The MTBF for standard TECs is at least 200,000 hrs, which is based on relatively stable running conditions, with several times ON/OFF per day during operation. However, in other applications, the power is frequently on/off, especially in constant temperature controller application. There is a test for research the influence of the on/off switch cycle to the TECs in a constant temperature. Install the TEC module with silicon grease between a couple of convector radiators. The load time of the current is 7.5s, and the breaking time is 7.5s, thus a cycle is 15s. During the cycle, monitor the input current of each TEC module. The mark for failure is that the resistance of TECs increases, resulting in the current decreases. The test takes about 25,000 hrs with at least 6 millions of cycles. Under this condition, the MTBF is 125,000 hrs, or 3*107 times of on/off switch cycle.
Most caloristat has a higher switch temperature difference, which can form an obvious thermal cycling. The temperature of TEC module will change between high and low temperature. Thermal cycling will definitely shorten the life span of TEC modules, therefore, it's not recommended to use traditional on/off switch constant temperature control system in the applications requiring high stability.
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