You’ve heard it before: choosing the right battery for your Internet of things (IoT) device is critical for the success of your project. Not only will it ensure your device functions correctly for it’s whole lifetime, but it will also help reduce your time to market and optimize your total cost of ownership.
Batteries can be complex to understand, with varying elements: chemistry, technology, ability to match the application’s profile and power needs, temperature in the field…all have an impact on the behavior of the battery – and therefore of your device. A successful project requires anticipating and managing these elements effectively.
This article is intended to help IoT designers and developers choose and integrate a battery that best fits their IoT project, from defining the needed space in the device to evaluating the device’s lifetime in the field. As you evaluate the power needs of your application, a thoughtful approach will help you avoid common pitfalls.
Defining the size and location of the battery in the device without anticipating its power needs and the battery’s behavior in the application can lead to serious set backs. If the battery’s datasheet can provide you with some indications about the battery’s size and performance, the relevant information for IoT applications generally provided only shows specifications at a given temperature, for fresh cells, and,over a short period of time. For example, a Lithium Thionyle Chloride 3,6 V A size cell cannot deliver 100 mA pulse while maintaining constant voltage readings at 3,6V during 10 years, at various temperatures.
There is no “one size fits all” as the battery behavior will evolve over time and according to various parameters such as the frequency of data transmission or the temperature in the field of the application. Consequently, you might need to adapt the battery – and likewise the battery’s space – to meet your application’s needs.
What to do
Consider the energy and power needs of the application early in the design process. If the size of the device is your main concern, you may need to reconsider its environment, the consumption model (connectivity solution, frequency of data, time duration, current requested, and cut off voltage under which the device is out) or lifetime duration. If performance is your priority, make sure that the area available for the battery is sufficient to house a battery with enough power. To help you with this first approach, at early project stage, we have created a Smart Battery selector tool: in just 7 steps, it will help you discover which batteries match your use case, how much space you need to leave in your product design to accommodate them, an average estimation of their lifetime, and their price level. You can then edit the parameters of your application to find out in real time their impact on your battery choice.
As mentioned in the introduction, the behavior and lifetime of a battery are influenced by many parameters that can fluctuate over time such as the temperature of the application in the field, the storage conditions and duration, the rate of discharge, the chemistry that is being used... It cannot deliver constant current over its whole lifetime. As a result, it needs to be carefully considered by professionals who will be able to map out the battery’s behavior over its lifetime and make sure that it can deliver the power you need to make your application function correctly over its whole lifetime. That’s why we offer a free Product Specification Request (PSR) analysis to help our clients select the right battery.
What to do
Again, our Smart Battery Selector Tool can be a first step to help you understand how your application’s power requirements impact the battery’s choice and behavior. And if you are further into the project, we would recommend getting a free, personalized recommendation and lifetime calculation by one of Saft’s application engineer, whose role is to analyze your application’s operational profile and battery requirements to recommend the best, long lasting solution. They can also provide technical support and share their expertise on how best to optimize your applications. If you’d like to know more about what influences the battery operating time and how we calculate the battery’s lifetime, just click on the link.
One of the questions industrial IoT designers often have to grapple with is: why can’t an off-the-shelf consumer market solution be used in industrial design? This is how we sometimes see clients equipping their IoT solution with battery holders. Does it really make that much of a difference? The answer is a resounding “Yes.” The differences between industrial design and consumer design are often subtle but significant. Designing industrial products requires taking into account the support offered by the battery manufacturer during the whole life (from cradle to grave) of the battery: during design phase, industrialization, serial life (logistics support), after sales, and disposal of the battery.… Underestimating and/or not understanding what is unique about industrial application design can result in inadequate, less effective devices.
What to do
Again, it goes back to our first point: not only should you think about the battery early in the design process but also do not hesitate to get a personalized recommendation from our application engineers about how to optimize your electronic design. Our goal is to design the battery solutions that will last as long as your device is operating, without maintenance, to maximize your end-users’ value and benefits.
Because they are not aware of the parameters influencing the battery’s behavior, some of our clients come to us with partial or misconstrued information about their device. The temperature of the application —while stored or deployed in the field— may be not well determined, too large or too narrow compared to real world needs. Sometimes, the client does not know the device’s load profile of their application (pulses, environment, cut-off voltage…) may be mis-anticipated. And occasionally, it’s the standards (ATEX or security standards) applicable to their device that are unknown or misinterpreted.
What to do
Lao Tseu, a Chinese philosopher, founder of Taoïsm once said: “He who knows others is wise; he who knows himself is enlightened.” Ok, we’ll give it to you, it’s a bit far fetched, but you could apply this great quote to your design: knowing how batteries work is wise; knowing your application’s profile like the back of your hand and understanding its impact on your battery choice will ensure the success of your project. To help you gather the right information, we’ve explained in this article the process that our application engineers apply when making a battery recommendation and lifetime calculation. Don’t worry, we don’t expect you to become a chemistry expert over night, but having in mind some principles and more importantly, considering the battery as a key component of your IoT device, definitely helps.
