Powering automation and IIoT wirelessly
Industrial automation no longer is constrained to the factory floor. With the help of wireless communications and advanced lithium battery technology, the landscape is expanding rapidly to incorporate increasingly remote and hostile environments.
The explosion of wireless technology has fueled rapid expansion of the Industrial Internet of Things (IIoT), allowing billions of wireless devices to become seamlessly networked and integrated while being liberated from the power grid. Battery-powered devices have brought wireless connectivity to virtually all industrial sectors, including process control, asset management, machine-to-machine, systems and systems control and data automation, transportation infrastructure, energy production, environmental monitoring, manufacturing, distribution, health care, and smart buildings, to name a few.
Critical to this growth surge has been the evolution of low-power communications protocols, such as ZigBee, WirelessHART, and LoRa (a long range, low power wireless platform), and related technologies that permit two-way wireless communications while also extending battery life.
For example, the highway addressable remote transducer (HART) communications protocol has been providing a critical link between intelligent field instruments and host systems for decades, employing the same the caller ID technology found in analog telephony and operating via traditional 4-20 mA analog wiring. However, in the past, requirements for hard-wiring severely restricted the deployment of HART-enabled devices due to high initial expense, as it costs roughly $100 per foot to install any wired connection, even a basic electrical switch. This cost barrier becomes far more problematic in remote, environmentally sensitive locations, where complex logistical, regulatory, and permitting requirements cause expenses to skyrocket. Development of the WirelessHART protocol has eliminated all these constraints.
Choosing the ideal power source
The vast majority of remote wireless devices are powered by primary (non-rechargeable) lithium batteries. In addition, certain applications are well-suited to be powered by an energy harvesting device in conjunction with a rechargeable lithium-ion (Li-ion) battery to store the harvested energy.
The more remote the application, the more likely the need for industrial-grade lithium batteries. Inexpensive consumer-grade batteries may suffice if the device is easily accessible and operates within a moderate temperature range. However, the cost of replacing a consumer-grade battery can far exceed the price of the battery itself, causing the total cost of ownership to rise dramatically. For example, imagine having to replace a battery in a seismic monitoring system sitting on the ocean floor or in a stress sensor attached to a bridge abutment.
Specifying an industrial-grade battery involves multiple parameters, such as energy consumed in active mode (including the size, duration, and frequency of pulses); energy consumed in dormant mode (the base current); storage time (as normal self-discharge during storage diminishes capacity); thermal environments (including storage and in-field operation); equipment cutoff voltage (as battery capacity is exhausted, or in extreme temperatures, voltage can drop to a point too low for the sensor to operate); battery self-discharge rate (which can be higher than the current draw from average sensor use); and cost considerations. Industrial-grade lithium batteries most commonly are recommended for applications that demand the following:
- Reliability: The remote sensor is in a hard-to-reach location where battery replacement is difficult or impossible, and data links cannot be interrupted by bad batteries.
- Long operating life: The self-discharge rate of the battery can be more than the device usage of the battery, so initial battery capacity must be as high as possible.
- Wide operating temperatures: Especially critical for extremely hot or cold environments.
- Small size: When a small form factor is required, the battery’s energy density must be as high as possible.
- Voltage: Higher voltage requires fewer cells.
- Lifetime costs: Replacement costs over time must be taken into account.
Tradeoffs often are inevitable, so it is important to prioritize your list of desired battery performance attributes.
Choosing among primary lithium batteries
Lithium battery chemistry is preferred for long-term deployments due its intrinsic negative potential, which exceeds that of all other metals. Lithium is the lightest non-gaseous metal, and offers the highest specific energy (energy per unit weight) and energy density (energy per unit volume) of all available battery chemistries. Lithium cells, all of which use a non-aqueous electrolyte, with a normal operating current voltage ranging between 2.7 and 3.6 V. The absence of water allows lithium batteries to endure more extreme temperatures.
