Designing Wireless Sensors to Last 25 Years
When designing a power management system for a wireless remote sensor, it is important to choose a primary battery that last for decades under extreme operating conditions. Lithium thionyl chloride chemistry is the preferred choice due to its proven ability to deliver 25-plus years of service life.
Optimizing battery life and long-term reliability involves numerous variables, including the chemistry, the cell design, the quality of mechanical components, the purity of raw materials and the manufacturing processes employed. Shortcuts in quality can negatively impact service life.
The total amount of active chemical ingredients and the ratio of each ingredient determine the cell’s nominal capacity. Predicting expected operating life solely on the cell’s nominal capacity can be misleading however, as the cell’s capacity is affected by the active components, the internal self-discharge, the application power profile and environmental factors. Since the volume of active ingredients is limited by the size of the cell, nominal capacity values often do not vary substantially. So the key differentiator often involves the inner structure of the cell and the ratio of active ingredients. For this reason, design engineers should evaluate the battery’s Equivalent Operating Capacity (EOC) to properly calculate its expected operating life, taking into account the cell’s self-discharge rate, application current profile and environmental conditions.
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