CD–Series
DC/DC Converter; 24V, 5A
CD5.242
25. APPLICATION NOTES
25.1. PEAK CURRENT CAPABILITY
Solenoids, contactors and pneumatic modules often have a steady state (sealed) 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
DC/DC converter can deliver extra current. Discharging this capacitor causes a voltage dip on the output. The
following two examples show typical voltage dips:
Fig. 25-1 Peak load 10A for 50ms, typ. Fig. 25-2 Peak load 20A for 5ms, typ.
24V
Output
Voltage
24V
10A
0.7A
10ms/DIV
Peak load 10A (resistive) for 50ms
Output voltage dips from 24V to 17.1V.
17.1V
Output
Current
20A
0.7A
1ms/DIV
Peak load 20A (resistive) for 5ms
Output voltage dips from 24V to 11V.
Output
Voltage
11V
Output
Current
25.2. BACK-FEEDING LOADS
Loads such as decelerating motors and inductors can feed voltage back to the DC/DC converter. This feature is also
called return voltage immunity or resistance against Back- E.M.F. (E
This DC/DC converter is resistant and does not show malfunctioning when a load feeds back voltage to the DC/DC
converter. It does not matter, whether the DC/DC converter is on or off.
The maximum allowed feed back voltage is 30Vdc. The absorbing energy can be calculated according to the built-in
large sized output capacitor which is specified in chapter 7.
lectro Magnetic Force).
25.3. INDUCTIVE AND CAPACITIVE LOADS
The unit is designed to supply any kind of load, including unlimited capacitive and inductive loads.
July 08 / Rev. 1.2 DS-CD5.242-EN / All parameters are specified at 24V, 5A and 48Vdc input at 25°C ambient unless otherwise noted.
www.pulspower.com Phone +49 89 9278 0 Germany
16/21
CD–Series
DC/DC Converter; 24V, 5A
CD5.242
25.4. OUTPUT CIRCUIT BREAKERS
Standard miniature circuit breakers (MCBs or UL1077 circuit breakers) can be used for branch circuit protection.
Ensure that the MCB is also rated for DC voltage. The following tests show which circuit breakers the DC/DC converter
typically trips.
Circuit breakers have huge tolerances in their tripping behavior, therefore, these typical tests can only be used as a
recommendation or for comparing two different DC/DC converters. Furthermore, the loop impedance has a major
influence on whether a breaker trips or not. Two tests were performed, representing typical situations:
Test 1: Short circuit with S1 on the DC/DC converter end of the cable (loop impedance approx. 20mOhm)
Fig. 25-3 Branch protectors, test circuit 1
Circuit
Breaker
I
+
S1
-
+
Load
-
DC/DC
Converter
Input
DC
Test 2: Short circuit with S1 on the load end (additional impedance included; represents longer load wire length).
Fig. 25-4 Branch protectors, test circuit 2
Circuit
DC/DC
Converter
AC
DC
Breaker
I
+
-
R
+
S1 Load
-
*) A list of the circuit breakers under test is available on request.
Example:
Which wire gauge must be used to trip a C-Characteristic circuit breaker with a rating of 3A? The load wire length is
21m.
Answer: A 3A C-Characteristic circuit breaker requires a loop impedance of less than 270mOhm (test results). The wire
length table shows that up to 23m wire with a cross section of 1.5mm
2
1.5mm
shall be used.
180mOhm
270mOhm
Parameters:
Input voltage: 24Vdc, load current: 0A
The following circuit breaker tripped during the test:
A- or Z- Characteristic:: equal or smaller 8A *)
B- Characteristic: no tripping ≥ 6A *)
no breaker available < 6A
C- Characteristic: equal or smaller 3A *)
Parameters:
Input voltage: 24Vdc, load current: 0A
The following circuit breaker tripped during the test:
A- or Z- Characteristic:: ≤ 6A and R= 180mOhm *)
B- Characteristic: no tripping ≥ 6A *)
no breaker available < 6A
C- Characteristic: ≤ 3A and R= 270mOhm *)
What does this resistance mean in wire length?
2
0.5mm
0.7mm2 1.0mm2 1.5mm2 2.5mm2 4.0mm2
5.0m 7.0m 10m 15m 25m 40m
7.5m 10.5m 15m 23m 38m 60m
2
are below 270mOhm. A wire not smaller than
July 08 / Rev. 1.2 DS-CD5.242-EN / All parameters are specified at 24V, 5A and 48Vdc input at 25°C ambient unless otherwise noted.
