Siemens S5-135U/155U System Manual page 86

Central Controllers and Expansion Units Power Supply Units
Basic Functions
The power supply units offer the following functions:
The rechargeable battery (in the power supply) continues to back up while
either the lithium battery or external battery is being replaced or fails,
ensuring that no data are lost.
Monitoring The power supply units contain monitoring functions to detect the following
Functions
faults:
In this context, a voltage failure is equivalent to a drop of the monitored
voltage below a preset limit (see Section 4.3.6 of the Technical
Specifications).
Signaling
The failure of a monitored function is signaled by the power supply units:
Functions
4-20
System power supply
All the system voltages required for operation of the modules in a CC or
EU are supplied.
Power supply for backup (in the CC and EU 185):
A lithium battery or an external battery ensure data backup when the
system voltage is switched off or fails.
– The lithium battery remains in the CC/EU and ensures backup, even
during replacement of the power supply unit
– Instead of the lithium battery, an external battery can be connected for
data backup purposes. Situated on the front plate of the power supply
unit are two sockets to connect an external battery.
Heat removal
Three independent fans which are individually replaceable during
operation remove the dissipated power. If a fan fails, the supply voltage
for this fan is switched off and the other two fans continue operation at
increased speed.
Failure of system voltage
Failure of output voltages
Failure of an externally applied 24 V DC load voltage (voltage monitor)
Fan failure or inadequate air flow
Lithium battery failure
Rechargeable battery failure
via LED indicators on the front plate;
via relays with which signaling circuits can be switched;
via signals to the S5 bus.
System Manual
C79000-G8576-C199-06