All parameters are specified at 24V, 40A, 3x400Vac, 25°C ambient and after a 5 minutes run-in time, unless noted otherwise.
22
Rockwell Automation Publication 1606-RM005A-EN-P - February 2014
Bulletin 1606 Switched Mode Power Supplies
25.2. 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 BonusPower). 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.
Both the following examples show typical voltage dips:
Fig. 25-3
Peak load with 2x the nominal
current for 50ms, typ.
Fig. 25-4
Peak load with 5x the nominal
current for 5ms, typ.
80A Peak load (resistive) for 50ms
Output voltage dips from 24V to 20V.
200A Peak load (resistive) for 5ms
Output voltage dips from 24V to 12V.
Please note: The DC-OK relay triggers when the voltage dips more than 10% for longer than 1ms.
Peak current voltage dips
typ.
from 24V to 20V at 80A for 50ms, resistive load
typ.
from 24V to 12V at 200A for 2ms, resistive load
typ.
from 24V to 12V at 200A for 5ms, resistive load
25.3. External Input Protection
The unit is tested and approved for branch circuits up to 30A (U.S.A.) and 32A (IEC). An external protection is only
required if the supplying branch has an ampacity greater than this. Check also local codes and local requirements. In
some countries local regulations may apply.
If an external fuse is necessary or utilized, minimum requirements need to be considered to avoid nuisance tripping of
the circuit breaker. A minimum value of 6A B- or C-Characteristic breaker should be chosen.