Low-power smart devices are being deployed worldwide to support applications ranging from SCADA to remote sensing, tank-level, flow and environmental monitoring, predictive maintenance programs and more. Applications that involve long-term deployments are predominantly powered by ultra-long-life primary (non-rechargeable) bobbin-type lithium thionyl chloride (LiSOCl 2 ) batteries, which are preferred for their exceptionally high capacity and energy density, wide temperature range, incredibly low self-discharge rate and superior performance in harsh environments. For example, Wavelet devices from Ayyeka use bobbin-type LiSOCl 2 batteries to power intelligent, AI-enhanced solutions that monitor hard infrastructure such as pipelines, control valves, flow meters, tank levels and more.
These devices are modular, scalable, flexible, autonomous, sensor-agnostic, military-grade TLS v1.3 encrypted and plug-and-play with no major coding skills required. Ultra-long-life bobbin-type LiSOCl 2 batteries deliver a reliable power supply without requiring access to the AC power grid.
Passivation: Key to extended life
Most low-power devices, including Wavelet, draw average current measurable in micro-Amps with pulses in the multi-Amp range, typically powered by primary (non-rechargeable) batteries. Certain niche applications draw higher amounts of average current measurable in milli-Amps with pulses in the multi-Amp range, typically powered by an energy harvesting device in combination with a lithium-ion (Li-ion) rechargeable battery to store the harvested energy. The battery’s self-discharge rate is a critical consideration, as chemical reactions draw current from a cell even when it is disconnected or in storage. The self-discharge rate can vary based on numerous factors, most importantly the passivation effect.
Passivation involves a thin film of lithium chloride (LiCl) that forms around the anode of an inactive LiSOCl 2 battery to limit its reactivity. Whenever a continuous load is applied, the passivation layer initially causes high resistance and a temporary drop in voltage until the discharge reaction begins to dissipate the LiCl layer: a process that repeats during prolonged periods of inactivity. The level of passivation fluctuates based on variables such as how the cell is manufactured, the quality of the raw materials, current capacity, length of time in storage, storage and discharge temperature, and prior discharge conditions, such as removing the load from a partially discharged cell increases the level of passivation, especially as the battery ages.
All batteries are not created equal
Standard bobbin-type LiSOCl 2 cells are uniquely capable of harnessing the passivation effect, but they cannot generate high pulses due to their low-rate design. A hybrid solution is to combine a standard bobbin-type LiSOCl 2 cell that delivers low-level background current during ‘standby’ mode with a patented hybrid layer capacitor (HLC) that delivers high pulses during ‘active’ mode, often to power bi-directional communications. The HLC features a unique end-of-life voltage plateau that can be interpreted to deliver ‘low battery’ status alerts that increase the accuracy of predictive maintenance programs.
Significant differences exist between the highest quality bobbin-type LiSOCl 2 cells with a self-discharge rate as low as 0.7% per year (able to last up to 40 years) versus inferior quality cells with a self-discharge rate of up to 3% per year (making 40-year battery life impossible). Unfortunately, it can take years for such quality differences to become fully measurable. As a result, due diligence is required when evaluating competing brands, thus requiring well-documented long-term test results along with real-life performance data from the field involving comparable devices operating under similar loads and environmental conditions. End-user testimonials are also extremely valuable.
A real-life example
Nationwide, the American Society of Civil Engineers (ASCE) estimates that 6 billion gallons of potable water are lost each day due to leaking pipes. Erie County, Pennsylvanie utilizes pressure-reducing valves to prevent leaking pipes and burst water mains across a 100-year-old system stretching 600 miles and serving over one million people. Wavelet devices are combined with Ayyeka’s Field Asset Intelligence software to deliver a comprehensive solution that continuously monitors pressure levels to identify potential ruptures and issue alerts via automated text messages, emails or cell phones. Ultra-long-life bobbin-type LiSOCl 2 batteries extend operating life to reduce long-term maintenance costs.
This piece was originally published in AUTOMATION 2024: 9th Annual Industrial Automation & Control Trends Report.
