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18
Battery backup
The battery provides backup power for the
RCU. The battery is of the lead-acid type
with a 12 V, 7.2 Ah rating. The battery is
protected by a fuse in the cable. If the
battery is accidentally reversed, the battery
fuse will blow but no damage will be done
to the RCU electronics. The battery cable is a
replaceable item in case it is damaged in
service.
Note that the battery negative terminal is
connected to the ground of the enclosure
and is also the 0 V signal for all the
electronic interfaces in the RCU.
The RCU maintains a digital point "Battery
Needs to be Replaced" (DPID 2), which
indicates that the battery is at end-of-life.
When this point is set, it lights the "Replace
Battery" LED on the RCU front panel and is
available for transmission via the SCADA
system. When the battery is replaced, refer
to Battery replacement section on page 57,
the point is reset and the LED is turned off.
The "Battery Needs to be Replaced" point
can be set in a number of ways:
Charging: While recharging the battery
after it has had a significant discharge
(for example, when the source has been
off for several hours), the total charge
put into the battery is monitored. If it
requires excessive charge (indicating the
battery is at end-of-life), the battery
replacement flag is set.
Discharging: When the source supply is
off, the battery is discharged to power
the RCU, both the electronics and the
SCADA radio. During discharging the
battery, voltage is monitored and the
time taken to drop to a level that
indicates 50 percent of the battery
charge has been consumed is measured.
If this time is too short, then it indicates
that the battery capacity is severely
reduced and the battery is at end-of-life
and the battery replacement flag is set.
This requires the radio average current
to be correctly configured, see the
relevant protocol manual for more
information.
Time in service: After a battery has been
replaced, the days it spends in service
are counted. When they exceed the
Battery Life configuration setting, refer
to RCU power supply settings on page
68, the battery replacement flag is set.
Radio power supply
The long-range radio/modem requires a
power supply to operate. The RCU provides
the following options:
A regulated supply which can be
configured between 3 Vdc and 9 Vdc.
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.
The supply is available on the serial-port
connector on the electronics compartment.
Refer to Radio/modem interface electrical on
page 65 for more information on the radio-
power interface.
Load-break switch power supply
The RCU incorporates a terminal to power
other devices not part of the RCU. This
capability is not normally used for FS
installations. If this terminal is shorted to
ground when the LBS switch is ON, the
battery fuse will blow but no damage will be
done to the RCU electronics.
The load-break switch has no use for Fusesaver
installations and should be turned OFF.
The terminal can be used to supply power to
other devices, refer to Siemens for
engineering support if this is required.
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