Extended battery life is essential for hard- to-access locations.
By Sol Jacobs, VP & General Manager at Tadiran Batteries.
Low-power remote wireless devices are being deployed at remote sites and in harsh environments throughout the IIoT. These include applications like AMR/AMI metering, M2M, SCADA, tank-level and flow monitoring, asset tracking, and environmental sensors, to name a few.
Extended battery life is essential for hard-to-access locations where battery replacement is either prohibitively expensive or impossible. For instance, structural stress sensors mounted beneath a bridge truss are prohibitively expensive to replace, making it necessary to use extended life batteries. Another prime example is a seismometer placed on the ocean floor, where battery failure results in permanent system failure, causing a total loss of investment and compromised data integrity.
To save energy, most low-power devices operate mainly in a ‘standby’ state, drawing small amounts of average current measurable in micro-amps with pulses in the multi-amp range. These devices are predominantly powered by bobbin-type lithium thionyl chloride (LiSOCl2) batteries that deliver unique performance features. These features include extremely high capacity and energy density, an extended temperature range (–80 to 125°C) that is ideal for use in harsh environments, and— most importantly—an annual self-discharge rate of under 1% per year, which permits up to 40-year battery life.
Bobbin-type LiSOCl2 batteries achieve lower self-discharge rates due to their unique ability to harness the passivation effect. Passivation involves a thin film of lithium chloride (LiCl) that forms around the anode of an inactive battery to create a separation barrier from the cathode, thus limiting the chemical reactions that cause self-discharge. The passivation layer starts to dissipate when the device begins to draw continuous current, which is a continually repeating process.
Bobbin-type LiSOCl2 batteries are uniquely capable of harnessing the passivation effect, with the highest quality cells featuring a self-discharge rate as low as 0.7% per year, retaining roughly 70% of their original capacity after 40 years. By contrast, lower quality cells can have a self-discharge rate as high as 3% per year, losing 30% of their nominal capacity every 10 years, making 40-year battery life impossible.
Delivering high pulses
High pulses are required to power two-way wireless communications. Bobbin-type LiSOCl2 batteries cannot generate high pulses due to their low-rate design, thus requiring the use of a patented hybrid layer capacitor (HLC) to generate the high pulses. Utilizing this hybrid approach, the standard LiSOCl2 cell delivers low-level background current during ‘standby’ mode while the HLC generates high pulses during ‘active’ mode. The patented HLC also features an end-of-life voltage plateau that can be interpreted to broadcast low-battery status alerts for predictive maintenance programs.
Unfortunately, it can be difficult to compare competing battery brands as it can take years to properly distinguish ultra-long- life cells from those with higher self-discharge rates. As a result, thorough due diligence is required to ensure intelligent decision-making during
the specification process. Long-term testing is required, which is then verified by in-field data from comparable devices operating under similar power requirements and environmental conditions. For added validation, multiple customer references should be requested.
Investing in a higher quality battery pays long-term dividends by reducing your total cost of ownership, improving product reliability, and protecting data integrity.