Specifications

Chapter 8
Power Supply
8.1 Introduction
Battery backup is required because of the poor reliability of the main power
supply on the island. Furthermore, if the device is to be powered from a solar
panel or wind generator, then the battery is required to sustain the device
when these are unable to supply power (i.e. at night or in calm conditions).
The battery backup is in the form of a 12V Sealed Lead Acid (SLA) battery.
This is chosen in favour of a lower voltage battery (3v6 LION or 6V SLA) as
a high voltage is required by the RFID module. The logic operates at 5V and
the GSM module at 3.8V. Thus, two independent power rails are required.
8.2 Power Requirements
Power requirements for the various modules of the GSM uplink circuit is
given in Table 8.1. Table 8.2 shows the power requirements for the RFID
system. It is important to bear in mind that the GSM module requires peak
currents of 1.9A (lasting a few microseconds and recurring with a frequency of
216Hz) and the power regulator should be specified accordingly (see Section
7.3.1 for further details of the GSM module).
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