Sustainable and Affordable
New ideas in wireless power can reduce our reliance on batteries to power the devices in the connected home. By: Ronald M. Weber, Global Industry Manager, Building Automation
Power. All of the electronic innovations that we use every day would be useless hunks of silicon, plastic and metal without it. The recent innovations around the Internet of Things are no exception. Every connected device, whether it is a fitness monitor on a wrist, a connected electronic door lock or an ultrasonic sensor in a piece of industrial machinery relies on power to function and connect to the rest of the world. As IoT becomes more pervasive in our lives, power management and delivery becomes a more and more of a challenge. Granted, there have been great strides in creating microprocessors that sip energy and components that use power measured in microwatts but they still need power. Sleep modes are regularly enabled in IoT devices to power them down so they consume barely measureable amounts of power but they still need power.
Despite all of the technological advances of late, no one has developed a perpetual power source so power delivery is near the top of designers challenges. In some instances where a convenient external power source is readily available, such as in industrial machinery, processing equipment, or even smoke detectors in newer homes, that simply means wiring the device to the power source using any multitude of separable connector options or quick-connect wire poke in terminations. In instances where a power source is not available, the designer is pretty much relegated to using batteries for power or utilizing energy harvesting devices such as photovoltaic cells or electrokinetic microgenerators.
Batteries are still the de facto power standard for most wireless electronic devices. These battery powered devices are now pervasive in our lives and will continue to expand as connected devices increase their presence in our day-to-day lives. The challenges a product designer of these designs faces will correspondingly grow as well. The designer needs to balance the size of the battery or batteries to the power they must provide and their anticipated life. This is not an easy or trivial task but do provide the IoT designer a stable, fixed form factor source of energy and a wide range of different sizes and integration options. Their global availability and standard sizes mean just about all consumers are very familiar with using and replacing them- whether it be a small LR1154 coin cell or AA (IEC R6) cylindrical battery. Regardless of which battery is selected, the designer has a number of different connector options available to simplify assembly, commissioning and later battery replacement.
Take a look at all the devices in a typical home and you can see how pervasive battery power has become. In applications such as our cell phones, we have grown accustomed to plugging in our phones at the end of the day to keep the rechargeable batteries topped off. We cannot imagine a television without a remote control powered by a couple disposable AA batteries. Everything from our flashlights to game controllers depend on batteries to function. Life-critical devices such as smoke detectors keep us safe in our homes and remind us of a failing battery by an annoying “chirp” that forces us to replace the battery. In the end, what this means is that to feed all these devices, every home has a stash of replacement batteries stored somewhere- never to be found when they are truly needed. Unless new ideas in device power are widely adopted or developed, the rise of home automation devices will dramatically increase the number of batteries required in the connected home.
Most new devices are wireless. These range from the small occupancy sensor hanging on a wall to wireless switches and key fobs to electronic door locks. In some applications, such as switches and key fobs, battery life is quite impressive often reaching 5 years or more on lithium-based coin cell batteries. In other applications with high current draws, such as electronic door locks and remote valves, practical battery life is measured in months rather than years. Due to practical and aesthetic reasons, these latter applications limit the types and quantity of batteries that can be used. In the case of the door lock, no one would purchase nor be happy with a door lock that takes four D-size (LR20) batteries to provide a five-year life so the designer needs to balance the practical aspects of the design against an acceptable battery life. The compromise typically means a pack of four to eight AA batteries to power the lock for up to a year until they need replacement. Most homeowners will mostly likely not complain too much about replacing door-lock batteries once a year – although in some instances, getting to the batteries often involves some disassembly of the lock. Homeowners are already accustomed to replacing the batteries in their smoke detectors annually so it is no big deal to replace a few more in door locks, right? Well, perhaps there is more to this. What if the owner is not a single home owner but a high rise apartment manager with hundreds of units or a facility manager for a university campus with thousands of dorm rooms with electronic locks? Suddenly, the simple matter of replacing batteries in a door lock becomes a very daunting, costly, and labor intensive task.
Continuing on the theme of electronic door locks, eliminating or minimizing the size and number of the batteries could have broad reaching effects. Suddenly, the size of the lock can be significantly reduced since the lockset no longer needs to accommodate a bulky battery pack and resulting in a much more aesthetic design. In a 1000 unit apartment complex with electronic locks and a one year replacement cycle, the ten-year cost of ownership of these electronic locks approaches $50,000 so there is significant cost savings potential for a solution to replace batteries in these locks. The challenge lies in the nature of electronic door locks. The electronic circuitry can be made to sip power in a manner similar to the key fobs or sensor modules found in homes. It is the small motors or solenoids used to activate the locks that draw significant current during activation and result in the biggest drain on batteries.
These door locks need to draw relatively high current when activated and only while the door is closed. This opens an opportunity to utilize an alternate, novel technology with the potential of completely eliminating the need for batteries. The technology is near-field power transfer. There are uses of this technology in consumer electronics now on the market, such as solutions used to charge cell phones or wearable devices.
Door-lock implementation requires mortising a small power transmitter into the door jamb and wiring it to a low-voltage DC source such as a doorbell transformer or similar source. A power receiver and conditioning circuitry is similarly mortised into the edge of the door so when door is closed, the transmitter and receiver line up to transfer up to 5W of power wirelessly across the door jamb gap. This amount of power is more than adequate to power most doors and can even be used to keep a small backup battery in the door lock assembly topped off in case of power failure.
Using wireless power techniques to power a door lock makes sense not just from a life cycle cost standpoint but probably more importantly from an ecological one as well. Using industry statistics on the installed global electronic door lock base and its anticipated growth over the next ten years, some startling numbers come to light. Given the need to replace 4 batteries in each lock every year will result in over 1.1 billion pounds of AA batteries deposited into landfills over the next ten years. This is the combined weight of five US Nimitz class aircraft carriers or 287,500 full size automobiles. There is no disagreement this is a staggering amount and when combined with the ecological impact of manufacturing these batteries, becomes a significant ecological concern. By adding wireless power into door locks, the need for using even a small quantity of disposable batteries is eliminated and could provide significant economic and ecological advantages. As we continue down the path to more automated homes and buildings, designers of connected devices for the home need to consider all available options for power, which may not necessarily be the ones that are the most convenient to design in. Designers need to carefully consider alternate power options, earlier in their design process, before defaulting to batteries. The result, for all of us, will be better designed products, with longer life cycles, that are easier and more cost-efficient to maintain, while enhancing the level of convenience these were developed to provide. After all, none of us want even one cargo ship carrier worth of disposable batteries dumped in our back yards.