Wiring the S7-400
4-7
S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01
4.4 Choosing the Load Current Power Supply
Choosing the Load Current Power Supply
The input and output circuits (load current circuits) as well as sensors and
actuators are powered by the load current power supply. Listed in the following are
the characteristics of the load current power supplies required in special
applications for choosing the load current power supplies.
Characteristics of
the Load Current
Power Supply
Required for ... Remarks
Safe isolation Modules which must be
supplied with voltages v
60 VDC or v 25 VAC.
The Siemens SITOP power load current
supplies have this characteristic.
24 VDC load circuits
Tolerances of the
output voltages:
20.4 V to 28.8 V
40.8 V to 57.6 V
51 V to 72 V
24 VDC load circuits
48 VDC load circuits
60 VDC load circuits
If the output voltage tolerances are
exceeded, you should provide an energy
storage capacitor. Rating: 200 µF per 1 A
load current (with bridge rectification).
Load Current Power Supplies
The DC load current power supply must meet the following requirements:
Only a safe, isolated extra-low voltage of v 60 VDC may be used as the load
current supply. Isolation may be implemented according to the requirements of the
following, amongst other publications:
VDE 0100 Part 410 / HD 384-4-41 / IEC 364-4-41
(as a functional extra-low voltage with isolation) or
VDE 0805 / EN 60950 / IEC 950
(as a safety extra-low voltage SELV) or VDE 0106 Part 101.
Determining the Load Current
The required load current is governed by the total current of all sensors and
actuators connected to the outputs.
During a short-circuit, a current of two to three times the rated output current flows
briefly at DC outputs before the switched electronic short-circuit protection
becomes effective. When selecting the load current power supply, therefore, you
must ensure that the increased short-circuit current is available. With unregulated
load current power supplies, this excess current is generally ensured. With
regulated load current power supplies, particularly at low output levels (up to 20 A),
you must ensure a suitable excess current.
www.PLCworld.cn
To Next Page
Loading...
