Perhaps nowhere does the adage “time is money” apply more appropriately than with battery-powered remote wireless devices. Battery-powered devices provide an economical means for expanding the Industrial Internet of Things (IoT) beyond the electrical power grid to virtually anywhere at reasonably low cost. An example involves structural stress sensors that are attached to the underside of a bridge truss (Figure 1), where the cost of replacing the battery is exponentially higher than its initial expense, without considering the added safety risks.
In certain situations, battery replacement may be impossible. If the battery fails, it will result in permanent system failure, thereby causing a total loss of investment and compromised data integrity. An example is a seismometer placed on the ocean floor to detect earthquakes and warn of potential tsunamis.
It doesn’t pay to be “penny wise and pound foolish” when specifying a battery for a long-term deployment in a harsh environment. The challenge is to identify the battery that delivers the best overall value by delivering the required performance while minimizing the risk of premature battery failure. This is especially true for industrial applications such as asset tracking, supervisory control and data acquisition (SCADA), automated meter reading/advanced metering infrastructure (AMR/AMI), tank level and flow monitoring, environmental monitoring, machine-to-machine (M2M), artificial intelligence (AI) and wireless mesh networks, to name a few.
Reducing cost requires intelligent power management
Specifying a primary (non-rechargeable) battery for long-term deployment in a harsh environment can be a complex decision-making process requiring a solid understanding about the strengths and weaknesses of the various competing battery technologies.
Primary batteries power the vast majority of low-power devices that draw average current measurable in micro-Amps along with periodic high pulses in the multi-Amp range to support wireless communications. However, certain niche applications may require the use of an energy harvesting device in combination with an industrial grade rechargeable Lithium-ion (Li-ion) battery to store the harvested energy. These applications draw average current measurable in milli-Amps with pulses in the multi-Amp range, which may be enough to prematurely exhaust a primary battery.
To support energy harvesting applications, Highdrive lithium thionyl chloride battery Series rechargeable Lithium-ion (Li-ion) batteries that can last up to 20 years and 5,000 full recharge cycles while delivering high pulses along with the ability to be recharged and discharged at extremely cold temperatures.
Advantages of lithium-based chemistries
Numerous primary battery chemistries are available , the least expensive of which is the ubiquitous consumer grade alkaline chemistry. While renowned for delivering high rates of continuous current (i.e., powering a flashlight or a toy), alkaline chemistry involves numerous tradeoffs that make it inappropriate for use with most industrial applications, including a very high self-discharge rate (up to 60% per year) along with very low capacity and low energy density, which may require the use of additional cells that add size, bulk and expense. In addition, alkaline cells use a water-based chemistry that is more susceptible to freezing than lithium Primary cell
Lithium-based chemistries are far better suited for industrial applications. As the lightest non-gaseous metal, lithium offers an intrinsic negative potential that exceeds all other metals, resulting in the highest specific energy (energy per unit weight), highest energy density (energy per unit volume) and higher voltage (OCV) ranging from 2.7 V to 3.6 V. Lithium-based chemistries are also non-aqueous, thus less prone to freezing than alkaline cells.
Of the various lithium-based chemistries that are commercially available, bobbin-type lithium thionyl chloride (LiSOCl2) batteries (Figure 2) are overwhelmingly chosen for ultra-long-life applications. Bobbin-type LiSOCl2 chemistry stands apart for delivering the highest capacity, highest energy density and widest temperature range (-80°C to +125°C) of all. The highest quality bobbin-type LiSOCl2 cells feature a self-discharge rate of only 0.7% per year, thus enabling them to last up to 40 years. LiSOCl2 batteries can also be manufactured with a spiral wound design that delivers higher rates of energy flow with the tradeoff being a higher annual self-discharge rate.
Bobbin-type LiSOCl2 batteries are overwhelmingly preferred for long-term deployments at remote sites and extreme environments because they have higher capacity and higher energy density, among other attributes. Courtesy: Tadiran
The overall advantages of bobbin-type LiSOCl2 chemistry include:
Longer operating life of up to 40 years to lower the cost of ownership.
A wider temperature range of -80 to +125°C to survive extreme environments.
High energy density and capacity which could permit the use of fewer or smaller batteries.
Higher voltage which could permit the use of fewer batteries.
Bobbin-type LiSOCl2 batteries are marginally more expensive, so users need to determine whether the added performance is cost effective based on the potential long-term savings.
Harsh environments impact battery performance
A battery’s potential lifespan is initially dictated by its storage capacity, which is measured in Ampere-hours or Amp-hours (Ah). Based on the cell’s total capacity, its maximum run time can be estimated based on the average current being drawn. For example, a device consuming 1 mA of average current with a storage capacity of 1,200 mAh can have a maximum run time of 1,200 hours. However, such theoretical battery life is often far from reality, as actual performance can be negatively affected by factors such as prolonged exposure to extreme temperatures during storage and/or deployment, which can accelerate the annual self-discharge rate.
Self-discharge results from the chemical reactions that occur even when there is no connection between the battery’s electrodes or to any external circuit. As a result, many low-power devices consume more energy because of self-discharge than is required to operate the device.
Batteries are often refrigerated during storage to reduce their annual self-discharge rate by slowing down the electrochemical and diffusion reactions to reduce energy flow. However, prolonged exposure to extremely cold temperature should be avoided whenever possible. Likewise, prolonged expose to extreme heat can degrade battery performance by increasing chemical reactivity, which can lead to accelerated self-discharge, voltage delays and drops, power delays and the depletion of electrochemical constituents.
