Low Input Voltage DC-DC Converter for Energy Harvesting using Iron-Constantan Thermoelectric Cells

A thermoelectric generator (TEG) was constructed using a classical iron-constantan thermoelectric cells and a simple direct flame heating with an ethanol burner. Although modern TEGs based on bismuth-tellurium cells provide much higher voltage and efficiency, they are very sensitive to over-heating and cannot be used in applications with high temperature of the cell hot side ca. 400 – 500 °C at the simple direct flame heating. A series connection of 20 iron-constantan cells was used and the maximum provided no-load voltage is ca. 0.5 V at the average temperature difference between the hot and cold sides approx. 460°C. To increase the cell durability the burner is controlled to achieve a lower voltage (lower temperature) and the buck DC-DC converter self-startup at the no-load voltage of ca. 0.3 V is enabled. The construction of the whole TEG is described, the boost converter design with respect to its efficiency is proposed considering a very low input voltage and power. The solution of starting the converter at low input voltage without an additional supply source is presented. Efficiency map measurement is included.