Circuit model of a thermoelectric module for ac electrical measurements

Abstract

Measurements of assembled thermoelectric modules commonly include investigations of the module output power versus load resistance. Such measurements include non-ideal effects such as electrical and thermal contact resistances. Using an AC electrical measurement, a model for a thermoelectric module has been developed utilizing electrical circuits for both the thermal and electrical characteristics of the module. Measurements were taken over the frequency range of 1mHz to 500Hz using lock-in amplifiers. We present data showing the extraction of ZT from such measurements on commercially available modules. By knowing either the heat capacity of the module or the average module Seebeck coefficient, determination of the thermal conductance can also be achieved. The model proposed here provides a simple equivalent circuit which can be analyzed using an electrical simulator such as SPICE. This model makes use of the magnitude and phase of the electrical impedance measured by the lock-in amplifiers at the input terminals of the module and includes fitting parameters of the total electrical resistance, thermal conductance, heat capacitance, and module Seebeck coefficient.