Rockwell Automation Publication 1606-RM121A-EN-P - October 2020
19
Peak Current Capability
The unit can deliver peak currents (up to several milliseconds) which are
higher than the specified short-term currents. This helps to start loads that
have a high demand for current. Solenoids, contactors, and pneumatic
modules often have a steady-state coil and a pick-up coil. The inrush current
demand of the pick-up coil is several times higher than the steady-state
current and usually exceeds the nominal output current. The same situation
applies when starting a capacitive load.
The peak current capability also helps ensure the safe operation of subsequent
circuit breakers of load circuits. The load branches are often individually
protected with circuit breakers or fuses. If there is a short or an overload in one
branch circuit, the fuse or circuit breaker need a certain amount of overcurrent
to open in a timely manner. This avoids voltage loss in adjacent circuits.
The extra current (peak current) is supplied by the built-in large sized output
capacitors of the power supply. The capacitors get discharged during such an
event, which causes a voltage dip on the output. The following two examples
show typical voltage dips for resistive loads:
Figure 24 - 7.6 A Peak Current for 50 ms, Typ
(2x the nominal current)
Figure 25 - 19 A Peak Current for 5 ms, Typ
(5x the nominal current)
10 ms/DIV
Output
Voltage
Output
Current
24V
0 A
7.6 A
16.5V
1 ms/DIV
Output
Voltage
Output
Current
24V
0 A
19 A
9.5V
Attribute
Values
Notes
Peak current voltage dips
24 V dips to 16.5V typ
At 7.6 A for 50 ms and resistive load
24 V dips to 13.5V typ
At 19 A for 2 ms and resistive load
24 V dips to 9.5V typ
At 19 A for 5 ms and resistive load
