Siemens SIMATIC S7-1200 - Page 1557

Calculating a power budget
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
1557
The CPU in this example provides sufficient 5 V DC current for the SMs, but does not
provide enough 24 V DC current from the sensor supply for all of the inputs and expansion
relay coils. The I/O requires 456 mA and the CPU provides only 400 mA. This installation
requires an additional source of at least 56 mA at 24 V DC power to operate all the included
24 V DC inputs and outputs.
Table B- 1 Sample power budget
CPU power budget
5 V DC
24 V DC
CPU 1214C AC/DC/Relay
1600 mA
400 mA
Minus
System requirements
5 V DC
24 V DC
CPU 1214C, 14 inputs
-
14 * 4 mA = 56 mA
1 SB 1223 2 x 24 V DC Input/ 2 x 24 V
DC Output
50 mA 2 * 4 mA = 8 mA
1 CM 1241 RS422/485, 5 V power
220 mA
3 SM 1223, 5 V power
3 * 145 mA = 435 mA
-
1 SM 1221, 5 V power
1 * 105 mA = 105 mA
-
3 SM 1223, 8 inputs each
-
3 * 8 * 4 mA = 96 mA
3 SM 1223, 8 relay coils each
-
3 * 8 * 11 mA = 264 mA
1 SM 1221, 8 inputs each
-
8 * 4 mA = 32 mA
Total requirements
810 mA
456 mA
Equals
Current balance
5 V DC
24 V DC
Current balance total
790 mA
(56 mA)