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Wireless Sensor Battery Life, Power Management, and What to Do When Wireless Sensor Batteries Die

Keywords: Using Monnit Sensors, Battery Life, Power Management, Dead Batteries, Battery change, battery replacement,


Summary:

Average battery lifespan in a Monnit wireless sensor. Factors effecting battery life span. Tips to improve the lifespan of Monnit wireless sensors batteries. Understanding wireless sensor power management. Battery Change Notification.



The life span of the battery is dependent on a number of factors: how frequently the sensor transmits data (heartbeat), how far the sensor is from the wireless gateway and obstructions that could cause difficulty in sending data (farther distance and obstructions require that the radio to operate at longer intervals to send and receive data), the type of battery used (CR2032 vs AA), and the type of sensor of purchased.

Monnit estimates through normal usage a sensor in the field with a coin cell battery should last ~ 1-2 years, and a sensor with 2 AA batteries should last ~ 3-4 years before batteries need to be replaced. These estimates consider the following conditions:

  1. Frequency of Transmissions
    How frequently your wireless sensors transmit (heartbeat) can have a severe impact on the life of the battery. A Monnit wireless sensor with a standard coin cell battery transmitting once an hour will last approximately 2-4 years depending on environmental conditions. If you want to preserve the battery life of your wireless sensor, set the heartbeat (transmission interval) as high as your specific application will allow.

  2. Sensor Type
    In addition, not all sensor types use power from the battery in the same manner. Most of them do have similar current consumption characteristics, but there are exceptions. Sensor types that use more power than others include: Monnit Accelerometers (all profiles), Monnit Activity sensors (all profiles), Monnit Infrared Motion sensors. It is not unusual to see noticeable reduced battery life from these sensor types.

  3. Temperature Conditions
    Batteries are electrochemical devices which convert chemical energy into electrical energy. Extremes in temperature can cause the chemical characteristics of the battery to change, causing the battery to burn power faster when hot or not generate enough current when cold. In order to maximize the battery life of your wireless sensors, keep them as close to room temperature as possible (°60 F - °70 F).

  4. Radio Interference and Transmission Retries
    The radio transmission of your wireless sensors is a two part process. The sensor transmits its data to the Wireless Gateway Transceiver then listens for a reply transmission to acknowledge that the signal was received. When there is a significant amount of radio noise or interference, your wireless sensors may have to transmit longer in order to send and listen through the interference. If the signal is not received and acknowledged, the sensor will try to transmit again until it receives a successful response. Both of these issues can have an impact on battery life. Monnit wireless sensors operate on the 900MHz frequency that is less crowded than the popular 2.4GHz and higher frequencies, so you already should expect less interference using Monnit Wireless Sensors. To ensure optimal performance of your sensors and batteries, try to avoid areas that have an excess of radio interference from other devices.

  5. Handling
    The batteries are handled with care and do not undergo static electricity shocks or shorting of the positive/negative terminals.

Batteries are included with the purchase of every wireless sensor that ships from Monnit. Under normal operating conditions, a sensor in your Monnit wireless sensor network (WSN) will last for 3,000 transmissions (2-4 years with a 1+ hour heartbeat.) Here's a helpful battery life estimator. Monnit Battery Life Estimator Tool.

Q: What should I do with my wireless sensor when the battery dies?

A: With our standard sensors, once the coin cell battery has been depleted, you can change the battery by peeling the sticker away from the battery slot then use a paper clip or small screwdriver to push the battery out and replace with a new CR2032 coin cell battery. With AA battery type sensors, simply slide the battery compartment door open to access the batteries. We encourage you to recycle all old batteries.

Q: Will a wireless sensor notify me when I need to change the battery?

A: Each time the sensor transmits data to the iMonnit online sensor monitoring system it reports the battery power as well. Notifications can be set to alert you by email or text message, when a sensor's battery is about to expire.






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