Rockwell Automation 1606-XLS240E, -XLS240EA, -XLS240EC, -XLS240E-D Power Supply Reference Manual - Manual (Page 22)

All parameters are specified at 24V, 10A, 230Vac, 25°C ambient and after a 5 minutes run-in time, unless noted otherwise.
22 Rockwell Automation Publication 1606-RM044A-EN-P — March 2014
Bulletin 1606 Switched Mode Power Supplies
23.2. Peak Current Capability
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.
Branch circuits are often protected with circuit breakers or fuses. In case of a short or an overload in the branch circuit,
the fuse needs a certain amount of over-current to trip or to blow. The peak current capability ensures the safe
operation of subsequent circuit breakers.
Assuming the input voltage is turned on before such an event, the built-in large sized output capacitors inside the
power supply can deliver extra current. Discharging this capacitor causes a voltage dip on the output. The following
two examples show typical voltage dips:
Fig. 23-3 Peak load with 2x the nominal
current for 50ms, typ.
Fig. 23-4 Peak load with 5x the nominal
current for 5ms, typ.
10ms/DIV
Output
Voltage
Output
Current
24V
0A
20A 20.5V
Output
Voltage 24V
Output
Current 0A
1ms/DIV
50A 14V
Peak load 20A (resistive) for 50ms
Output voltage dips from 24V to 20.5V. Peak load 50A (resistive) for 5ms
Output voltage dips from 24V to 14V.
Please note: The DC-OK relay triggers when the voltage dips more than 10% for longer than 1ms.
23.3. 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 35Vdc. The absorbing energy can be calculated according to the built-in
large sized output capacitor which is specified in section 6.
23.4. External Input Protection
The unit is tested and approved for branch circuits up to 20A. 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 might 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 4A C-Characteristic breaker should be used.