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Peltier module installation

 Installation of thermoelectric cooleres is a critical operation that determines operating capability and reliability of the device in general.

Since Peltier coolers contain a relatively fragile thermoelectric material and ceramics, they require careful handling and strict compliance with the installation rules. Failure to meet these rules may result in reduced thermoelectric module performance, lower life time or complete breakdown.

When installing thermoelectric modules, pay attention for the following recommendations:

  • Impacts, dropping of the module on a hard surface etc. may cause irreparable damage to the module.
  • When installing the module, make sure to prevent clamp screws from being excessively cross-threaded. Screws must be tightened stepwise, alternately and diagonally at opposite locations.
  • Clamp screws must have a spring element of any type (spring and dished washers).
  • Module surfaces must have a good thermal contact with the cooled object and heat-eliminating surface.

The thermoelectric module must not be used as a supporting element in the structure of the device in which it is installed. Nonflatness of mounting surfaces must not exceed 0.02 mm. Surfaces must be free from any type of foreign particles, including fat stains. If two or more Peltier modules are installed in the structure their location height difference must not exceed 0.01 mm. When installing modules, use thermal grease or thermal pads.

How to install thermoelectric module

Typically, thermoelectric coolers are installed in a device structure between heat-sinks that are in contact with the cold and hot sides. The diagram of this installation type is shown in Fig.1 and Fig.2.

Peltier cooler assembly 1

Peltier cooler assembly 2

 To install a thermostatic module using thermal grease, perform the following operations:

1. Check the quality of the surface on which a thermoelectric module is to be mounted. The surfaces of heat sinks must be clean and free from foreign particles and fat stains; its nonflatness and roughness must not exceed 0.02 mm.

2. Apply a continuous even layer of thermal grease of minimum thickness to the mounting surface of a hot heat sink. Carefully, applying no mechanical force, place the Peltier module with its hot side down on the prepared area of the hot heat sink. Carefully press the module down evenly to seat it on the heat sink surface and remove excess thermal grease from where the module contacts the heat sink.

3. Apply a thin layer of thermal paste to the proposed area of the thermoelectric module cold plate contact. Press the cold plate against the module surface.

4. Use the required number of screws to ensure a hold-down pressure of 13 to 15 kg/cmto keep the module to the heat conducting surfaces. Such pressure affords the minimum contact thermal resistance. Controlled pressure is insured by the use of torque wrench. Allow the assembled structure to stand for 1 hour. After this time expires check the hold-down pressure with torquing screws and adjust it to the requirements if necessary. Under the above conditions, ensure that thermal grease layer thickness is about 0.03 mm and thermal grease heat resistance varies between 0.03 and 0.05 °С/W. 

Thermal pads may be used as an alternative to thermal grease.

Thermal pads:

  • enable easy Peltier module assembly
  • have strictly uniform thickness
  • do not dry during long use
  • do not contaminate the surrounding components

In terms of heat-conducting properties, thermal pads are not inferior to thermal greases.

Calculation of Peltier module clamping force

Torque (Т) of the torque wrench may be calculated with the following formula:

T (torque) = (2.8 × 10-4 × p × d)/n, (kg × m)

where:
p is required clamping force (kg)
d is screw diameter (mm)
n is number of screws (2-4) used for module installation.

Example: Installation of a 40х40 mm module (e.g. ТМ-127-1.4-6.0М) requires a total hold-down force of 210 to 240 kg.

When two 4 mm screws are used to install a module, torque of 0.11 - 0.12 kg ×∙m must be set on the torquing screw.

When four 4 mm screws are used for the same purpose, torque must be reduced to 0.05 - 0.06 kg∙× m.

When designing products using thermoelectric modules and if thermal grease or thermal pads is used, it should be taken into account that heat losses result in temperature difference losses of 1.5 - 2.5 °С at the available capacity of 50 W.

To install a thermoelectric module using thermal pads, perform the following operations:

1. Check the quality of the surface on which a thermoelectric module is to be mounted. The surfaces of heat sinks must be clean and free from foreign particles and fat stains; its nonflatness and roughness must not exceed 0.02 mm.

2. Clean your workplace and remove foreign objects. Prepare thermal pads of required dimensions matching those of the thermoelectric module surfaces.

3. Remove protective film from the thermal pad. Without touching the working surface of the pad, place it on the module surface. Make sure the entire module surface is covered by the pad. Evenly press the pad to the module.

4. Repeat operation 3 for the other side of the module.

5. Install the module on the proposed contact area.

(Note: When using pads with protective film on both sides, remove the film from the pad outer side.)

6. Use the required number of screws to ensure a hold-down pressure of 13 to 15 kg/cmto keep the module to the heat conducting surfaces. Such pressure affords the minimum contact thermal resistance. Controlled pressure is insured by the use of torque wrench. Allow the assembled structure to stand for 1 hour. After this time expires check the hold-down pressure with torquing screws and adjust it to the requirements, if necessary.

 

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