Other variables can also impact a battery’s self-discharge rate, including the peak current, consumption profile, temperature range, age of the cell and the leakage current drawn by individual components within the device, to name a few.
Passivation pays dividends
The principal reason why bobbin-type LiSOCl2 batteries deliver the lowest possible self-discharge rate is due to their unique ability to harness the passivation effect. In essence, passivation involves the formation of a thin film of lithium chloride (LiCl) on the surface of the anode, which then acts as a separation barrier from the electrode to limit the chemical reactions that cause self-discharge. Whenever a continuous current load is applied, the passivation layer initially causes higher resistance and a drop in voltage until the continuous discharge reaction causes the passivation layer to begin dissipating. Once a battery becomes inactive for an extended time, the passivation layer returns, requiring another round of de-passivation.
The level of passivation varies based on several factors, including the cell’s construction, its current discharge capacity, the length of time in storage, the storage and discharge temperature, as well as prior discharge conditions such as partially discharging a cell and then removing the load. While passivation is ideal for extending battery life, it must be carefully managed to avoid any over-restriction of energy flow.
Experienced battery manufacturers can maximize the passivation effect through proprietary cell construction techniques and by using higher quality raw materials. As a result, the highest quality bobbin-type LiSOCl2 batteries can feature a self-discharge rate of just 0.7% per year, able to retain 70% of their original capacity after 40 years. Conversely, lower quality bobbin-type LiSOCl2 cells can have a self-discharge rate of up to 3% per year, exhausting roughly 30% of their available capacity every 10 years because of self-discharge, making 40-year battery life impossible.
Understanding the power demand
Product designers use a variety of methods to minimize energy consumption, including the use of low-power chipsets and components, low-power communications protocols and other proprietary techniques. While these methods may be helpful in reducing energy consumption, they are typically dwarfed by the choice of battery.
Another important consideration is the cell’s ability to generate high pulses during “active” mode, as low-power devices often require pulses of up to 15 A to power bidirectional wireless communications. Standard bobbin-type LiSOCl2 cells are not designed to deliver such high pulses due to their low-rate design. This challenge can be easily overcome by incorporating a patented hybrid layer capacitor (HLC) (Figure 3).
Using this hybrid approach, the bobbin-type LiSOCl2 cell delivers low-level base current during “standby” mode while the HLC delivers high pulses during active mode. The HLC also features a unique end-of-life voltage plateau that can be interpreted to deliver money-saving “low battery” status alerts that extend battery operating life through predictive battery maintenance.
Bobbin-type liSOCl2 batteries can be combined with a patented hybrid layer capacitor (HLC) to deliver up to 40-year service life in harsh environments while delivering the high pulses required to power wireless communications. Courtesy: Tadiran
Supercapacitors perform a similar role by generating high pulses for consumer electronic devices. However, supercapacitors are ill-suited for most industrial applications due to numerous drawbacks, including short-duration power, linear discharge qualities that do not allow for the use of all available energy, low capacity, low energy density and very high self-discharge rates of up to 60% per year. When supercapacitors are linked in series, they require the use of expensive cell-balancing circuits that add bulk while draining additional current to further reduce their operating life. In certain instances, supercapacitors can be paired with bobbin-type LiSOCL2 cells to enhance voltage response.
When ultra-long battery life is essential, it pays to do your due diligence and invest in a higher quality battery that can reduce or eliminate the need for costly battery replacements over the expected lifetime of the device. Unfortunately, differentiating a superior grade battery from a lesser quality cell can be nearly impossible based on short-term test results, which tend to be highly inaccurate because the long-term effects of a higher self-discharge rate can take years to become fully measurable. The limitations of short-term testing can be further magnified by using relatively small sample sizes and by underestimating the passivation effect as well as prolonged exposure to extreme temperatures.
When extended battery life is essential, users must seek to verify the promotional claims of potential battery manufacturers. To properly uate competing brands, users should require fully documented and verifiable test reports. Also, request data measuring the long-term performance of actual batteries in the field that have been operating under similar loads and environmental conditions, both during storage and deployment. It is also highly recommended that you contact numerous customer references.
Since short-term test data tends to be highly inaccurate, Highdrive has amassed a huge and continually expanding database by monitoring long-term battery performance over decades under laboratory conditions. Highdrive also monitors the long-term performance of customer-supplied samples from the field that represent virtually all operating conditions. As an added benchmark, Tadiran performs long-term tests on competing battery brands.
Identifying the right battery is an application-specific decision. For example, if a battery life of 10-15 years is sufficient, then numerous chemistries could be considered. However, if the application calls for an ultra-long-life power supply that can last for up to 40 years, then your choice may be limited to bobbin-type LiSOCl2 chemistry.
Another important consideration is whether the battery is being used as the main power source or as a backup energy source. If the battery is serving as a backup power supply and could sit idle for extended periods, then you need to carefully consider the operating environment, the cell’s self-discharge rate and the need for fast battery response, where applicable.
Every application is unique, and numerous variables can affect battery performance, so it pays to consult with an experienced applications engineer who can review your operational profile to help identify the ideal power management solution: one that delivers the biggest bang for the buck by neither under- nor over-performing.
Post time: 2024-06-25 22:43:50
