RIM 1802G, Integrator Manual

Page: 48 / 76

Chapter 5: Power requirements
48 RIM OEM Radio Modem for GSM/GPRS Wireless Networks
Alkaline
You can also use rechargeable alkaline batteries. These cells are typically rated for about 25
discharge cycles, far fewer than NiCads, but they provide longer life than NiCads. For the first 5 to
10 cycles, you will receive about 70 to 80 percent of the battery life that you would expect from a
single-use alkaline cell. After 25 discharges, this number might drop to 50 percent.
Single-use batteries
Of the single-use cells, only alkaline and lithium cells provide the high current necessary for
transmission. However, AA alkaline cells are likely the best choice. They are inexpensive, widely
available, and provide an excellent power source. Alkaline cells typically run for approximately four
times longer than similar-size NiCad cells and for approximately three times longer than similar-
size NiMH cells.
Plug-in supplies
A plug-in supply converts normal AC power (usually 110V or 220V) into a steady DC source that
can be used instead of batteries. You must design your plug-in supply to make sure that voltage
spikes, lightning, and other power fluctuations cannot damage the radio modem. To keep the inputs
within the load limits of the radio modem, you can add zener diodes or other spike arrestor circuits
for transient voltage protection. These should have a value of 20V and be placed on the supply side
of the regulator circuit. Refer to "Load specifications" on page 46 for more information.
Automotive supplies
If you plan to power the RIM 1902G or RIM 1802G from an automotive supply, you must take steps
to protect the radio modem from the intense power fluctuations that occur when an automobile
starts. You should use a circuit that consists of inductors, transorbs and voltage regulators to make
sure that the radio modem is protected from these power fluctuations.
Commonly, in automotive applications, voltages can be as high as 70V, especially on startup.
Commercial automotive adapters are available that safely convert the 12V automotive supply to a
regulated supply suitable for operating the radio modem.
Warning: You must take precautions with alkaline rechargeable batteries. These cells are not intended to be
used to their full capacity, so their actual useful runtime is closer to 30 to 40 percent of a single-use alkaline cell,
and they require the user to pay closer attention to the battery state. If you fully discharge a rechargeable
alkaline battery, you may be able to recharge only a few times before the capacity decreases to the point where
it can no longer be used.
Warning: RIM strongly discourages the use of general-purpose carbon-based batteries; this type of battery
cannot supply the power required by the transmitter. You should recommend that users of your product use
single-use batteries that are clearly identified as alkaline.