By Alix Paultre, contributing editor
One of the most discussed and stressed-over aspects of the latest revolution in portable, worn, autonomous, and remote electronics is the battery. The problem is that people pay both too much and not enough attention to it. They pay too much to the size, and less to the need, the capability, and the functionality.
Design engineers understand the importance of selecting the most optimized solution for their application, especially when the device has demanding power requirements. Selecting the right battery solution will directly affect the performance of the device and the experience for the end user. Understanding battery chemistry and cell selection as well as battery management systems will guide the proper battery selection and or design.
Size: Does it matter?
When it comes to energy storage, does the size of the battery matter? Actually, size isn’t as important as safety or operational reliability, among other things. Pure power isn’t necessarily the silver bullet to a design’s needs. It’s an easy out to address every range or operating time issue by adding a bigger or supplemental battery, and a brisk aftermarket in several application spaces exists to do just that. But it often isn’t enough.
The issue is being able to provide the energy that the system requires to fulfill the primary functionality for a reasonable time at a price point both acceptable to the consumer and able to generate a profit. However, in many cases, when designing a custom battery, size is a key driver. With device manufacturers, battery requirements are often an afterthought and an important component to ensuring that the design engineers can provide a battery supporting the mechanical requirements in the form factor that is needed.
We recently spoke to VARTA about the issues facing engineers developing products and battery choice. Arkadiy Niyazov, Project Manager at VARTA Microbattery, explained that for many engineers, it isn’t battery capacity as much as it is form factor and functionality. Arkadiy points out, “A custom battery pack often serves the customer better because it allows for an optimal solution for not only the power requirement but also safety and functionality.”
For example, in the rapidly-changing Li-ion battery industry, the traditional 18650 cell size is not the only choice. New options such as the 21700 and 26650 have now become more readily available, providing design engineers with more choices to meet the form, fit, and function needed to support the mechanical specifications of the end device while still delivering the energy required by the system.
When it comes to energy management today, it often isn’t how big the battery but how efficient the system it drives. In a hypothetical case of two identical batteries in two nearly identical IoT wearable medical systems, the one with better antenna matching will have a significantly longer battery life than that of the system less elegantly designed. Another example can be found in the coming wave of disruptive power electronics based on wide-bandgap semiconductors, with not only higher efficiencies but also higher power densities, smaller sizes, and reduced cooling requirements.
Buy or build?
One of the most fundamental questions in embedded design engineering is whether to procure subsystems off the shelf, custom-made, or do-it-yourself. In the case of modular subsystems like batteries, this can be a very difficult question to ask oneself. Not only are standard battery sizes readily available, they are a mature interface that has strong customer and industry support.
Providing a view from the field, Stefan Hald, Field Applications Engineer (Power Pack Solutions) at VARTA said, “I see a lot of requests from specialty spaces because they need to meet the redundant electrical and thermal safety and protection demanded by the application. The battery has to be as small as possible, but there also has to be redundancy and monitoring functionality included. We are also seeing a lot of requests for LED indicators for operational status, failure codes by blinking, and the like.”
Consumer products with a relatively large form factor have the hardest decision to make, as there is enough room to accommodate a standard battery without concerns of packaging or size compromises. This also applies to products that have evolved in form factors that already have accommodated themselves to legacy battery adoption.
One way to sidestep the issue is to do both, create a custom battery solution that also can work with off-the-shelf cells. Companies with the assets to do so usually do it for maximum market penetration while providing both an upgrade path for customers and an accessory sales channel to support it. Video game controllers and cameras come to mind, both high-use (high-power-drain) products with a customer base ranging from entry-level newbie to passionate professional. This is obviously not possible for every manufacturer, hence the difficulty of the decision.
On the “soft” side, multiple power options benefit both the manufacturer and consumer for marketing and practical reasons. Standard batteries are often the default choice unless there are form-factor concerns that preclude use of off-the-shelf batteries. Until recently, form-factor issues were the primary reasons that manufacturers went with a custom solution.
Often, user acceptance and form factor go hand in hand. A single thin removable battery appeals to the customer while also providing form factor and internal functionality to the manufacturer. For example, this 1,590-mAh VARTA EasyPack SLIM measures 5.2 mm max and has a CE Marking, a UL 2054 Listing, and IEC62133 Edition 2 compliance. This kind of solution is often the best of both worlds as it is a “standard custom” kind of solution that multiple products from multiple vendors can share.
