Power Considerations - Siemens Simatic S7-200 System Manual

2.5

Power Considerations

The S7-200 base units have an internal power supply that provides power for the base unit,
the expansion modules, and other 24 VDC user power requirements. Use the following
information as a guide for determining how much power (or current) the base unit can
provide for your configuration.
Power Requirements
Each S7-200 CPU module supplies both 5 VDC and 24 VDC power:
Each CPU module has a 24 VDC sensor supply that can supply 24 VDC for local input
points or for relay coils on the expansion modules. If the power requirement for 24 VDC
exceeds the power budget of the CPU module, you can add an external 24 VDC power
supply to provide 24 VDC to the expansion modules.
The CPU module also provides 5 VDC power for the expansion modules when an
expansion module is connected. If the 5 VDC power requirements for expansion modules
exceeds the power budget of the CPU module, you must remove expansion modules
until the requirement is within the power budget.
Warning
!
Connecting an external 24 VDC power supply in parallel with the S7-200 DC Sensor
Supply can result in a conflict between the two supplies as each seeks to establish its own
preferred output voltage level.
The result of this conflict can be shortened lifetime or immediate failure of one or both
power supplies, with consequent unpredictable operation of the PLC system.
Unpredictable operation could result in death or serious injury to personnel, and/or
damage to equipment and property.
The S7-200 DC Sensor Supply and any external power supply should provide power to
different points. A single connection of the commons is allowed.
The data sheets in Appendix A provide information about the power budgets of the CPU
modules and the power requirements of the expansion modules.
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02
Installing an S7-200 Micro PLC
2-15