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CD–Series
25.5. SERIES OPERATION
DC/DC converters can be connected in series to increase the output voltage.
Fig. 25-5 Schematic for series operation
Unit A
Input
Unit B
Input
Output
+
-
+
Output
-
+
Load
-
Earth
(see notes)
Instructions for use in series:
a) It is possible to connect as many units in series as needed,
providing the sum of the output does not exceed 150Vdc.
b) 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.
c) For serial operation use DC/DC converters of the same type.
d) Earthing of the output is required when the sum of the output
voltage is above 60Vdc.
e) Keep an installation clearance of 15mm (left/right) between
two DC/DC converters and avoid installing the DC/DC
converters on top of each other.
Note:
Avoid return voltage (e.g. from a decelerating motor or
battery) which is applied to the output terminals.
CD5.242
DC/DC Converter; 24V, 5A
25.6. PARALLEL USE TO INCREASE OUTPUT POWER
Several DC/DC converter can be paralleled to increase the output power.
Fig. 25-6 Schematic for parallel operation
Unit A
Input
Output
Unit B
Input
Output
Fuse
+
-
Fuse
+
-
*)
+
*)
Load
-
Instructions for parallel use:
a) Use only DC/DC converters from the same series (C-Series) or
consult PULS.
b) Adjust the output voltages of all power supplies to
approximately the same value (±200mV).
c) A fuse (or diode) on the output is only required if more than
three units are connected in parallel.
d) Do not load terminals with more than 25A. Follow wiring
instructions according to chapter 25.7
e) Ensure that the ambient temperature of the power supply does
not exceed 45°C.
25.7. DAISY CHAINING OF OUTPUTS
Daisy chaining (jumping from one power supply output to the next) is allowed as long as the maximum current
through one terminal pin does not exceed 25A. If the current is higher, use a separate distribution terminal block.
Fig. 25-7 Daisy chaining of outputs
max 25A!
Output
+ +
- -
DC/DC
Converter
Output
+ +
- -
DC/DC
Converter
+
Load
-
Fig. 25-8 Using distribution terminals
Output
+ +
- -
DC/DC
Converter
Output
+ +
- -
DC/DC
Converter
+
Load
-
Input
July 08 / Rev. 1.2 DS-CD5.242-EN / All parameters are specified at 24V, 5A and 48Vdc input at 25°C ambient unless otherwise noted.
Input
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Input
Input
Distribution
Terminals
18/21
CD–Series
DC/DC Converter; 24V, 5A
CD5.242
25.8. PARALLEL USE FOR 1+1 REDUNDANCY
DC/DC converters can be paralleled for 1+1 redundancy to gain a higher system availability. Redundant systems
require a certain amount of extra power to support the load in case one DC/DC converter unit fails. The simplest way
is to put two DC/DC converters in parallel. In case one converter fails, the other one is automatically able to support
the load current without any interruption.
Furthermore, redundant systems can be built by using a DC/DC converter powered from a battery and a power supply
with AC input.
- Use the decoupling module YR2.DIODE in combination with two CD5.241-S1 and use the DC-OK signals of the
DC/DC converter to monitor a faulty unit or input voltage.
- Use the redundancy module YRM2.DIODE in combination with two CD5.241 and use the DC-OK signals of the
redundancy module to monitor a faulty unit or input voltage.
Recommendations for building redundant power systems:
a) Use separate input fuses for each DC/DC converter.
b) Monitor the individual voltage sources of a redundant system. A DC-ok lamp and a DC-ok contact is included in
the redundancy module YRM2.DIODE and the DC/DC converter CD5.241-S1. This feature reports a faulty unit.
c) When possible, connect each DC/DC converter to different power sources.
25.9. CHARGING OF BATTERIES
The power supply can be used for float-charging of lead-acid or maintenance free 24V VRLA batteries.
Instructions for charging batteries:
a) Ensure that the ambient temperature of the power supply does not exceed 50°C.
b) Set the output voltage on a disconnected load, very precisely to the end-of-charge voltage according to the
expected battery temperature.
End-of-charge voltage 27.8V 27.5V 27.15V 26.8V
Battery temperature 10°C 20°C 30°C 40°C
c) Use a 6A or 10A circuit breaker (or blocking diode ) between the power supply and the battery.
d) Ensure that the output current of the power supply is below the allowed charging current of the battery.
e) Use only matched batteries when putting 12V types in series.
f) The return current to the power supply is typ. 26.4mA at 25Vdc when the power supply is switched off (except in
case a blocking diode is utilized).
