements are also operated with ever lower voltage.

I use a stack consisting of 4 Peltier elements, namely the model 0703 at the top operated with about 0.7V, below the model 3104 operated at 3.3V, then the 7108 with 5V and at the bottom a 12709 at 12V voltage. But here you can experiment according to your wishes and find out which combination can be used to achieve the lowest temperature. The electrical voltages of 3.3V, 5V and 12V are all provided by the converted PC power supply. Another controllable power pack is only required for the 0.7V of the uppermost Peltier element.

The lowest temperature I achieved was -64°C (= -83.2 degrees Fahrenheit). Of course it would have been nice if I had achieved -78.4°C (= -109 degrees fahrenheit). Because then I could even have made dry ice. But maybe one of you can do it.

By the way the lowest possible temperature is the absolute zero temperature at -273°C or 0 Kelvin. You can't go lower. Here is my simple instructable, how to determine this absolute zero temperature: instructable

Stacking Cheap Peltier Modules - Lower than -40°C

In one of my physics projects, I tried to achieve the lowest possible temperature using simple means. For this I used a CPU cooler and so-called Peltier elements. But how do Peltier elements work?

In physics there is the so-called Seebeck effect, also known as the thermoelectric effect (wikipedia). If you have two different metal wires and bring the two soldering points to different temperatures, a so-called thermal voltage U is measured. This depends on the metal pairing and the temperature difference between the two soldering points. The following therefore applies: U = k * (T1 - T2).

As already mentioned, the factor k depends on the metal used. There is a thermoelectric voltage series in which the metals are ranked according to the voltage they produce. Logically, for the highest possible voltage, two metals are used that are as far apart as possible in the thermoelectric voltage series. But how can this effect be used for cooling? In physics, the principle of reversal often applies. As already mentioned, a temperature difference causes a thermoelectric voltage in the Seebeck effect.

Conversely, if a voltage U is applied to both ends, the two soldering points will have different temperatures. One point of release becomes hot, the other cold. This is the Peltier effect. This effect is used in so-called Peltier elements by providing a large number of soldering points and connecting one plate of the Peltier element to the cold soldering points and the other plate to the hot soldering points. If an electrical voltage U is applied to the Peltier element, a temperature difference between the two plates is obtained.

For this project you will need the following parts:

a powerful CPU cooler

several Peltier elements (you can get these cheaply on Amazon, ebay or aliexpress): link

a strong power supply, for example a converted computer power supply

a thermometer that can measure down to -200 °C (-328 degrees fahrenheit): link

I bought the CPU cooler from bequiet! cheap used. It has a heat dissipation capacity of 250 W. But even better would be a powerful water cooler from Corsair or a different brand.

In order to achieve the lowest possible temperature, a so-called Peltier stack is used. These are 3-4 Peltier elements arranged one above the other, with the warm underside of the upper Peltier element being cooled by the cold upper side of the lower Peltier element. The performance of the Peltier elements used should decrease towards the top. This is the only way the heat can be sufficiently dissipated. For this purpose, the Peltier elements are also operated with ever lower voltage.

I use a stack consisting of 4 Peltier elements, namely the model 0703 at the top operated with about 0.7V, below the model 3104 operated at 3.3V, then the 7108 with 5V and at the bottom a 12709 at 12V voltage. But here you can experiment according to your wishes and find out which combination can be used to achieve the lowest temperature. The electrical voltages of 3.3V, 5V and 12V are all provided by the converted PC power supply. Another controllable power pack is only required for the 0.7V of the uppermost Peltier element.

The lowest temperature I achieved was -64°C (= -83.2 degrees Fahrenheit). Of course it would have been nice if I had achieved -78.4°C (= -109 degrees fahrenheit). Because then I could even have made dry ice. But maybe one of you can do it.

By the way the lowest possible temperature is the absolute zero temperature at -273°C or 0 Kelvin. You can't go lower. Here is my simple instructable, how to determine this absolute zero temperature: instructable