Question

Sensor battery life and power problem.

A 1.5 V battery has a capacity of 600 mAh. It will be used in a sensor node with the Zigbee technique employed.

1.) Suppose that the total power used in the sensor node is 3 mW. How long can the battery last?

2.) When the sensor node is in the sleep mode, it will turn off the Zigbee transceiver and save 80% of total power consumption on the sensor. If the node can use sleep mode to keep the transceiver on for only 10% of the time, how long can the battery last?

Answer 1

1)

Given,

For battery: V = 1.5 V

Capacity = 600mAh

Battery Power = Voltage x capacity

= 1.5 x 600 mAh

= 900 mWh

Power used by sensor node = 3mW

Battery time = Battery power/ sensor power

= 900mWh/3mW

= 300h

2) Sensor saves power in sleep mode = 80%

Transceiver on for 10% of time only.

Sensor power uses in sleep mode = 20 % of 3mW

= 0.2 x3 mW

= 0.6 mW

Total power used by sensor = (0.9 x 0.6) + (0.1 x 3)

= 0.54 + 0.3

= 0.84 mW

Battery time = Battery Power / total power used by sensor

= 900mWh/0.84 mW

= 1071.43 h