10.4 Battery Life
The RCU uses a standard sealed lead acid (SLA) 12 V battery conforming to standards
JISC8702, 12 V, 7.2 Ah. This type of battery is readily available however battery quality varies
greatly by manufacturer and this affects battery life significantly. It is recommended to
purchase replacement batteries from Siemens.
In service, the battery life is affected by two factors:
The first is temperature, the higher the temperature the lower the battery life. This means
that at time of installation care should be taken to ensure that the RCU is on the shady side
of the power pole to reduce solar temperature rise.
The second is discharge/charge cycles of the kind found in solar powered systems. Each
charge/discharge cycle reduces battery life and the deeper the discharge the greater the
effect. This means that a solar system should be engineered to keep worst case overnight
discharge below 25 % of the battery nominal capacity.
For typical installations a battery life of 4 years or more would be expected.
The RCU battery management system maximises battery life by a three stage charging
method, temperature compensation and system shutdown if the battery nears exhaustion. The
period of backup available is related to:
The state of charge and capacity of the battery. At end of life the battery will have reduced
capacity, typically 60 % of its capacity at new.
The power consumption of the radio in receive or idle mode.
The power consumption of the radio in transmit mode and the transmit duty cycle.
The power consumption of the RCU electronic system which is typically <20 mA when a
serial data interface is employed and <120 mA when the Ethernet interface is employed.
10.5 Radio/Modem Interface Electrical
A cable (or cables) is required between the radio/modem and the RCU electronics
compartment to carry data signals and power. Siemens Service Centre can design and build
this cable as a value added service, or the utility can design and make their own using the
information provided in this section.
10.5.1 Power Supply
Power for the radio/modem is available on the DB25 serial connector on the electronics
compartment pin 6 (positive) and pins 1, 8, 9, 21 (negative/ground).
There are two options for power supply.
A regulated supply which can be configured between DC: 3 V and 9 V that can supply up
to 2A continuous. This supply is internally protected by current limit from radio short circuits.
Supply direct from battery. In this case a 6A fast fuse must be included in the radio cable
to protect the RCU from radio short circuits.
For details of how to set the power supply to the correct voltage refer to section 5.7.
There is the additional option to specify a “no-activity” time out period. If the RCU does not
receive data for the specified period of time, power to the modem is cycled.
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