July 08 / Rev. 1.2 DS-CD5.242-EN / All parameters are specified at 24V, 5A and 48Vdc input at 25°C ambient unless otherwise noted.
www.pulspower.com Phone +49 89 9278 0 Germany
19/21
CD–Series
DC/DC Converter; 24V, 5A
CD5.242
25.10. REQUIREMENTS FOR THE SUPPLYING SOURCE
In certain circumstances, the input filter of the DC/DC converter can show a resonant effect which is caused by the
supplying network. Especially when additional external input filters are utilized, a superimposed AC voltage can be
generated on the input terminals of the DC/DC converter which might cause a malfunction of the unit. Therefore,
additional input filters are not recommended. To avoid the resonant effects, the minimal resistance of the supplying
network which depends on the inductance of the input network, shall be above the boundary curve in Fig. 25-9.
Fig. 25-9 Requirements for an input filter
Resistance of the
supplying network
1 Ohm
100 mOhm
stability
10 mOhm
1 mOhm
0.1mH 1mH 10mH
Inductance of the supplying network
)
(
a
)
(
b
(a) max.
(b) typ.
25.11. EXTERNAL INPUT PROTECTION
The unit is tested and approved for branch circuits up to 50A. External protection is only required if the supplying
branch has an ampacity greater than this. In some countries local regulations might apply so check local codes and
local requirements.
If an external fuse is necessary or utilized, a minimum value is required to avoid undesired tripping of the fuse.
B-Characteristic C-Characteristic
Ampacity max.
min.
50A 50A
6A 6A
25.12. USE IN A TIGHTLY SEALED ENCLOSURE
When the DC/DC converter is installed in a tightly sealed enclosure, the temperature inside the enclosure will be
higher than the outside. The inside temperature defines the ambient temperature for the DC/DC converter.
Results from such an installation:
DC/DC converter is placed in the middle of the box, no other heat producing equipment inside the box
Enclosure: Rittal Type IP66 Box PK 9516 100, plastic, 110x180x165mm
Load: 24V, 4A; (=80%) load is placed outside the box
Input: 48Vdc
Temperature inside the box: 42.8°C
(in the middle of the right side of the DC/DC converter with a distance of 2cm)
Temperature outside the box: 24.0°C
Temperature rise: 28.8K
July 08 / Rev. 1.2 DS-CD5.242-EN / All parameters are specified at 24V, 5A and 48Vdc input at 25°C ambient unless otherwise noted.
www.pulspower.com Phone +49 89 9278 0 Germany
20/21
CD–Series
DC/DC Converter; 24V, 5A
CD5.242
25.13. MOUNTING ORIENTATIONS
Mounting orientations other than input terminals on the bottom and output on the top requires a reduction in
continuous output power or a limitation in the maximum allowed ambient temperature. The amount of reduction
influences the lifetime expectancy of the DC/DC converter. Therefore, two different derating curves for continuous
operation can be found below:
Curve A1 Recommended output current.
Curve A2 Max allowed output current (results approx. in half the lifetime expectancy of A1).
Fig. 25-10
Mounting
Orientation A
Standard
Orientation
Fig. 25-11
Mounting
Orientation B
(Upside down)
OUTPUT
DC/DC
Converter
INPUT
INPUT
Converter
DC/DC
OUTPUT
Fig. 25-12
Mounting
Orientation C
(Table-top
mounting)
Fig. 25-13
Mounting
Orientation D
(Horizontal cw)
Converter
INPUT
OUTPUT
DC/DC
Fig. 25-14
Mounting
Orientation E
(Horizontal ccw)
OUTPUT
DC/DC
INPUT
Converter
Output Current
6A
5
4
3
2
1
0
10 20 30
Output Current
6A
5
4
3
2
1
0
10 20 30
Output Current
6A
5
4
3
2
1
0
10 20 30
Output Current
6A
5
4
3
2
1
0
10 20 30
Output Current
6A
5
4
3
2
1
0
10 20 30
Ambient Temperature
40
Ambient Temperature
40
A
2
A
1
Ambient Temperature
40
A
2
A
1
Ambient Temperature
40
Ambient Temperature
40
50
50
50
50
50
A
1
60°C
A
2
A
1
60°C
60°C
60°C
A
2
A
1
60°C
July 08 / Rev. 1.2 DS-CD5.242-EN / All parameters are specified at 24V, 5A and 48Vdc input at 25°C ambient unless otherwise noted.
www.pulspower.com Phone +49 89 9278 0 Germany
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