Rockwell Automation Publication 1606-RM109A-EN-P - August 2020
25
Power Supply —12V, 10 A, 120 W, Single Phase
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 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 for resistive loads:
Figure 30 - 20 A Peak Current for 50 ms , Typical
(2x the Nominal Current)
Figure 32 - 50 A Peak Current for 5 ms , Typical
(5x the Nominal Current)
Figure 31 - 30 A Peak Current for 12 ms , Typical
(3x the Nominal Current)
Peak current voltage dips
Typically from 12-5.9V
At 20 A for 50 ms, resistive load
Typically from 12-6V
At 50 A for 2 ms, resistive load
Typically from 12-5.6V
At 50 A for 5 ms, resistive load
