Application features of the ICL series inrush current limiter from MEAN WELL


One of the factors that should be taken into account when creating a power supply system for any load is the presence of an inrush current, its maximum value and duration. Inrush current, input pulse current, or switching pulse is the maximum instantaneous input current consumed by an electrical device when it is first turned on. AC electric motors and transformers can consume several times more than the normal full load current when the power is first turned on for several cycles of input voltage. Power converters also often have inrush currents much higher than their rated currents, due to the charge current of the input filter capacitance.

The choice of overcurrent protection devices, such as fuses and circuit breakers, becomes more complicated when it is necessary to allow high inrush currents. The overcurrent protection should react quickly to overload or short circuit, but should not interrupt the circuit when the (usually harmless) inrush current flows. Therefore, for a number of applications, it is advisable to use inrush current limiters. However, when choosing a limiter, it is important to understand its device and purpose for use so that it performs its function and is as effective as possible. Depending on the type of load – capacitive or inductive – the choice of the inrush current limiter is also determined.

As part of the ICL series inrush current limiter (in the housing and on the DIN rail) of MEAN WELL, an additional resistor is used, which is connected in series to the load supply circuit and limits the flowing current for a certain period of time. The use of an inrush current limiter of this type is advisable only for a capacitive load, since in this way only the charging time of the input capacitance increases and there is no effect on the operation of the other nodes.

Блок-схема ограничителя пускового тока ICLBlock diagram of the ICL inrush current limiter

The resistor is switched on for a limited period of time, during which the starting load current (the charge current of the input filter of the subsequent AC/DC converter) will decrease to a value at which the automatic switch ("automatic") will not be triggered. How to determine the permissible load for the limiter itself, that is, the number of power supplies that can be connected to it, is described here.

The time interval during which the current-limiting resistor in the inrush current limiter is switched on is normalized and specified in the Specification as the INTERNAL RELAY LIMITING TIME parameter. At the end of this time interval, the resistor is shunted by the relay contacts, the additional current drop stops and it will flow completely into the load, without restrictions:

Продолжительность включения реле в ICL-28The duration of switching on the relay in ICL-28

For an inductive load (electric motors, pumps and pumps based on them), the use of an inrush current limiter of this type will be completely useless, since limiting the current in this way will not allow the electric motor to enter operating mode and unwind at full power. For this type of load, a special device must be used – a soft starter device that limits the supply of input voltage for a period of time α, and only the remaining part of the half-cycle of the sinusoidal input voltage is supplied to the load (for example, single-phase power supply):

Принцип ограничения подачи напряжения в устройстве плавного пуска электродвигателейThe principle of limiting the supply of voltage in the soft-start device of electric motors

Current consumption will be proportional to this time interval. In each half-cycle, the cut-off interval α is reduced, the current supply increases accordingly, while the engine, gradually increasing speed, reduces its consumption to the nominal value. Therefore, the key feature of using a soft starter device is not even limiting the starting current as such, but increasing the energy efficiency of the entire installation with an electric motor, improving the quality of the electric motor and increasing its service life.

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