All parameters are specified at 48V, 10A, 230Vac, 25°C ambient and after a 5 minutes run-in time, unless noted otherwise.
Rockwell Automation Publication 1606-RM043A-EN-P — March 2014
19
Bulletin 1606 Switched Mode Power Supplies
22. Application Notes
22.1. 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 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. 22-1
Peak load with 2x the nominal
current for 50ms, typ.
Fig. 22-2
Peak load with 5x the nominal
current for 5ms, typ.
10ms/DIV
Output
Voltage
Output
Current
48V
0A
20A
32V
1ms/DIV
Output
Voltage
Output
Current
48V
0A
50A
37V
Peak load 20A (resistive) for 50ms
Output voltage dips from 48V to 32V.
Peak load 50A (resistive) for 5ms
Output voltage dips from 48V to 37V.
Please note: The DC-OK relay triggers when the voltage dips more than 10% for longer than 1ms.
Peak current voltage dips
typ.
from 48V to 32V
at 20A for 50ms, resistive load
typ.
from 48V to 39V
at 50A for 2ms, resistive load
typ.
from 48V to 37V
at 50A for 5ms, resistive load
22.2. Back-feeding Loads
Loads such as decelerating motors and inductors can feed voltage back to the power supply. This feature is also called
return voltage immunity or resistance against Back- E.M.F. (Electro Magnetic Force).
This power supply is resistant and does not show malfunctioning when a load feeds back voltage to the power supply.
It does not matter whether the power supply is on or off.
The maximum allowed feed-back-voltage is 63Vdc. The absorbing energy can be calculated according to the built-in
large sized output capacitor which is specified in section 6.
Summary of Contents for 1606-XLC
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