Rockwell Automation 1606-XLE480EPC Power Supply Reference Manual - Manual (Page 19)

Rockwell Automation Publication 1606-RM001B-EN-P - August 2013 19
Bulletin 1606 Switched Mode Power Supplies
23.
Application Notes
23.1 Peak Current Capability
The power supply 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 (including the
PowerBoost). The same situation applies when starting a capacitive load.
The peak current capability also ensures the safe operation of subsequent circuit breakers of load circuits. The load branches are often individually
protected with circuit breakers or fuses. In case of a short or an overload in one branch circuit, the fuse or circuit breaker need a certain amount of over-
current 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:
Fig. 23-1: - Peak load with 2x the nominal current for 50ms, typ.
Fig.23-2: - Peak load with 5x the nominal current for 5ms, typ.
40A Peak load (resistive) for 50ms
Output voltage dips from 24V to 16V. 100A Peak load (resistive) for 5ms
Output voltage dips from 24V to 18V.
Fig.23-3: - 90A Peak load, typ.
Please note: The DC-OK relay triggers when the voltage dips more than 10% for longer
than 1ms.
High Overload Current (typ. >90A for 15ms) enables easy fuse
tripping
Peak current voltage dips typ. from 24V to 16V at 40A for 50ms, resistive load
typ. from 24V to 18.5V at 100A for 2ms, resistive load
typ. from 24V to 18V at 100A for 5ms, resistive load
10ms/DIV
Output
Voltage
Output
Current
24V
0A
40A
16V
15ms
1ms/DIV
Output
Voltage
Output
Current
24V
0A
100A
18V
10ms/DIV
Output Voltage
Output Current
24V
0A
90A peak
18V
15ms