Puls QS20.241, QS20.241-C1 Application Note

Q-Series

QS20.241, QS20.241-C1

24V, 20A, SINGLE PHASE INPUT

27. APPLICATION NOTES

27.1. REPETITIVE PULSE LOADING

Typically, a load current is not constant. It varies over time. For pulse load compatibility, following rules must be met: a) The pulse power demand must be below 150% of the nominal power.

b) The duration of the pulse power must be shorter than the allowed Bonus Time. (see output section) c) The average (R.M.S.) output current must be below the specified continuous output current.

If the R.M.S. current is higher, the unit will respond with a thermal shut-down after a while. Use the max. duty cycle curve (Fig. 27-2) to check if the average output current is below the nominal current.

d) For altitudes higher than 2000m reduce the pulse loading (30W/1000m) or the ambient temperature (5°C/1000m)

Fig. 27-1 Repetitive pulse loads, definitions Fig. 27-2 Max. Duty Cycle Curve

utyCycle

PEAK

)

DutyCycle

110 120 130 140

peak

peak + T0

peak -

utyCycle

x T

peak

utyCycle

= 150%

1s - (0.37 x 1s)

0.37

PEAK

=1.7s

PEAK

150%100

)

= 50% curve

1.0

max.

150%

100%

PEAKTPEAK

0.8

0.6

0.4

0.2

Base load (W)

Pulse load (above 100%)

PEAK

Duration between pulses (s)

Pulse duration (s)

PEAK

T0 =

Utilizing the Max. Duty Cycle Curve:

Example to determine the repetition rate of pulses without dipping of the output voltage:

Parameters of application:

Pulse length is T

PEAK = 1s

Steady state load P (= 50% of I

RATED

0=120W

)

Peak load P (= 150% of I

PEAK = 360W

)

RATED

Determining the repetition rate:

1) make a vertical line at P

2) make a horizontal line where the vertical line crosses the P

3) Read the Max. Duty Cycle from the Duty Cycle-axis (= 0.37)

4) Calculate the min. pause (base load) length T

peak -

utyCycle

x T

T0 =

utyCycle

peak

5) Pulse length = 1s, min. pause length = 1.7s

6) Max. repetition rate = pulse length +pause length = 2.7s

More examples for pulse load compatibility:

PEAK

720W 480W 1s >25s 720W 240W 0.1s >0.16s 720W 0W 1s >1.3s 720W 240W 1s >1.6s 600W 240W 1s > 0.75s 720W 240W 3s >4.9s

Jan. 2008 / Rev. 1.3 DS-QS20.241-EN All parameters are specified at 24V, 20A, 230Vac, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.

www.pulspower.com Phone +49 89 9278 0 Germany

19/25

Q-Series

QS20.241, QS20.241-C1

24V, 20A, SINGLE PHASE INPUT

27.2. PEAK CURRENT CAPABILITY

Solenoids, contactors and pneumatic modules often have a steady state 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 Bonus Power®) 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 power supply can deliver extra current. Discharging this capacitor causes a voltage dip on the output. The following two examples show typical voltage dips:

Fig. 27-3 Peak load 40A for 50ms, typ. Fig. 27-4 Peak load 80A for 5ms, typ.

24V

40A

Output Voltage

19.0V

24V

80A 17.5V

Output Voltage

10ms/DIV

Peak load 40A (resistive) for 50ms

Output voltage dips from 24V to 19.0V.

Output Current

Peak load 80A (nearly resistive) for 5ms Output voltage dips from 24V to 17.5V.

1ms/DIV

Output Current

Please note: The DC-OK relay triggers when the voltage dips more than 10% for longer than 1ms.

27.3. BACK-FEEDING LOADS

Loads such as decelerating motors and inductors can feed voltage back to the power supply. This feature is also called return voltage immunity or resistance against Back- E.M.F. (E

lectro Magnetic Force).

This power supply is resistant and does not show malfunctioning when a load feeds back voltage to the power supply. It does not matter, whether the power supply is on or off.

The maximum allowed feed back voltage is 34Vdc. The absorbing energy can be calculated according to the built-in large sized output capacitor which is specified in chapter 8. If the feed back voltage gets higher than 34Vdc, the power supply responds with a shut-down and a subsequent start-up attempt.

27.4. 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) Set the output voltage, at 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

b) Use a 25A circuit breaker (or blocking diode ) between the power supply and the battery. c) Ensure that the output current of the power supply is below the allowed charging current of the battery. d) Use only matched batteries when putting 12V types in series. e) The return current to the power supply is typ. 9mA at 25Vdc when the power supply is switched off.

Jan. 2008 / Rev. 1.3 DS-QS20.241-EN All parameters are specified at 24V, 20A, 230Vac, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.

www.pulspower.com Phone +49 89 9278 0 Germany

20/25

Q-Series

QS20.241, QS20.241-C1

24V, 20A, SINGLE PHASE INPUT

27.5. OUTPUT CIRCUIT BREAKERS

Standard miniature circuit breakers (MCBs) can be used for branch protection. Ensure that the MCB is rated for DC voltage, too. The following tests show which circuit breakers the power supply 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 power supplies. 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 power supply end of the cable (loop impedance approx. 20mOhm)

Fig. 27-5 Branch protectors, test circuit 1

Circuit

Power

Supply

Breaker

Load

Test 2: Short circuit with S1 on the load end (additional impedance included; represents longer load wire length).

Fig. 27-6 Branch protectors, test circuit 2

Circuit

Power

Supply

Breaker

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 8A? The load wire length is 19m.

Answer: A 8A C-Characteristic circuit breaker requires a loop impedance of less than 150mOhm (test results). The wire length table shows that up to 20.9m wire with a cross section of 2.5mm than 2.5mm

shall be used.

82mOhm

120mOhm 150mOhm

Parameters: Input voltage: 230Vac, load current: 0A

Tripping time shorter than 5s. The following circuit breaker tripped during the test:

A- or Z- Characteristic:: equal or smaller 25A *) B- Characteristic: equal or smaller 20A *) C- Characteristic: equal or smaller 13A *)

Parameters: Input voltage: 230Vac, load current: 0A

Tripping time shorter than 5s. The following circuit breaker tripped during the test:

A- or Z- Characteristic:: ≤ 20A and R< 82mOhm *) B- Characteristic: ≤ 13A and R< 120mOhm *) C- Characteristic: ≤ 8A and R< 150mOhm *)

What does this resistance mean in wire length?

0.5mm

0.7mm2 1.0mm2 1.5mm2 2.5mm2 4.0mm2

2.3m 3.2m 4.6m 6.9m 11.4m 18.3m

3.3m 4.7m 6.7m 10.0m 16.7m 26.7m

4.2m 5.9m 8.4m 12.5m 20.9m 33.4m

are below 150mOhm. A wire not smaller

Jan. 2008 / Rev. 1.3 DS-QS20.241-EN All parameters are specified at 24V, 20A, 230Vac, 25°C ambient and after a 5 minutes run-in time unless otherwise noted.

www.pulspower.com Phone +49 89 9278 0 Germany

21/25

+ 4 hidden pages