Decoupling attachments on relays for loads up to 600 volts. Scheme, description

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Decoupling attachments on relays for loads up to 600 volts. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Radio amateur designer

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Electronic devices and components, in the terminal stages of which electromagnetic relays are used, have not lost their relevance among radio amateurs to this day. Despite competition from thyristors and optoelectronic devices, niches remain in load device control circuits where electromagnetic relays are indispensable. Their popularity among radio amateurs is explained by their low cost, versatility (the presence of several groups of contacts), high reliability, and compact instrument cases. Therefore, the use of low-power relays becomes the optimal solution for switching electronic components of medium and high power in high-voltage electrical circuits (with limited dimensions of devices).

To begin with, let's get acquainted with the produced domestic models of low-power relays. They are divided into three types.

1. With one group of changeover contacts:

RES 10 (passports RS4.524.302, RS4.504.314, RS4.504.319), RES 15 (passports RS4.591.003...006, KhP4.591.010... 014), RES 34 (passports RS4.524.372, RS4.524.376) , RES 49 (passports RS4.569.000, RS4.569.423, 424) and others.

2. With two groups of changeover contacts:

RES 6 (passports RF0.452.10Z...104), RES 9 (passports RS4.524.200...201, RS4.524.209, RS4.524.213), RES 37 (passports RF4.510.064, RF4.510.072), RES 47 (passports RF4.500.408, RF4.500.417), RES 48 (passports RS4.590.201, RS4.590.207, RS4.590.213, RS4.590.218), RES 54 (HP4.500.010...011) and others.

3. With four groups of switching contacts: RES 22 (passport RF4.500.131, RF4.500.163, RF4.500.225, RF4.500.231), RES 32 (passport RF4.500.342...343, RF4.500.354...355) and other.

All these electromagnetic relays are designed for a response voltage of 10 ... 20 V. They can also be included in electrical circuits with a slightly higher voltage (up to 30 V) - for this, a limiting resistor of the MLT type with a power of at least 1 W must be connected in series with the relay winding. However, at a voltage of more than 30 V, it is not advisable to use such relays: the total current consumption increases, a large amount of thermal energy is released on the limiting resistor, and at the initial moment of applying voltage to the winding, a power surge can disable the relay.

For all electromagnetic relays used in electrical circuits, the determining parameters are the winding resistance, the operating current and the number of contact groups. These parameters are indicated in the passport for each device.

When designing electronic devices or replacing electromagnetic relays, it should be taken into account that the relay operation voltage (the mathematical product of resistance and current consumption) must be 20 ... 30% less than the voltage supplied to it. This is necessary for reliable switching of the executive contacts of the relay, stable attraction and retention of the armature in conditions of possible vibration of the device.

The electric current flowing through the relay winding must not exceed the limiting collector current of the switching transistor.

When connecting the contacts of low-power relays to 220 V electrical circuits, complications may arise due to overloads during the operation of a particular node, followed by failure of the relay itself. To avoid this, it is necessary to provide a special decoupling prefix in the circuit. The electrical circuits of two such nodes are shown in the figure.

Decoupling attachments on relays for loads up to 600 volts
Schematic diagrams of decoupling attachments for controlling a powerful load up to 600 V DC (a) and an AC load (b)

Figure 1(a) shows a control circuit for a powerful load up to 600 V using a thyristor VS1. Instead of the device indicated on the diagram, you can use KU201, KU202 with letter indices K - N. The diode bridge is replaced by KTs402A, KTs405 with a permissible reverse voltage of at least 150 V. Resistor R1, type MLT, limits the current in the thyristor control electrode circuit. This load device circuit provides a DC supply, rectified by the diode bridge VD1 - VD4. If the load power does not exceed 100 W and the duration of its connection is not long (no more than 1 hour), the thyristor can not be installed on the radiator. Heating of the VS1 case is acceptable within 40 - 60 degrees Celsius. In other cases, the thyristor VS1 should be installed on a cooling radiator or a heat-removing aluminum plate with an area of 36 - 50 cm2. The heat sink must be isolated from the device case. When operating this node, it is necessary to take into account the constant type of current acting on the load. So, for example, connecting an electric lamp to a voltage of 220 V as a load will be justified, but a transformerless power supply with voltage-quenching capacitors will not.

For AC load devices, the electronic assembly is fully suitable, the diagram of which is shown in Figure 1 (b). The triac KU208G is used here as a control element (can be replaced with KU208V). Thanks to the use of a triac (or its analogue - a pair of back-to-back thyristors), there is no need for a rectifier. The KU208 case is identical to the KU201 thyristor case. Installing it on a radiator is determined by the same conditions as in the previous scheme. Thanks to the use of these devices, the contacts of low-power relays of the RES10, RES15 types, which are sensitive to voltage surges in a powerful switched load, are safe, since the current flowing through the K1.1 contacts will not exceed 20 - 30 mA.

When operating components and devices that are under the influence of a life-threatening voltage of 220 V, care must be taken and safety measures - do not touch the elements of the device connected to the network, perform all installation work only when the power supply is turned off.

Author: A.Kashkarov

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