Packing in functionality
The advantages of an optimized battery solution, however, can far outweigh the additional costs involved in designing a custom power pack into your product. As Stefan over at VARTA pointed out, the most popular add-on functionalities currently involve the battery itself, such as fuel gauging and safety monitoring. However, the ability to add functionality to a device by putting it in its battery pack lets designers provide features in a novel way that allows easy binning, scalability, and upgradability to the customer.
One of the biggest problems is the previously mentioned aftermarket add-on batteries. Many of these off-brand over-the-counter batteries have no security or safety technology integrated at all; there is often no way to tell if a store-bought battery is a real one from the manufacturer or just a tootsie roll wrapped in a label thrown together by scammers.
There are many stories of counterfeit bad batteries destroying products via agents from leaked acid to catastrophic thermal runaway (a fancy way to say, “It caught fire”). The first benefit of a custom pack is that you can add an RFID chip for inventory and counterfeit detection, a battery-monitoring IC to watch the charge state and thermals, or buy a chip that has both of those functionalities and more.
Once you open the battery pack to drop in a chip, your horizons broaden significantly. That chip could be a simple safety and security device, or it could be one of the new crops of IoT wireless ASICs, or it could be a complete SOC that lets you tailor your entire product line by the kind of battery pack it takes.
When designing a custom battery, design engineers need to understand cell technology for an application based on what is the best technical fit, which, in some cases, can have very demanding power requirements. Additionally, understanding cell technology trends will directly impact the direction for a particular design including availability of cells and new cell sizes such as Li-ion 26650 and 21700. Choosing the appropriate BMS is equally as important as they can have simple electronics to measure cell voltage or more complex BMS that affects the battery life and performance as well as ensuring safety.
Another example can be found in the area of robotics. Fig. 1 shows a VARTA battery pack that was created for a human robotics project that required advanced functionalities like fuel gauging and safety monitoring. The design included sophisticated casting to withstand the mechanical forces certification according to UL, a custom cell holder for production assembly and cell positioning, and highly customized PCM for electrical control, battery safety, and performance. Robots must not only operate remotely, they must be able to detect low-battery situations accurately and quickly enough to address them in real time either by reducing power needs or returning to base for recharge.
Fig. 1: This VARTA battery pack was created for a human robotics project.
Wireless functionality
The aforementioned wireless functionality can be implemented in many ways. Just integrating a cheap paper RFID tag in the label would go a long way toward reducing counterfeit risks as well as providing users with product information like pack capacity and may even give the device being powered a rudimentary interface to first-level battery functions like amount of charge and temperature.
In areas where there are options for the user such as near-field communication (NFC) payments, it is possible to add regional functionality to a device via the battery to address local or proprietary communication protocols. Many places are now accepting NFC pay, but some manufacturers may not wish to deploy that functionality across their entire product line. This also applies to internal security devices for internal company resources that may vary from location and facility.
The other major wireless functionality is wireless charging. Once thought of for longer-ranged applications, wireless charging is rapidly becoming a final-inch solution to eliminating batteries. Adding independent wireless-charging capability to your product’s battery pack delivers multiple benefits. Not only does this enable the user to buy multiple battery packs and charge the unused packs with the same wireless power interface, it allows the manufacturer to offer users of popular legacy products an upgrade path to wireless charging.
Optical functionality
When one thinks of batteries, lights usually come into the situation as loads. More often today, that light is an internal LED showing charge state. In the future, that LED could also transmit optical data, from troubleshooting information to augmented reality codes that would let users fight virtual dragons emanating from the back of their phones.
These embedded LEDs (or in the future, possibly OLED coatings) can also be used for aesthetic purposes as well as practical, or both. Status LEDs could be made to blink in time with music or other data (gaming) to enhance the smart-device experience, for example. The key is that once you open the box to adding a light, there is nothing restricting you to only one function for it, especially because most additional functionality can be added in code.
Looking forward
Electronic engineers have more and more choice when designing and specifying their battery packs, with more options for security and functionality than ever before. Understanding all of them (work with your supplier!) will help you greatly in achieving your product design goals.
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