Datasheet

CPS20.481-D1
C-Series
48V, 10A, DC/DC CONVERTER
22.3. EXTERNAL INPUT PROTECTION
The unit is tested and approved for branch circuits up to 30A (UL) and 32A (IEC). An external protection is only
required if the supplying branch has an ampacity greater than this. Provided, that the negative pole is grounded. If the
positive pole is grounded, an additional external fast-acting input fuse in the negative input is required (E.g. 8A KLKD
fuse from Littelfuse or a comparable UL-Listed fuse with the same ratings and characteristics). Otherwise the status of
the UL approvals becomes void.
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 10A B- or C-Characteristic breaker should be used.
22.4. OUTPUT CIRCUIT BREAKERS
Standard miniature circuit breakers (MCB’s or UL1077 circuit breakers) are commonly used for AC-supply systems and
may also be used on 48V branches.
MCB’s 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 regardless of whether the MCB opens or not.
To avoid voltage dips and under-voltage situations in adjacent 48V 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 PLC's. This requires DC/DC converters 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 DC/DC converter 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. 22-3 Test circuit
Maximal wire length
*)
for a fast (magnetic) tripping:
0.75mm² 1.0mm² 1.5mm² 2.5mm²
C-2A
74m 98m 134m 198m
C-3A
57m 74m 106m 168m
C-4A
43m 56m 73m 114m
C-6A
11m 16m 23m 33m
C-8A
1m 1m 2m 3m
B-6A
19m 36m 51m 82m
B-10A
9m 12m 18m 27m
MCB
Power Supply
AC
DC
+
-
+
-
Load
Wire length
S1... Fault simulation switch
S1
B-13A
7m 10m 16m 24m
*) Don’t forget to consider twice the distance to the load (or cable length) when calculating the total wire length (+ and – wire).
Oct. 2013 / Rev. 1.2 DS-CPS20.481-D1-EN
All parameters are specified at 48V, 10A, 300Vdc, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.
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