Battery Size Matters

Five fundamental considerations for a battery-powered, wireless IoT sensor product.

 
 

Introduction

The Internet of Things (IoT) is upon us. Gartner recently reported a typical family home may contain more than 500 smart devices by 2022 (Gartner news, Sep 8, 2015). The promise is that every day home automation products will be smarter through the introduction of low-­cost IoT technology including wireless transceivers and innovative sensors. But these features take energy, and a majority of these devices will be powered by batteries.

This presents an interesting challenge. To successfully design a product for the connected home, designers must generally build a small form-factor product, with the cheapest bill of materials (BOM), and reliable operation over several years without battery replacement.

 
Dynamic Current used During One Polling Event Graph 
 
 
  ZigBee Wi-Fi Bluetooth Smart
Standards-based Yes (802.15.4) Yes (802.11) Yes
Standards Body ZigBee Alliance Wi-Fi Alliance Bluetooth SIG
Application Focus Monitoring & Control Web, Email, Video Sensors
Type of Battery Coin-cell Rechargeable (Li-ION) Coin-cell
Number of Nodes < 10 to 1,000 + < 10 to 250 < 10
Required Throughput (Kbps) < 250 > 500 < 250
Typical Range (Meters) 1 to 100 1 to 100 1 to 70
Network Topology Self-healing Mesh, Star, Point-to-Point Star, Point-to-Point Star, Point-to-Point
Optimized For Scalability, Low Power, Low Cost Ubiquity, High Throughput Ubiquity, Low Power, Low Cost

Table 1: Wireless Protocol Attributes

 
 
Type 2x AAA CR2032 CR123A CR2
Material Alkaline LiMnO2* Lithium Lithium
Voltage 3 V 3 V 3 V 3 V
Capacity 1000 mAh 225 mAh 1500 mAh 800 mAh
Diameter 10.5 mm (x2) 20 mm 17 mm 15.6 mm
Height 45 mm 3.2 mm 34 mm 27 mm
Weight 24 g 3 g 17 g 11 g

*Lithium Manganese Dioxide

Table 2: Battery Form Factors