All parameters are specified at 24V, 40A, 3x400Vac, 25°C ambient and after a 5 minutes run-in time, unless noted otherwise.
24
Rockwell Automation Publication 1606-RM005A-EN-P - February 2014
Bulletin 1606 Switched Mode Power Supplies
25.5. Charging Batteries
The power supply can be used to charge lead-acid or maintenance free batteries. (Two 12V batteries in series.)
Instructions for charging batteries:
a)
Set output voltage (measured at no load and at the battery end of the cable) very precisely to the end-of-charge
voltage.
End-of-charge voltage
27.8V
27.5V
27.15V
26.8V
Battery temperature
10°C
20°C
30°C
40°C
b)
Use a 50A or 63A circuit breaker (or blocking diode) between the power supply and the battery.
c)
Ensure that the output current of the power supply is below the allowed charging current of the battery.
d)
Use only matched batteries when putting 12V types in series.
e)
The return current to the power supply (battery discharge current) is typ. 35mA when the power supply is
switched off (except if using a blocking diode).
25.6. Output Circuit Breakers
Standard miniature circuit breakers (MCBs or UL1077 circuit breakers) are commonly used for AC-supply systems and
may also be used on DC branches.
MCBs are designed to protect wires and circuits. If the ampere value and the characteristics of the MCB are adapted to
the wire size that is used, the wiring is considered as thermally safe, whether the MCB opens or not.
To avoid voltage dips and under-voltage situations in adjacent 24V branches which are supplied by the same source, a
fast (magnetic) tripping of the MCB is desired. A quick shutdown within 10ms is necessary corresponding roughly to
the ride-through time of PLCs. This requires power supplies with high current reserves and large output capacitors.
Furthermore, the impedance of the faulty branch must be sufficiently small in order for the current to actually flow.
The best current reserve in the power supply does not help if Ohm’s law does not permit current flow. The following
table has typical test results showing which B- and C-Characteristic MCBs magnetically trip depending on the wire cross
section and wire length.
Fig. 25-9
Test circuit
Maximal wire length
*)
for a fast (magnetic) tripping:
0.75mm² 1.0mm² 1.5mm² 2.5mm²
C-2A
28m 38m 54m 78m
C-3A
26m 35m 50m 74m
C-4A
19m 26m 38m 58m
C-6A
12m 16m 24m 32m
C-8A
9m 12m 17m 25m
C-10A
7m 10m 15m 21m
C-13A
4m 5m
7m
11m
B-6A
19m 26m 35m 59m
B-10A
11m 17m 26m 37m
B-13A
10m 13m 21m 32m
B-16A
8m 11m 14m 24m
MCB
Power Supply
AC
DC
+
-
Load
+
-
B-20A
4m 6m
8m
14m
Wire length
S1... Fault simulation switch
S1
*)
Don’t forget to consider twice the distance to the load (or cable length) when calculating the total wire length (+ and – wire).