Numerous primary lithium chemistries are available including lithium iron disulfate (LiFeS2), lithium manganese dioxide (LiMnO2), lithium thionyl chloride (Li-SOCl2), and lithium metal oxide chemistry (see Table 1: Primary lithium chemistry comparisons).
Table 1: Primary lithium chemistry comparisons
|Li-SOCl2||Li-SOCl2||Li metal oxide||Li metal oxide||Alkaline||LiFeS2||LiMnO2|
|Primary cell||Bobbin-type with hybrid layer capacitor||Bobbin-type||Modified for high capacity||Modified for high power||Lithium iron disulfate||CR123A|
|Energy density (Wh/1)||1,420||1,420||370||185||600||650||650|
|Power||Very high||Low||Very high||Very high||Low||Low||Moderate|
|Voltage||3.6 to 3.9 V||3.6 V||4.1 V||4.1 V||1.5 V||1.5 V||3.0 V|
|Pulse amplitude||Excellent||Small||High||Very high||Low||Moderate||Moderate|
|Performance at elevated temperature||Excellent||Fair||Excellent||Excellent||Low||Moderate||Fair|
|Performance at low temperature||Excellent||Fair||Moderate||Excellent||Low||Moderate||Poor|
|Self-discharge rate||Very low||Very low||Very low||Very low||Very high||Moderate||High|
|Operative temperature||-67 to 185°F; can be extended to 221°F for a short time||-112 to 257°F||-49 to 185°F||-49 to 185°F||32 to 140°F||-4 to 140°F||32 to 140°F|
Source: Tadiran Batteries
Consumer grade LiFeS2 cells are relatively inexpensive, and can deliver the high pulses required to power a camera flash. These batteries have limitations, including a narrow temperature range of -4 to 140°F, a high annual self-discharge rate, and crimped seals that may leak.
LiMnO2 cells, including the popular CR123A, provide a space-saving solution for cameras and toys, as one 3-V LiMnO2 cell can replace two 1.5-V alkaline cells. LiMnO2 batteries can deliver moderate pulses, but suffer from low initial voltage, a narrow temperature range, a high self-discharge rate, and crimped seals.
Li-SOCl2 batteries are manufactured two ways: spirally wound or bobbin-type construction (see Figure 1). Of the two, bobbin-type Li-SOCl2 batteries are better suited for long-life applications that draw low average daily current, such as tank level monitoring, asset tracking, and environmental sensors that must endure extreme temperature cycling.
Bobbin-type Li-SOCl2 batteries feature the highest capacity and highest energy density of any lithium cell, along with an extremely low annual self-discharge rate-less than 1% per year, enabling certain cells to operate maintenance-free for up to 40 years. Bobbin-type Li-SOCl2 batteries also feature a glass-to-metal hermetic seal, and deliver the widest possible temperature range (-112 to 257°F).
A prime example is the medical cold chain, where wireless sensors are used monitor the transport of frozen pharmaceuticals, tissue samples, and transplant organs at carefully controlled temperatures as low as -112°F. Certain bobbin-type Li-SOCl2 batteries have been demonstrated to operate successfully under prolonged test conditions at -148°F, which far exceeds the maximum temperature range of alkaline cells and consumer-grade lithium batteries.
Bobbin-type Li-SOCl2 batteries also are deployed in virtually all meter transmitter units (MTUs) used in AMI/AMR metering applications for the water and gas utility industry. The extended battery life of a bobbin-type Li-SOCl2 cell is essential to AMI/AMR metering applications because large-scale system-wide battery failures can create potential chaos by disrupting billing and customer service operations. Bobbin-type Li-SOCl2 batteries installed in MTU units during the mid-1980s were tested nearly 30 years later and shown to have plenty of remaining available capacity.
Battery operating life is largely influenced by the cell’s annual energy usage along with its annual self-discharge rate. Battery operating life can be extended further by operating the device in a standby mode that draws little or no current, then periodically querying to data to awaken only if certain preset data thresholds are exceeded. If properly conserved, it is not uncommon for more energy to be lost through annual battery self-discharge than through actual battery use.
