by Sol Jacobs, Tadiran Batteries
Not all battery chemistries are the same when it comes to powering devices designed for the IIoT. A few guidelines help field cells able to handle rugged surroundings for long periods.
The development of electricity in the late 1800s drove the first industrial revolution by providing abundant and inexpensive power to factories. This paradigm shift led to the development of innovative machines and processes that defined the modern workplace by boosting factory production.
Slightly more than a century later, a similar revolution is underway: the Industrial Internet of Things (IIoT). It is beginning to transform the modern workplace, bringing seamless connectivity to all types of industrial applications, including machine-to-machine (M2M) and system control and device automation (SCADA) technologies.
Unlike the past, however, the IIoT will not be bound by the limitations of the old-fashioned factory floor. A new generation of wireless technology extends the IIoT to places not currently served by the national power grid.
The main limitations of traditional electric power are proximity and expense, as it costs $100/ft or more to extend hard-wired ac power to any industrial setting. This cost becomes even more problematic with the logistical, regulatory, and permitting hurdles required to extend ac power to remote, inaccessible locations that are often environmentally sensitive as well.
The emerging IIoT will not be held back by the power grid. It will thrive on battery-operated sensors that extend Big Data analytics to all types of industries, including but not limited to transportation infrastructure, energy production, environmental monitoring, manufacturing, distribution, healthcare, smart buildings and industrial automation.
Industrial applications will need power supplies that can perform reliably even in extreme environmental conditions. This is especially true for applications characterized by complex, multi-tiered interoperability to synchronize manufacturing, supply chain logistics and product marketing.
Generally speaking, the more remote the application, the more likely the need for an industrial-grade lithium battery. Inexpensive consumer-grade batteries could suffice in certain instances, especially for easily accessible devices that operate within a moderate temperature range. However, inexpensive consumer-grade batteries can also be highly misleading: The cost of labor to replace a consumer-grade battery typically far exceeds that of the battery itself. For example, consider what it takes to replace batteries in a seismic monitoring system sitting on the ocean floor or in a stress sensor attached to a bridge abutment.
To judge whether a short-lived consumer-grade battery is a worthy investment, you must calculate the lifetime cost of the power supply. To be accurate, the calculation has to properly account for the cost of all labor and materials associated with future battery replacements.
Primary LiSOCl2 batteries predominate
Remote wireless sensors designed for long-term deployment are mainly powered by bobbin-type lithium thionyl chloride (LiSOCl2) batteries. These cells offer special performance attributes that are particularly well suited for devices that draw low average daily current.
Bobbin-type LiSOCl2 cells feature high energy density, high capacity and a wide temperature range. They also have a low annual self-discharge rate, with certain bobbin-type LiSOCl2 cells able to operate for up to 40 years. These features have made bobbin-type LiSOCl2 batteries the preferred power source for virtually all meter transmitter units (MTUs) in AMI/AMR metering for water and gas utilities.
MTUs are often buried in underground pits and see extreme temperatures that far exceed the limitations of consumer grade batteries. Extended battery life is essential to AMI/AMR applications because any large-scale system wide battery failure could create potential chaos by disrupting billing and customer service operations. To preempt this type of problem, utility companies specify bobbin-type LiSOCl2 batteries that have been field proven to operate maintenance-free for decades.
Bobbin-type LiSOCl2 batteries are also found in electronic toll tags, another early IIoT-related application. These batteries were chosen because they can handle the severe temperature cycles that characterize car interiors. Heat soak can hit 113° C (according to SAE) when parked, cooling down rapidly to room temperature. In cold weather, of course, the battery must handle cold soak and a rapid temperature rise.
This same battery technology is now being adapted to other transportation applications, such as MITE-WIS wireless data acquisition systems embedded within concrete repair patches in tunnels. These self-powered units monitor concrete sections to help detect problems in repairs that have been covered by a layer of high-temperature fireproofing. Bobbin-type LiSOCl2 batteries are also powering wireless sensors that monitor stress and vibration on critical bridge infrastructure. These battery-powered sensors often mount to the underside of bridge abutments, a location that cannot be accessed for routine maintenance without expensive scaffolding or safety harnesses. Batteries that can operate reliably for extended periods solve this problem.
