Refinement of the mains voltage stabilizer LPS-2500RV. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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The voltage in the 220 V mains is not always within the normal range, moreover, emergency situations are not uncommon, leading to significant voltage deviations that are dangerous for various electrical and radio equipment. In such situations, voltage stabilizers can help out. One of them, its capabilities and shortcomings, as well as improvements, will be discussed in this article.

The problem of protecting and ensuring the operability of mains-powered equipment in conditions of a significant deviation of the mains voltage from the norm remains relevant. Due to accidents in the power grid, not only "purely electronic" equipment fails. Electrical appliances, which are considered the most reliable, also break down. Given the fact that today electric irons, washing machines, refrigerators and other household appliances are equipped with electronic "stuffing", it is not surprising that almost all mains-powered equipment has become very sensitive to significant mains voltage drops. In this regard, various commercially available protection devices have appeared on sale. In addition, they are developed and manufactured by radio amateurs, as evidenced by the large number of publications on this topic in the Radio magazine. These devices disconnect equipment from the mains whenever the voltage is out of range. Some turn off the equipment only when the mains voltage rises, others - when it goes beyond the permissible "corridor".

But such devices have a serious drawback. They will not help if the mains voltage "left" the limits of the permissible corridor not for seconds or minutes, but for whole hours. It is not uncommon for cases when the duration of repairing breakdowns in networks is delayed for a whole day or more. But various equipment must work at the same time, and this is not only a refrigerator, but also office equipment, computers. So protection devices will not help out here by disconnecting the equipment from the network. You can't do without a mains voltage stabilizer.

The most affordable and common today are network voltage regulators of the relay type. They are made on an autotransformer and several relays controlled by electronics. Relays switch taps from the winding of a powerful autotransformer, maintaining the voltage at the load within normal limits. Network stabilizers based on voltage converters are much more expensive and less common than relay ones.

The author purchased a relay-type voltage regulator LPS-2500RV (Fig. 1) to power office equipment.

Fig. 1

The entire range of these devices consists of stabilizers LPS-800RV (800 W), LPS-1500RV (1500 W), LPS-2000RV (2 kW), LPS-2500RV (2,5 kW), LPS-4000RV (4 kW), LPS-6000RV (6 kW). They provide switches for operating modes depending on the interval of the mains voltage. The first is 160 ... 250 V, the second - 120 ... 250 V. To power the refrigerator, a delay mode for supplying the output voltage (from 3 to 5 minutes) is specially provided, which is turned on by a special switch, which reduces the likelihood of damage to the compressor motor. In addition to these switches, there are two pointer voltmeters on the front panel. One - to control the input voltage, the second - for the output (stabilized), which is very convenient during operation. To switch the taps of the autotransformer, five identical relays installed on the printed circuit board were used (Fig. 2).

On what has been said, the features of these stabilizers are not exhausted. The maximum load power that can be connected to them depends on its type and is determined by the expression Pmax = Psn / K, where Psn is the power of the voltage stabilizer; K - coefficient determined by the type of load. For example, for a TV and incandescent lamps, K = 1; for an electric drill, K = 1,5; a microwave oven, K = 2; For these consumers, K = 3. In addition, the maximum power must be reduced depending on the value of the mains voltage. At a network voltage of 5 V, the coefficient K \u140d 2, and at 160 V - 1,5. With increasing voltage, the maximum power should also be reduced, but not so much. At 240 V, the coefficient K \u1,1d 260, and at 1,2 V - XNUMX. Thus, taking into account all the nuances, it is better to immediately purchase a stabilizer model with a margin for maximum power. In addition, it is obvious that for consumers such as a refrigerator, it is advisable to have a separate stabilizer.

It should be noted that it is possible to replace the standard autotransformer with a more powerful one. In this case, it is necessary to use an autotransformer on a toroidal magnetic circuit, since there may not be enough space for a W-shaped stabilizer in the housing. But then you will need to replace the relay with more powerful ones. This approach allows you to "purchase" a powerful stabilizer without buying its powerful model at a higher price.

