10 tips for maximizing battery life
Tip #7 – Use efficient algorithms
The idea of using efficient algorithms is to get at the fact that the more time that is spent in a low power mode and a throttled back frequency, the longer the battery is going to last. Using algorithms that are fast and efficient will result in the system spending more time in power savings modes. Power savings modes use only a fraction of the current that they use when in full out tilt mode. Try to design the software and the system to do what needs to be done and then get into a low power mode. The result will hopefully not only be longer battery life but hopefully even a smaller, lighter cheaper battery!
Tip #8 – Watch for devices with high leakage current
When circuits are being designed, make sure that the leakage and quiescent currents are well understood. If necessary, prototype out the circuit and verify what the current draw of the circuit is. Things to watch for are devices with high standby currents and low valued pull-ups or pull-downs. Make sure that this information gets put into the battery budget!
Tip #9 – Select External Devices that can be turned off
During the hardware design when components are being selected, it can be extremely useful to select sensors and external components that have low power modes themselves or that can be switched off. External parts like EEPROMs, flash and sensors usually support low power modes. When they don’t, there are a couple of methods that can be used to disable them. One, is to design in a switch like a FET to turn power on and off for the device. One issue with this is that the engineer can’t forget that there is a diode drop of at least 0.3 volts and up to 0.7 volts which can affect the operation of the device. The second option is to use a regulator that includes an enable/disable pin.
Tip # 10 – Add a voltage and current monitor circuit to the device
Engineers rely on data in order to make design decisions. In many cases battery life optimizations are the last thing done on a project. All other features are implemented first and then before the product rolls off the production line the team scrambles to improve battery life. One of the best ways to understand the battery performance of the system is to include two simple circuits to monitor battery voltage and current. This information can then be logged and used to determine discharge/charge cycles, determine steady state currents and really understand how the system is operating from a power usage standpoint. Figure 3 and Figure 4 show an example battery voltage and current over the course of a single discharge cycle. Armed with this tool, the savings of each tip can be determined as it is implemented!
Figure 3 – Battery Voltage Discharge
Figure 4 – Battery Current Use
Using these tips, it is possible to tame even the unwieldy of power hogging devices. It important to keep in mind though that while these tips will decrease system power and improve operating efficiency, these tips need to be kept in mind during the design cycle and shouldn’t be thought of as a last ditch effort to get a product out the door. With a little luck, that new sensor design will have enough battery life to last a long time. Happy power savings!
Jacob Beningo is a lecturer and consultant on embedded system design. He works with companies to develop quality and robust products and overcome their embedded design challenges. Feel free to contact him at email@example.com, his website www.beningo.com or on twitter @Jacob_Beningo.
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