Figure 1
Battery-powered devices are redefining AMR/AMI metering, benefitting water utilities in many ways: by pinpointing leaks and detecting theft of services; reducing maintenance costs; improving billing and payment systems; enabling remote turn-on/shut-off, and more.
Achieving cost savings with AMR/AMI metering
The newest generation of ultrasonic AMR/AMI meter reading devices contain no moving parts so they can last indefinitely, limited only by the life of the battery. Common sense dictates that pairing a 20+ year MTU with a 10-year battery makes no economic sense as the use of a short-lived battery raises the cost of ownership. It also increases the risk of unexpected systemwide battery failures that can disrupt billing systems, compromise data, and overwhelm field service crews.
To achieve extended battery life, leading meter transmitter unit (MTU) manufacturers specify bobbin-type lithium thionyl chloride (LiSOCl2) batteries. This chemistry is preferred for its higher capacity and energy density, wider temperature range (-80°C to 125°C), and lower annual self-discharge rate (under 1% per year for certain cells). Extremely low self-discharge is achieved by harnessing the passivation effect, in which a thin film of lithium chloride (LiCl) forms around the anode of an inactive cell to impede the chemical reactions that cause self-discharge. Whenever a continuous load is applied, the passivation layer begins to dissipate, allowing energy to flow: a continually repeating process (Figure 1).
In addition to harnessing the passivation effect, battery self-discharge can also be affected by how the battery is manufactured, including the quality of the raw materials. As a result of all these factors, an inferior quality bobbin-type LiSOCl2 battery can lose up to 3% of its nominal capacity each year due to self-discharge, exhausting 30% of its total capacity every 10 years, making 20+-year battery life unachievable. Conversely, a superior quality bobbin-type LiSOCl2 battery can have a self-discharge rate of 0.7% per year, retaining 93% of its original capacity after 10 years, making 40-year battery life possible.
The extended service life of a bobbin-type LiSOCl2 battery was verified by Aclara (formerly Hexagram). While in the process of replacing meters that were installed in the mid-1980s, Aclara performed random tests and found that these older batteries had retained a significant amount of unused capacity even after 28+ years (Figure 2).
Figure 2
Smart solutions demand high pulse energy
High pulses of up to 15 A are required to power two-way wireless communications, which is required for enhanced data intelligence. To deliver these pulses, a standard bobbin-type LiSOCl2 cell is combined with a patented hybrid layer capacitor (HLC). The standard LiSOCl2 cell delivers low-level background current during ‘standby’ mode while the HLC delivers high pulses during ‘active’ mode to communicate data. The HLC also features a unique end-of-life voltage plateau, enabling ‘low battery’ status alerts for predictive maintenance (Figure 3).
Figure 3
Long-life battery performance cannot be easily simulated
Comparing batteries based on their self-discharge rate can be difficult as long-term performance cannot be effectively measured using short-term tests, which tend to underestimate the passivation effect as well as prolonged exposure to extreme temperatures. Therefore, utility managers must go the extra mile and conduct thorough due diligence when comparing AMI meter batteries.
Learn more here.
Sol Jacobs is VP and General Manager, Tadiran Batteries.
