Runtime Extension of Autonomous Sensors Using Battery-Capacitor Storage

Batteries are an important part in autonomous sensors power supply chain, so extracting all available energy is a determinant runtime affair. Autonomous sensors have a pulsed power consumption profile that causes high voltage drops in high impedance batteries. These voltage drops can make battery voltage go under the specified autonomous sensors´ voltage supply range leading to a runtime reduction from the ideal case. In this paper battery-capacitor hybrids are proposed to reduce voltage drops in autonomous sensors. Analytical expressions for the voltage transient behavior and runtime extension under pulsed loads have been presented. Minimal capacitor´s value for a determined voltage drop has been also obtained. Experimental results were carried out using two types of loads, a pulsed resistor and a real autonomous sensor. The runtime extensions achieved were 185 % and 169 % respectively. The ideal runtime (assuming no voltage drop) is nearly achieved in both cases, so almost all energy can be extracted.