Wireless onboard health monitoring devices are a promising preventive technology that can detect the early stages of bearing defects. However, the nature of the continuous monitoring requires an energy source sufficient to record and transmit data. Thermoelectric energy harvesting is an effective solution to power onboard wireless condition monitoring sensors during railroad operations. Thermoelectric Generators (TEGs) are considered to be environmentally safe, do not contain moving parts or complex structures, and require little maintenance. The TEGs play a crucial role in providing energy to run vibration and temperature sensors, as well as supporting LoRa communications. However, TEGs may be subjected to non-uniform temperature differentials caused by the forced convection generated by air motion relative to the vehicle when mounted on the railcar. It can be shown that non-homogeneous temperatures of two TEGs connected in series lead to reduced power output in comparison to the available power from each alone, and if the temperature difference of the underperforming TEG is lower than 41.4% of the other TEG, even less power than one TEG alone. This paper presents analysis and experimental data comparing several possible design solutions: (1) a simple series connection, (2) a series connection with bypass diodes, and (3) isolated TEGS with separate boost converters for each module.

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