Feature: Batteries
Accurate calculation of battery life By Brian Whitaker, Product Marketing Engineer, Keysight
B
attery life can contribute significantly to the cost and reliability of the Internet of Tings (IoT) infrastructure. While for consumer electronic
devices battery life is oſten a critical purchase consideration, the fact that the calculated battery life of IoT devices is oſten inaccurate is a significant problem for manufacturers. One way to measure battery life is to
divide the battery capacity in amp-hours by the average current drain in amps, which provides time in hours. However, in the real world this calculation is overly simplistic. In fact, the formula can generate inaccurate results because devices use different power modes like active, sleep and hibernate. Additionally, operating modes such as constant power and constant resistance will draw current from the battery differently and change the battery’s runtime. It is essential to fully understand how a battery responds to these different scenarios and the typical usage patterns of the device to accurately predict battery life.
22 June 2023
www.electronicsworld.co.uk In addition to varying current drain,
battery capacity is variable depending on the average discharge current and usage patterns. Further, temperature can affect battery life, another critical consideration. Other factors can lead to inaccurate
computed battery runtime compared to real-world usage, including: • Lack of accurate battery models and profiles;
• Battery profiles not generated with accurate device operating conditions;
• Inaccurate current consumption measurements;
• Voltage drops have not been considered; i.e., when the voltage reaches a cutoff range, the device shuts down. Battery emulation and profiling
soſtware can accurately predict battery life. Emulation soſtware also gives insight into the current drain, helping adjust device designs for longer battery runtime.
Profiling batteries Tere are several reasons why batteries should be profiled and characterised; for a start, it can help determine the amount of energy the battery can store
and supply as it discharges over time. Te open-circuit voltage and internal resistance vary as the battery discharges, so it’s crucial to map these out. Parameters that affect battery behaviour over its lifetime include temperature, load current profiles (constant/dynamic) and operating modes, like constant current, power and resistance. Some may ask, why use a battery
emulator instead of a battery for device testing? Tere are several reasons for this: • A safer test environment. An emulator does not require actual charging and discharging of batteries, which can become dangerous with repeated cycles.
• Repeatable results. Emulated battery results are more stable than testing a physical battery of which characteristics can fluctuate with repeated charging and discharging, and with varying results between batteries, even if they are the same model.
• Reduced test setup times. Te emulator will allow instant simulation of any state of charge (SoC), compared with having to wait while a physical battery drains to the desired level.
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