User's Manual

Boomer II User Manual & Integrator’s Guide _________________________________________________Installation
BM210012WT37 53 Copyright Wavenet Technology © November 2003
 Li-ion batteries are very sensitive to over-discharge and
represent a hazard if not properly designed with protection
circuitry.
 Typical charge method is constant-voltage, constant-current.
Applying Battery Technologies
When reviewing different battery technologies, consider the following
characteristics of OEM devices incorporating wireless data modems.
Current drain is not constant
Typically, battery manufacturers specify the battery discharge profiles
by assuming a constant-current drain model. In a wireless data system,
the constant current drain model no longer applies. There are three
levels of current drain contributions that can be expected: sleep,
receive, and transmit. The modem cycles through these different states
throughout the time it is powered on and in contact with the wireless
network. To determine the realistic battery life or capacity for your
product, you must contact the battery manufacturer or experiment by
transmitting for various durations.
Peak currents during transmissions
Since transmissions are typically short, the resultant current drain
during transmissions can be viewed as current pulses. These pulses
must be considered when selecting the proper battery technology, since
not all technologies are equally tolerant of current pulses.
Additionally, the internal impedance of the battery must be taken into
account at the peak currents during transmissions, since this is the time
when the largest voltage drop occurs across the battery terminals.
Adequate supply guard-band must be designed in to ensure that the
modem and any other circuitry in the final product are not reset during
transmissions.
Messaging model
To determine the required battery capacity for your product, you need
to define the messaging model for your target market. In regard to
battery selection, the messaging model details the following
information:
 Optimal number of hours per day of use prior to recharging the
battery
 Number of messages transmitted per hour
 Number of messages received per hour
 Average length of transmitted messages
Using this information and the typical current drains of the modem and
other circuitry present in your product, you can define the requirements
for battery supply voltage and capacity.