The battery’s datasheet summarizes the performance and other characteristics of the battery in sufficient detail to allow the product designer or integrator to understand what can be expected of it. You’ll find information such as the chemistry used in the cell, the nominal voltage, the capacity, the energy density, the dimensions of the battery, and its discharge profile at various temperatures, and under various continuous current drains. Although this document is central to the choice of the battery, it can’t be taken at face value. For example, the pulse capability levels and maximum continuous current information indicated on the datasheet do not take into account your specific applications’ requirements. The curves resulting from laboratory testing are done under fixed temperatures, and with fresh cells, which means that the storage period before your device’s deployment is not taken into account for example, nor the temperatures variations. The voltage decreases over time, the pulse response is not stable and the battery could be affected by chemical reactions like passivation, a surface reaction that occurs spontaneously onto lithium metal surface in all primary Lithium batteries based on a liquid cathode technology, which varies according to the environment temperature.
What to do
It is essential that you confirm your choice with an expert who will be able to analyze your application’s specific power requirements and constraints and apply his/her experience in battery chemistry to recommend to you the best options to match your needs. It is also recommended to test your battery in conditions that are as close as possible to reality. Finally, and that’s also the subject of our next point, the battery can be stored several weeks in a warm environment prior to testing, to highlight the trends of its behavior over time. This will allow you to “age” the battery prematurely and then test the pulse capability of the battery. The values will not necessarily be exact but you’ll be able to detect the behavior of the battery once it is integrated into your device.
Testing a new device is a prerequisite and rare are the projects that see the light of day without having been subject to this routine. However, some tests don’t take into account parameters such as time and temperature. The tests are done over a few hours at 20°C and designers often expect the same behavior for their application in the field. A test in ambient temperature and over a short period of time cannot replace a real life test over several years. Some phenomenon can’t be modeled or accelerated which leaves too many unknown variables for an accelerated test to be conclusive.
What to do
You can apply the recommendations stated above and stock the battery in a warm environment to highlight an aging behavior and understand it over time, but nothing will replace a real life test of your application. Since you cannot obviously wait for 5 to 20 years before launching your device, our application engineers can help you evaluate as accurately as possible the performance of the battery in your device. They have seen, tested and recommended battery solutions for numerous and comparable applications and can apply their experience to your project.
Batteries are classed as dangerous goods and as such, need to be handled with care. Nonetheless, some IoT designers may not be aware that some regulations and certifications apply.
Transport for example is the object of a number of rules that must be adhered to. Batteries can’t be shipped to consumers without necessary labeling and protection.
Some devices, especially sensors, can be deployed in potentially explosive atmospheres and directives to protect employees from such risk in these areas need to be applied. These ATEX directives apply to all equipment intended for use in explosive atmospheres, whether electrical or mechanical, which means that batteries need to be certified for ATEX applications or fulfilled at least part 10.5 from the IEC60079-11 standard. The batteries within the equipment must also pass specific tests. In some cases, the casing needs to be completely hermetic to avoid spillage, etc.
Another directive that applies to batteries is the RoHS. This outlines the restrictions of the use of certain hazardous substances in electrical and electronic equipment — often referred to as the "lead-free directive”— that limits the use of certain substances such as lead or mercury.
You might also hear about REACH authorization procedure, the IEC60086-4 that regulates the battery nomenclature, or the UL1642 which are other certification standards for safety, etc.… and that’s not an exhaustive list!
Being aware of these regulations and choosing batteries that comply with them when necessary can avoid disappointment further down the line.
What to do
Make sure to find out about the regulations that apply to your device (or to the user or industry to which the device is intended) and that your chosen battery meets the necessary requirements. Over the years, Saft have developed batteries that comply with most of these regulations and if necessary, we can create bespoke solutions to match your needs. Regarding the transportation, this article will tell you everything you need to know before shipping lithium batteries or battery powered IoT devices.
And of course, our experts are available to help you in navigating all these regulations and certifications.
A natural reflex is to get quotes from various manufacturers and go for the cheapest option, in order to optimize the Total Cost of Ownership (TCO) of the application. But be warned, not all batteries are the same. The chemistry’s ingredients full list differs from one manufacturer to the other, as does the construction, the manufacturing process and the quality checks of the cells. Some batteries are less reliable and won’t be able to deliver the same current capabilities over time. Batteries that may initially seem the same won’t offer the same lifetime duration in your device. And a failing battery can cost dearly! (Loss of data, cost of replacement, etc.). As a result, the cheapest option might not be the most competitive one in the long run.
In addition, not all the manufacturers offer the same level of advice and experience.
What to do
Before making your choice, make sure you properly test the various battery options over a wide range of criteria and over a long period of time. Many of our customers decided upon Saft batteries after following such tests and because they received valuable help and advice from our application engineers, gleaned from our 100 years experience of battery manufacturing.
If you’d like to find out more, and how we can help you choosing the right battery for your IoT device, feel free to get in touch, or head over to our blog where you’ll find more information about batteries and IoT applications. You could also download our white paper about “How to successfully energize your IoT project?”.
We wish you all the luck and success in your adventure!
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