Puls CD5.242 Application Note

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 [phone] 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.

www.pulspower.com Phone [phone] Germany

17/21