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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 percent of the
battery nominal capacity.
For typical installations, a battery life of four
years or more would be expected.
The RCU battery management system
maximizes 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
percent of its capacity when 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.
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 can design and assemble
this cable as a value-added service, or the
utility can design and make their own using
the information provided in this section.
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 3 Vdc or 9 Vdc that
can supply up to 2 A continuous. This
supply is internally protected by current
limit from radio short circuits.
Supply direct from battery. In this case,
a 6 A 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 Auxiliary power
supply on page 30.
Serial interface
This is via the DB25 serial connector on the
electronics compartment. Use of these
signals is protocol dependent. Refer to the
relevant protocol manual for details. There
are two options for electrical signal levels:
1. RS232
2. 3 Vdc or 9 Vdc logic level with respect to
0 V (battery negative). The voltage is
configurable and applies to all signals.
The sense of each signal can be
configured separately (i.e., whether
voltage high signals logic true or false).
When using the serial interface, there is a
push-to-talk (PTT) clean contact for
operation of some radios (maximum current
0.5 A, maximum voltage 20 V). When using
the PTT output, there are configurable pre-
transmit and post-transmit times (0 – 10 s,
resolution 0.1 s).
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