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Maximizing your device’s battery life

Low power IOT devices, such as wearable devices, other types of portable products, and industrial monitoring devices that must be in remote locations, operate on batteries that are typically in the 3V to 4V range. At some point in the battery’s discharge cycle, the device will turn off due to the battery’s insufficient output voltage to power the device. To maximize the operating life of the product, it’s important for this low voltage, turn-off threshold to be accurately characterized. Since the device operates over a narrow and small voltage range, the source used to test and power the device needs to have good accuracy. This is especially important in determining the low voltage turn-off threshold.

One way to assess battery life is to use an actual battery to test the IoT device and determine the amount of time the device remained powered. That leads to two problems:

  1. Waiting for the battery to discharge can be very time consuming and delay development work.
  2. This test method is not precise, and specific test conditions are difficult to replicate.

A more ideal solution for testing your IoT device under the most realistic conditions is using a power source that simulates a battery. This solution allows you to test your design under a wide range of conditions from full battery charge to near complete discharge. If you need to select a battery type, then being able to simulate different types of batteries is essential.

Look for a battery simulator that does more than just simulate a battery’s internal resistance at a single point in time. Ideally, choose a battery simulator that can model the battery dynamically over its entire discharge cycle and uses a model that includes the state-of-charge and the amp-hour capacity, as well as the internal resistance.

 

The Keithley 2281S Battery Simulator and Precision DC Power Supply enable users to:

  • Set up a customized battery model and import it to the 2281S to simulate a real battery;
  • Set the battery state of SOC, Voc, and ESR at any value within their range before the test according to test requirements;
  • Modify the SOC, Voc, test mode, and I-limit during the test
  • Decrease the battery capacity to increase test efficiency

In addition, battery tests can be performed with the 2281S to measure capacity and resistance and to generate a battery model.

The 2281S can characterize rechargeable cell types only, as it carries this out during the charging cycle. For non-rechargeable cell types, we would utilize the Keithley 2450 or 2460 Graphical SourceMeter (SMU) instruments, a battery model-generating script operates the SMU instrument as a controlled current load and derives the model parameters required such as State of charge (SOC), Open Voltage (VOC) and Internal Resistance of the cell (or ESR). This is then exported via a USB memory stick into the 2281S.

Now that the battery profile has been created, the next step is to map out sleep and ramp up currents.

Characterizing the load current profile of a prototype device requires measuring the current in all of its operating states: sleep mode (from microamps to milliamps), standby modes (from hundreds of microamps to tens of milliamps), and all active states (from milliamps to amps) including short current bursts due to wireless transmissions.

The Keithley DMM7510 from Tektronix delivers a wide current measurement range, picoamp current sensitivity, high-speed sampling, and a 27 million reading memory buffer to measure and store a prototype device’s current profile.

Capturing these widely varying load current levels accurately demands an exceptional measurement solution that offers:

  • wide current measurement range from hundreds of nano-amps to amps
  • measurement speed to capture current pulses just a few microseconds wide
  • large memory buffer to store the prototype device’s current profile

Keithley 2281S-20-6 digital bench power supply, RS stock code (895-2388)

Keithley 2450 Sourcemeter, RS stock code (781-2964)

Keithley 2460 Sourcemeter, RS stock code (837-2145)

Keithley DMM7510 touchscreen bench digital multimeter, RS stock code (849-3832)

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25 Oct 2018, 8:49