The topic of battery performance and optimisation so that they, in effect, can run for longer, has become more important as battery-powered wireless devices in the IoT space have experienced their own growth. For applications anywhere from smart cities to environmental monitoring and wildfire detection, battery-powered sensors are being designed to operate for longer, with minimal manual intervention.
“It would be a lot simpler to list the IoT applications that don’t require batteries, because that’s going to be a shorter list,” as Brad Jolly, Technical Healthcare Specialist at Keysight Technologies put it in the latest episode of IoT Unplugged.
Tools for assessing battery performance
There is a “tension” between designing and testing devices, and their time to market, Jolly said.
“The good news is that there are a lot of tools that have been developed recently that will help developers to optimise the battery life, he explained. “A lot of the improvements that support improved battery life are available in low power chipsets that run at sub one volt power rails, and they consume very low power.” He also noted Bluetooth Low Energy (BLE) as a low-power protocol being implemented and electronic design automation software.
“There are a bunch of innovative and interesting test technologies that are available,” Jolly continued. “One example would be event-based power analysis, which allows engineers to correlate charge consumption with different device behaviours, such as RF communications and electronic events going on inside the device.”
This could be used by measuring current consumption over a certain period of time, depending on your needs, and then seeing how it responds to Bluetooth, data encryption and so on.
“Another example is a relatively new category of measurement device called a current waveform analyser that can measure extremely low currents with high bandwidth,” Jolly added. “Finally, there’s battery drain analysis tools and battery emulation systems that can really speed up the development of battery powered devices.”
Like any emulator, the emulation systems simulate the behaviours of a battery and can be invaluable for testing certain components.
“In addition to using these technological tools I think a lot of engineers are realising we can decrease time to market simply by learning from one another,” Jolly stressed, referring to published documentation on development.
Optimising batteries, not maximising them
The use of the word optimise rather than maximise was important, Jolly noted, because “maximising battery life is not always a good thing … When you’re engineering an IoT device you’re not trying to maximise battery life, you’re trying to optimise an overall combination of functionality and performance.”
“With BLE radios you can save energy by advertising at less frequent intervals or transmitting at lower power levels,” Jolly pointed out. “Will doing this lengthen battery life? It will. However, if you decrease the transmit power too much, then customers may not be able to communicate over the desired distances. And if you advertise infrequently, the customers may not find your device.”
This shows the balance engineers have to strike when designing their devices, and the due consideration that must be given to battery performance.
Jolly said it was important to distinguish between battery life versus batter run time. “Battery life is the length of time before you have to install a new battery, and battery run time is the length of time that a battery can properly power a device on a single charge,” he said.
Jolly said he saw these misconceptions all the time, but “I want to emphasise that these are the ways I use these terms, but different people will use the terms differently. It’s not a case of right or wrong. It’s just making sure you’re on the same page in the terminology you use.”
Noting the balance that must be struck, Jolly explained: “Sometimes in the quest for optimising one particular parameter, it can lead to suboptimal performance that degrades the overall experience … I’ll go back to the example of RF power. You can always crank down the RF power on your device to use less battery power that will extend the battery life. But does that mean you can’t communicate more than 50 feet? Or 100?”
Closing comments
Keep safety high on your list of priorities, Jolly stressed at the end of the episode. “The great thing about modern batteries is that they have a tremendous amount of energy stored in very small spaces,” he said. “The problem is that they have a tremendous amount of energy stored in very small spaces.”
And never stop learning, he said. “Every time I go to a battery conference, I end up with a ton of new knowledge. I go in thinking I know something and I walk out realising how much I still have to learn.”
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