Supercapacitors in smart meters
Smart meters use long life high energy batteries but these batteries often cannot deliver the peak power required for data transmission. High power CAP-XX supercapacitors complement the battery providing the peak power needed for wireless data transmission.
Supercapacitors deliver peak power to support the battery and enable data transmission.
Water and gas meters are either too expensive or not safe to wire to mains power. They use a very high capacity primary battery, typically a Lithium Thionyl Chloride battery at 3.6V, with long life power the meter for 10 – 15 years. Narrow band cellular IoT, commonly used to report data, requires peak current in the range of 0.2A – 0.5A. Lithium Thionyl Chloride batteries have difficulty supplying this peak current suffering a drop of ~1V or more. This can result in the data transmission module suffering a brown out. This problem is worse at the sub zero temperatures of North American and European winters. CAP-XX supercapacitors have very low Equivalent Series Resistance (ESR) typically < 100mΩ, and high capacitance to store enough energy to supply the power required for the duration of data transmission. Hence, to supply 0.5A, the supercapacitor voltage drop will only be ~50mV. The battery only needs supply average current to the supercapacitor, which will be ~1mA or less. A dual cell supercapacitor module must be used across a 3.6V battery requiring cell balancing for reliable operation. Since the supercapcitor is permanently across the battery, leakage current and balancing current can be a significant drain on the battery. CAP-XX supercapacitor leakage current is very low at ~1µA/F, and the CAP-XX balancing circuit draws ~700nA. 1.7µA leakage + balancing current only draws 15mAh/year, or 0.1% of charge for a 15Ah battery.
For more details see Application Brief Supercapacitors in Smart Meters.