QTD20.241
Q-Series
24V,
20A,
DC
I
NPUT
21.5.
O
UTPUT
C
IRCUIT
B
REAKERS
Standard miniature circuit breakers (MCB’s or UL1077 circuit breakers) are commonly used for AC-supply systems and
may also be used on DC 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 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 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. 21-5
Test circuit
Maximal wire length
*)
for a fast (magnetic) tripping:
0.75mm² 1.0mm² 1.5mm² 2.5mm²
C-2A
31m 39m 59m 86m
C-3A
24m 31m 43m 68m
C-4A
15m 15m 32m 41m
C-6A
- - - -
B-6A
16m 25m 34m 58m
MCB
Power Supply
AC
DC
+
-
+
-
Load
Wire length
S1... Fault simulation switch
S1
B-10A
- - - -
*)
Don’t forget to consider twice the distance to the load (or cable length) when calculating the total wire length (+ and – wire).
21.6.
S
ERIES
O
PERATION
DC/DC converters of the same type can be connected in series for higher output
voltages. It is possible to connect as many units in series as needed, providing the
sum of the output voltage does not exceed 150Vdc. Voltages with a potential
above 60Vdc are not SELV any more and can be dangerous. Such voltages must
be installed with a protection against touching.
Unit B
-
+
Load
+
-
Input
Output
-
+
Unit A
Input
Output
Avoid return voltage (e.g. from a decelerating motor or battery) which is applied
to the output terminals.
Keep an installation clearance of 15mm (left / right) between two power supplies
and avoid installing the power supplies on top of each other. Do not use power
supplies in series in mounting orientations other than the standard mounting
orientation (input terminals on the bottom of the unit).
Pay attention that leakage current, EMI, inrush current, harmonics will increase when using multiple DC/DC converters.
Oct. 2016 / Rev. 2.0 DS-QTD20.241-EN
All parameters are specified at 24V, 20A, 600Vdc input, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.
www.pulspower.com Phone +49 89 9278 0 Germany
24/27