The operating life of a bobbin-type LiSOCl2 cell can vary significantly depending on its annual energy usage and annual self-discharge rate. Most remote wireless devices use a low-power communication protocol to help extend battery life. In addition, these devices operate mainly in a “sleep” mode that draws little or no current, periodically querying for the presence of data and awakening only if certain pre-set data thresholds are exceeded. It is not uncommon for more energy to be lost through annual battery self-discharge than through actual battery use.
The way a battery is manufactured and the quality of its raw materials can significantly impact its annual self-discharge rate. For example, the highest quality bobbin-type LiSOCl2 cells feature a self-discharge rate as low as 0.7% annually. This means they retain nearly 70% of their original capacity after 40 years. By contrast, a lesser quality bobbin-type LiSOCl2 cell can have a self-discharge rate of up to 3% per year. So nearly 30% of available capacity is lost every 10 years from annual self-discharge.
High pulse requirements
Standard bobbin-type LiSOCl2 cells are not designed to deliver high pulses. This challenge can be overcome by combining a standard bobbin-type LiSOCl2 cell with a patented hybrid layer capacitor (HLC). The standard LiSOCl2 cell delivers the low background current needed to power the device during sleep mode. The HLC works like a rechargeable battery to store and deliver the high pulses needed to initiate data interrogation and transmission.
Alternatively, supercapacitors can be used to store high pulse energy in an electrostatic field. While in wide use for consumer products, supercapacitors are generally not recommended for industrial applications because of inherent limitations, such as the ability to provide only short-duration power linear discharge qualities that do not allow for use of all the available energy, low capacity, low energy density, and high annual self-discharge rates (up to 60% per year). Supercapacitors linked in series also require the use of cell-balancing circuits.
Bobbin-type LiSOCl2 batteries can handle the vast majority of long-life remote wireless applications. But there will be a growing number of IIoT-related applications that are well suited to be powered by energy harvesting devices, with Lithium-Ion (Li-Ion) rechargeable batteries used to store the harvested energy.
Several considerations go into the decision to deploy energy harvesting. Factors include the reliability of the device and its energy source; the expected operating life of the device; environmental parameters; size and weight restrictions; and the total cost of ownership.
Consumer-grade Li-Ion cells are candidates where the device is easily accessible and only operates for five years and 500 recharge cycles or less. They are also possibilities when the temperature range is a moderate 0 to 40° C. However, if the wireless device is slated for a remote site and could be exposed to extreme temperatures, the better choice is probably an industrial grade Li-Ion battery. These devices can operate up to 20 years and give 5,000 full recharge cycles, with an expanded temperature range of -40 to 85° C. They also can deliver high pulses (5 A for a AA-size cell). Industrial grade Li-Ion cells are ruggedly constructed with a hermetic seal, which is superior to the crimped seals found on consumer-grade rechargeable batteries, which may leak.
A prime example of industrial grade rechargeable Li-ion batteries in an IIoT-themed application is the IPS solar-powered parking meter. This networked meter offers multiple payment options (credit/debit card, contactless payment, and so forth), access to real-time data, and a web-based management system. It is also wireless, so it eliminates the overwhelming task of having to hard-wire millions of municipal parking meters.
IPS solar powered parking meters can connect with modules that read license plates and can notify authorities about outstanding parking violations. Built-in photovoltaic panels harvest and store the solar energy, charging industrial-grade rechargeable Li-Ion batteries. The batteries deliver enough energy to handle the high-current pulses that arise during data communications. The batteries also provide up to 20 years of 24/7/365 system reliability.
The next industrial revolution will be driven largely by electronic devices that are truly wireless, with bobbin-type LiSOCl2 cells and industrial grade Li-Ion rechargeable batteries combining to support technology convergence and interoperability. These long-term power supply solutions will power IIoT-connected wireless devices reliably and maintenance-free for decades.