Melcher W Series 125, 250 Watt AC-DC and DC-DC DIN-Rail Converters Convert Select LWN2660-6E-G

The secondary side of the main transformer supplies via the rectifier diode a large electrolytic output storage capacitor providing for the hold-up time. Double-output models exhibit an individual control logic each. The output voltage and the output current are measured and fed back to the primary control logic via an optocoupler. A second control loop monitors the output voltage. It disables the output in the case of a failure in the control logic and limits the output voltage. Built-in temperature sensors monitor the internal temperature of each powertrain. If the temperature exceeds the limit, the converter reduces the output power continuously to keep the temperature below its limit. A green LED on the front cover confirms the presence of the output voltage(s).  

The R input (option R, M1, or M2) allows for external adjustment of the output voltage by means of a resistor or an external voltage source. An external sensor can be connected to the R input and allows for temperature-controlled battery charging (see Accessories). 

Output Power Derating

The output power of LW models must be decreased at low input voltage and/or powertrain temperature above 125 °C.

The powertrain temperature depends on the output power, the input voltage, and the cooling method. At low input voltage the losses increase. At the maximum specified environment temperature TA free air convection cooling might be insufficient approaching maximum ambient conditions. As a result, the output power has to be reduced according to the tables below.

Note: The measurements have been made by the approval boards with free air convection cooling according to 62368-1 3rd edition specified ambient temperature TA and with the converter built in a cardboard box according to UL 508 and a specified temperature outside the box Tout .

The tables give a correlation between TA or Tout and the case temperature TC (measuring point TC see Mechanical Data). For models not specified, please contact the Company

EW models need no derating.

Input Fuse and Protection

A fast-blow fuse (Schurter F 6.3A, 5 × 20 mm), protected by a sleeve, is connected to the input L [W/V]-0.67-1.25-0.67-1.25 or Vi+. EW models have a smaller fuse (250 V, 4 × 9 mm, SOC NT3 6.3A V009, UL-recognized E-39265). For DC input voltages above 250 V consult the Installation Instructions.

Converters with option F have large fuses (F6.3A, 5 × 20 mm). The DC input voltage for converters with option F is limited to 250 V. A VDR and a symmetrical input filter form an effective protection against input transients.

An under- and an overvoltage lockout protect the converter, which is disabled below Vi min and above Vi max by an internally generated inhibit signal.

The built-in bridge rectifier (LW models) provides reverse polarity protection at the input if operated from DC. EW models are protected by the (blowing) input fuse in connection with the body diode of the main transistor. Option Q offers a serial diode, but this reduces the efficiency by approx. 1%.

Parallel Operation

Double-output models exhibit an independent control logic each. Both outputs can be con nected in parallel, provided that options S (included in M1) and R are not used, since they influence only the 2nd output. The two power trains share the current due to their output voltage droop characteristic.

Up to 3 converters with the same output voltage may be operated in parallel. It is possible to parallel W Series with X Series converters.

Reasonable current sharing is achieved by the droop characteristic. Correct mode of operation is highly dependent upon the wiring of the converters and the impedance of these wires. Use wires with equal length and equal cross sections of min. 1.5 mm2. The best results for parallel operation can be achieved with the wiring shown in fig. 6.

Parallel operation of single-output models using the option R (output voltage adjust) is possible, but not recommended.  Refer to f ig. 6; the connections between the pins 8 and 9 (both Vo–) should be as short as possible.

Note: Parallel operation is not possible, if a temperature sensor is connected, as the sensor eliminates the output voltage droop. 

Note: For ORing diodes, we recommend to use Schottky diodes, mounted on a common heatsink to avoid thermal run away (or the use of double diodes).

Output Characteristic and Protection

The output characteristic, individual for each powertrain, is rectangular with a droop to ease parallel operation; see fig. 7. However, a 50% higher output current is possible for a short time, such allowing start-up of loads or charging of capacitors; see fig. 8. Each output is independently protected against internal overvoltage by means of a second control loop. When the output voltage exceeds Vo L , the respective output is disabled.

Overtemperature Protection 1.4 1.6 1.2 1.0 0.8 0.6-- 0.5 0.5 1.5  2.5  s Io / Io nom 05194b 0 1 2 Fig. 8 Short term peak power characteristic: overcurrent versus time (typical values). A built-in temperature sensor protects each powertrain is independently protected against over temperature. When a certain temperature is reached, the concerned powertrain reduces its output power continuously. Thermal Considerations The thermal conditions are influenced by input voltage, output current, airflow, and temperature of surrounding components. TA max is therefore, contrary to TC max , an indicative value only. Caution: The installer must ensure that under all operating conditions TC remains within the limits stated in the table Temperature specifications. Note: Sufficient forced cooling allows TA to be higher than TA max provided that TC max is not exceeded. It is recommended that continuous operation under worst case conditions of the following 3 parameters be avoided: Minimum input voltage, maximum output power, and maximum temperature. Battery Charging and Temperature Sensor The battery charger models exhibit the option M1 and have been designed to charge lead-acid batteries. The R-input allows for connecting a battery-specific temperature sensor, which provides temperature controlled adjust of the trickle charge voltage. This optimizes charging as well as battery life time. Depending upon the cell voltage and the temperature coefficient of the battery, different sensor types are available; see Accessories. Note: Parallel operation is not possible, if the temperature sensor is connected to the paralleled outputs Vo+, as the sensor eliminates the output voltage droop. However, it is possible to insert bleeding resistors in the Vo+ output lines of each converter in order to create a droop of approx. 0.6 V @ Io nom for 24 V outputs (1.2 V @ Io nom for 48V outputs), but this creates considerable power losses.