ST, Micropelt demo thermoharvesting power supply

stmicropeltevalkitGeneva, Switzerland — STMicroelectronics and Micropelt GmbH (Freiburg, Germany) have announced a jointly-developed autonomous wireless sensor evaluation kit that combines thermal electrical harvesting with a solid-state thin-film battery.

The TE-Power NODE evaluation kit leverages Micropelt’s Thermogenerator and ST’s EnFilm solid-state thin-film battery as energy storage for power backup and pulse current. The power management and charge monitoring circuitry connect to the included graphical user interface software via a 2.4-GHz wireless link.

“Harvesting thermal energy holds enormous potential as a virtually infinite self-sustaining energy source, exploiting free surplus heat that would otherwise be wasted,” said Micropelt’s CEO, Fritz Volkert, in a statement. “As the world leader in power management, ST was the natural choice of partner to optimize the performance profile of our advanced thermoharvesting technology.”

At the heart of the new evaluation kit is the Thermoelectric Generator (TEG), which exploits a physical phenomenon known as the Seebeck Effect, in which electric power results from the heat flux produced by a temperature differential across a thermoelectric micro-structured layer, explains the company.

From an effective gradient of 10°C, the TEG generates a voltage of 1.4 V. Micropelt’s custom power conditioning converts this into sufficient power to drive the wireless sensor node and charge a battery using excess thermal energy, said Micropelt.

In the TE-Power NODE evaluation kit, the Micropelt TEG MPG-D751 is housed between a solid aluminum base plate and a finned heat sink. The base is attached to a suitable heat source, so the cooling effect of the heat sink can create a temperature differential across the embedded TEG.

The rechargeable battery used in the enhanced TE-Power NODE kit is ST’s EFL700A39 EnFilm thin-film solid-state battery, a 700-microamp-hour UL1642-certified rechargeable battery that can deliver high pulsed peak current (up to 10 mA) to provide power to the wireless sensor node during its communication with the network.

When the base plate of the evaluation kit is in contact with a heat source, the Micropelt TEG provides power to the system and recharges the EnFilm. When the heat source is removed, the TEG stops and only the EnFilm battery provides power to the wireless sensor. The combination of the TEG and EnFilm battery balances thermal supply gaps and establishes a virtually perpetual energy supply to the attached wireless system, say the companies.

The battery board, designed by ST, contains the EnFilm battery and the electronic circuitry that controls and monitors both battery charge level and the energy balance. The board includes a BiCMOS linear regulator (STLQ50) specifically designed for operating in environments with very low power consumption constraints, as well as the STC3100 battery management chip, which monitors battery voltage, current and temperature. The circuitry also incorporates a Coulomb counter to keep track of the charge/discharge status.

The wireless sensor module included in the evaluation kit was designed by Micropelt to establish a versatile ultra-low-power link to its graphical user interface, the TE-Power SCOPE. The software displays and logs thermal and electrical system parameters, including a continuously measured power balance between the TEG and the EnFilm battery.