Datasheet

CPS20.241-D1
C-Series
24V, 20A, DC/DC CONVERTER
22.2. INDUCTIVE AND CAPACITIVE LOADS
The unit is designed to supply any kind of loads, including capacitive and inductive loads. If extreme large capacitors,
such as EDLCs (electric double layer capacitors or “UltraCaps”) with a capacitance > 0.5F are connected to the output,
the unit might charge the capacitor in the Hiccup
PLUS
-mode (see chapter 6).
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 24V 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 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 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. 22-4 Test circuit
Maximal wire length
*)
for a fast (magnetic) tripping:
0.75mm² 1.0mm² 1.5mm² 2.5mm²
C-2A
29m 40m 56m 82m
C-3A
26m 35m 50m 77m
C-4A
21m 28m 36m 53m
C-6A
8m 10m 14m 25m
C-8A
4m 7m 11m 18m
C-10A
1m 2m 3m 6m
B-6A
17m 24m 35m 53m
B-10A
12m 16m 23m 32m
B-13A
9m 13m 20m 29m
B-16A
4m 7m 9m 17m
MCB
Power Supply
AC
DC
+
-
+
-
Load
Wire length
S1... Fault simulation switch
S1
B-20A
1m 1m 2m 2m
*) 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-CPS20.241-D1-EN
All parameters are specified at 24V, 20A, 300Vdc, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.
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