A lowpower thermal chamber with a volume of only 2.5 liters capable of reaching temperatures over the 5ºC to 70ºC range was designed and constructed. Two small 12 V batteries are used as the power supply for the complete system. Thermoelectric modules were used as actuators since their size and performance characteristics allow the portability and precise temperature control. The PID control provided stability and errors better than normally found in expensive commercial thermal chambers, with maximum temperature error of ±0.2ºC with respect to the setpoint and with a fluctuation of ±0.1ºC. Thermal chamber, Thermoelectric modules, Stacked Thermoelectric modules, Analog PID, Temperature control, H Bridge Power Driver. I. INTRODUCTION OMMERCIALthermal chambers have a large volume, which makes them inappropriate for portable benchtop or field applications. The technology used in commercial thermal chambers employ compressors and radiators to cool down the chamber, requiring a lot of space and making them difficult to control with low steadystate temperature errors. To overcome these problems, this paper presents a technique where thermal electric modules (TEM) were used, making the equipment small and easier to control, resulting in a reduced size lightweight portable equipment that can be used in the field or in benchtop applications where precise temperature control are needed. II. DESIGN OF THE THERMAL CHAMBER The chamber size, insulation and materials are determinant in estimating the amount of power that will be required to cool or heat the chamber. The thermal chamber has the external Manuscript received October 9, 2007: Revised version received March 4, 2008. Anderson Spengler is with the School of Electrical and Computer Engineering FEEC/UNICAMP, 400 Albert Einstein Ave, 13083852 Campinas SP BRAZIL (email: spengler@demic.fee.unicamp.br). Elnatan C. Ferriera is with the School of Electrical and Computer Engineering FEEC/UNICAMP, 400 Albert Einstein Ave, 13083852 Campinas SP BRAZIL (email: elnatan@demic.fee.unicamp.br). J. A. Siqueira Dias is with the School of Electrical and Computer Engineering FEEC/UNICAMP, 400 Albert Einstein Ave, 13083852 Campinas SP BRAZIL (phone: +551935214901; fax: +551935214896, e mail: siqueira@demic.fee.unicamp.br). dimensions of 300 mm x 240 mm x 120 mm and the internal space is 240 mm x 180 mm x 60 mm (approximately 2.6 l). The insulation is made of an elastomer foam with thermal conductivity of 0.037 W/(m.K) at 20ºC, and its thickness is only 30 mm. To estimate the required power to cool the chamber, the AZTEC software [1] was used, and for the given dimensions and desired temperature, the program indicates that it is necessary 10.58 W, considering that an active internal load is dissipating 1W. Fig.1 – Actuators assembling diagram. An interesting feature of this design is that two TEMs are used in a series configuration, in order to reduce the temperature difference between the ceramic plates and, therefore, allow for higher heat transportation. The thermal chamber is built in two parts, which are united by a central element with two Teflon pieces in order to centralize the aluminum central parts. Fig.1 shows the block diagram of the structure, the position of TEMs, sensors and copper blocks. Since a critical part of TEM is dissipating the transported heat and the generated heat in this transportation, it was necessary to use a heat sink to remove the heat from the hot side of the top TEM. According to reference [2], the used heat sink will be 15º C above room temperature for a 125W load. The final assembling of the thermal chamber is done by fastening into the inner piece the module composed by the TEMs, copper blocks, heat sink, sensors and insulator. After this, the internal fan (required to make the spacial distribution A Low Power, Battery Operated Precision Portable Thermal Chamber with Double Thermoelectric Module Anderson W. Spengler, Elnatan C. Ferreira, and J. A. Siqueira Dias C INTERNATIONAL JOURNAL OF CIRCUITS, SYSTEMS AND SIGNAL PROCESSING Issue 6, Volume 5, 2011 627