When specifying a bobbin-type Li-SOCl2 battery, be aware that actual operating life can vary significantly based on how the cell was manufactured and the quality of its raw materials. For example, the highest quality bobbin-type Li-SOCl2 cells can feature a self-discharge rate as low as 0.7% annually, thus retaining nearly 70% of their original capacity after 40 years. By contrast, a lesser quality bobbin-type Li-SOCl2 cell can have a self-discharge rate of up to 3% per year, causing nearly 30% of available capacity to be lost every 10 years due to annual self-discharge.
Though bobbin-type Li-SOCl2 batteries are not created equal, performance differences may not become apparent for years. Thus, due diligence is required when specifying a battery for long-term deployment in remote applications. Engineers must look beyond theoretical data to demand fully documented long-term test results along with actual performance data from the field.
Factoring in high-pulse requirements
Standard bobbin-type Li-SOCl2 cell are not designed to deliver high pulses, which can be overcome by combining a standard bobbin-type Li-SOCl2 cell with a patented hybrid layer capacitor (HLC). The standard Li-SOCl2 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 widely used in consumer products, supercapacitors generally are 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 that draw additional current.
Growth opportunities exist for energy harvesting
A growing number of industrial automation applications are deploying energy harvesting devices in conjunction with Li-ion rechargeable batteries. Photovoltaic cells are the most common form of energy harvesting, with equipment vibration and ambient RF/EM energy being used for niche applications.
Consumer-grade rechargeable Li-Ion cells can be used to store harvested energy if the device is easily accessible, requires a maximum service life of no more than five years and 500 recharge cycles, within a moderate temperature range (32°F to 104°F), and with no high pulse requirements.
Industrial grade energy harvesting applications typically demand a far more reliable power source, such as an industrial grade Li-Ion battery that can operate for up to 20 years and 5,000 full recharge cycles, with an expanded temperature range of -40°F to 185°F. These industrial grade cells also can deliver the high pulses (5 A for an AA-size cell) required for two-way wireless communications, and are more ruggedly constructed with a hermetic seal that is superior to the crimped seals found on consumer-grade rechargeable batteries, which may leak (see Table 2: Battery comparisons).
Table 2: Battery comparisons
|Maximum discharge rate||C-rate*||15C||1.6C|
|Maximum continuous discharge current||Amps||5||5|
|Power (-4°F)||W/liter||Greater than 630||Less than 170|
|Operating temperature||Deg. F||-40 to 194°F||-4 to 140°F|
|Charging temperature||Deg. F||-40 to 185°F||32 to 113°F|
|Self-discharge rate||Percent/year||Less than 5%||Less than 20%|
|Cycle rate||100% DoD||5,000||300|
|Cycle rate||75% DoD||6,250||400|
|Cycle rate||50% DoD||10,000||650|
|Operating life||Years||More than 20||Less than 5|
*C-rate is a measure of the rate at which a battery is being discharged. It is defined as the discharge current divided by the theoretical current draw under which the battery would deliver its nominal rated capacity in one hour.
Powering 50,000 heliostats
A prime example of an industrial grade energy harvesting application is the Ashilim power station in Israel, a futuristic solar power station that will use the sun’s energy to supply 121 MW of clean renewal energy, enough electricity to power more than 120,000 households, becoming the fifth largest facility of its kind in the world.
The Ashilim facility will feature 50,000 mirrors, called heliostats, which are controlled individually via wireless communications to actuate and control servo motors that allow each mirror to rotate and tilt precisely to concentrate energy toward a boiler that sits atop a tower. The concentrated solar energy boils water inside the tower to create high-temperature steam that powers conventional turbine engines that can produce up to 121 MW of electricity.
