Rockwell Automation Publication 1606-RM056A-EN-P - December 2016
15
Basic Power Supply 10 A
Application Notes
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 current demanding loads. 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 delivers 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 power converter and 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:
Figure 17 - Peak Load with 2x the Nominal Current for 50 ms, typ
Figure 18 - Peak Load with 5x the Nominal Current for 5 ms, typ
10ms/DIV
Output
Voltage
Output
Current
24V
0A
20A
14.9V
20A Peak load (resistive) for 50ms
Output voltage dips from 24V to 14.9V.
1ms/DIV
Output
Voltage
Output
Current
24V
0A
50A
3.7V
50A Peak load (resistive) for 5ms
Output voltage dips from 24V to 3.7V.
Peak Current Capability
Voltage Dip
Peak Load
Peak current voltage dips
typ
24…14.9V
at 20 A for 50 ms, resistive load
typ
24…7.1V
at 50 A for 2 ms, resistive load
typ
24…3.7V
at 50 A for 5 ms, resistive load