Each heliostat will be equipped with a small solar energy harvesting device along with a small battery pack consisting of six AA-size rechargeable Li-ion batteries. The rechargeable Li-ion battery will power the servo motors as well as power wireless communications to establish a mesh network that relays the data needed to synchronize the movement of all 50,000 mirrors. Making this application truly wireless eliminates the expense, complexity, and reliability concerns associated with installing and maintaining miles of wire and cable.
Three possible energy storage solutions were considered at the Ashilim project: industrial grade rechargeable Li-ion batteries, consumer grade Li-ion batteries, and supercapacitors.
Industrial grade Li-ion batteries were preferred over consumer grade Li-ion batteries because they served to reduce the total cost of ownership by eliminating the expense of having to change out all 50,000 consumer grade batteries every five years. In addition, the risk of a large-scale battery failure could severely compromise the reliability of the entire power grid, potentially impacting all 120,000 households and businesses.
Selecting an industrial grade Li-ion battery also made sense in light of the extreme environmental conditions of the desert, as these cells feature an extended temperature range (-40 to 185°F), and are more sturdily constructed.
Supercapacitors were also considered but not chosen for the Ashilim power facility. While popular for use in consumer applications, such as providing memory backup for mobile phones, laptops, and digital cameras, supercapacitors have inherent drawbacks that make them ill-suited for industrial applications. These drawbacks include short duration power, linear discharge characteristics that do not allow for use of all the available energy, low capacity, low energy density, very high self-discharge (up to 60% per year), and the need for cell balancing for supercapacitors linked in series. By comparison, industrial grade rechargeable Li-ion batteries offer:
- Higher practical capacity: 330 mAh (the equivalent pseudo capacitance is 1,200 F). A supercapacitor having the same volume has about 10 F max. (3.6 V).
- Lower self-discharge: 1 to 2 µA of self-discharge current compared to 20 to 50 µA of discharge current for a supercapacitor having about the same external volume.
- Higher number of cycles: AA-size industrial Li-ion cell can be charged and discharged for 35,000 cycles between 2.8 V and 3.9 V (80% depth of discharge [DoD]). The accumulated capacity during this study is approximately 8,750 Ah. This value is equivalent to: 8.750 x 3.6/10 F 9, equal to 3.2 million complete cycles for an equivalent sized AA-sized 10 F capacitor.
- Cell impedance: during 35,000 cycles, cell impedance increases by only 25% from initial value of 40 mOhm to 50 mOhm after 35,000 cycles.
- Low temperature performance: industrial Li-ion cells show excellent low temperature performance, with cell voltage that is significantly higher than that of a supercapacitor under a long or high current pulse
- A smaller footprint: Supercapacitors are much bulkier than comparable industrial grade Li-ion batteries (see Figure 2).
Powering municipal parking meters
In another IIoT application, industrial grade Li-ion batteries are being used in solar-powered parking meters, thus saving millions of dollars by eliminating the need to hard-wire many miles of metropolitan sidewalks (see Figure 3).
These wirelessly networked solar-powered parking meters offer state-of-the-art functionality, including multiple payment system options, access to real-time data, integration to vehicle detection sensors, and user guidance and enforcement modules, all linked to a comprehensive web-based management system.
Small photovoltaic panels gather solar energy, with industrial grade rechargeable Li-ion batteries used to store energy and to deliver the high pulses required for advanced, two-way wireless communications, thus ensuring 24/7/365 system reliability for up to 20 years.
Looking to the future
These case studies provide a glimpse into the future of industrial automation and the IIoT that will be driven increasingly by electronic devices that are truly wireless, with industrial grade lithium batteries providing long-term support for technology convergence and interoperability. Wireless devices now are able to operate maintenance-free for decades, with extended battery life translating into a higher return on investment (ROI) by reducing long-term maintenance expenses and by promoting greater environmental sustainability due to fewer battery replacements. [onlinebyline]
Sol Jacobs is vice president and general manager of Tadiran Batteries.
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