However, the considered stabilizers also have disadvantages. Firstly, the body is made of too thin sheet material. When assembled, it seems quite rigid and durable. But one has only to remove the upper U-shaped cover, as the illusion of structural strength immediately dissipates. It becomes clear why the cover is attached to the body with a large number of screws and self-tapping screws. The presence of a massive autotransformer at the bottom of the case can lead to deformation of the entire lower part of the case. Therefore, when the top cover is removed, one must be careful, because the lower part of the case "comes to life" so much that this structure cannot be moved with one hand.

The second drawback turned out to be more significant, since it is not masked after the case is assembled. At the moment the stabilizer is turned on, a larger starting current (current surge) appears. This leads to the fact that the mains voltage drops sharply and the lighting devices "blink". There is no need to explain that such voltage surges negatively affect the condition of other equipment. In addition, due to the movement of the elements of the magnetic circuit, a blow to the metal case occurs, accompanied by a loud and unpleasant sound. It is obvious that such current surges must be eliminated. One possible option is to use a device that would limit the starting current, the so-called "soft" starter.

A diagram of such a device is shown in Fig. 3.

When connected to the network, the autotransformer of the voltage stabilizer is turned on through the current-limiting resistor R2. At the same time, the mains voltage through the ballast capacitors C1, C2 is supplied to the rectifier, assembled on the diode bridge VD1. Since the winding of relay K2 and capacitor C4 are shunted by resistor R4, the charging of capacitor C3 begins first. After it is charged, the relay K1 will work, its contacts K1.1 will open and the charging of the capacitor C4 will begin. After it is charged, relay K2 will work and its contacts K2.1-K2.3 will close the resistor R2 and the full mains voltage will go to the autotransformer of the voltage stabilizer. This ensures a decrease in the starting current, i.e., stepwise switching on of the voltage stabilizer.

If the mains voltage fails, the capacitor C3 will quickly discharge and its contacts will connect the resistor R4 to the capacitor C4, as a result of which it will quickly discharge and the contacts of the relay K2 will open - the autotransformer will be connected to the network through the resistor R4. Such a construction of the circuit provides a quick return of the K2 relay to its original state, which ensures that the device is ready for a quick reconnection to the network. This is important when the mains voltage fails for a short time. Resistor R4 limits the discharge current of capacitor C4 and protects the contacts of the low-power relay K1 from burning. The zener diode limits the voltage on the relays K1, K2 and capacitors C3, C4, which eliminates the overheating of the relay K1 at an increased mains voltage, because the device is designed to work even at a mains voltage reduced to 120 V. Switch SA1 and fuse FU1 are regular elements of the voltage stabilizer.

A constant resistor PEV-10 (R2) was used, the rest - MLT, S2-23. Oxide capacitors - imported, C1, C2 - K73-17 or K78-2 for an operating voltage of at least 630 V. To improve the reliability of the device, each of the capacitors C1 and C2 can be replaced by two capacitors 1 μFxbZO V connected in series, and in parallel to each capacitor connect a 100 kΩ resistor (MLT-0,5). Relay K1 - RES15 (version RS4.591.001) with a winding resistance of 2200 ohms and an actuation voltage of 18 V. The choice of this type of relay is due both to their presence and to the short release time of its contacts (about 5 ms). Relay K2 - REK28 (KShch4.569.007TU) with a winding resistance of 590 ohms and an actuation voltage of 13 V. One group of contacts of the REK28 relay is designed for a maximum current of 2,5 A, so all three groups are connected in parallel. The zener diode is mounted on a heat sink with an area of ​​15...20 cm2, made of aluminum alloy.

All parts, except for the resistor R2, are installed on a printed circuit board made of fiberglass laminated on one side. Before assembly, it is recommended to check the condition of the contacts of relay K2. As practice has shown, it is desirable to do this, since not only the contacts of used relays, but also new ones, often have increased contact resistance. An experimental test at a current of 1 A of three contacts of the REK28 relay showed that two of them had a contact resistance slightly less than 30 mΩ, and the third - 160 mΩ. After cleaning the surfaces of all contacts, it decreased to 10 ... 20 mOhm, and when they were connected in parallel, the total resistance became less than 5 mOhm. Cleaning contacts has no special features. To do this, you can use a thin soft cloth. It is equally important to be careful not to bend the contacts during cleaning. Their deformation can lead to an increase in transient resistance. If you use only one ballast capacitor C1 (reduce the total capacitance by half), the device will work at a mains voltage no longer of 120 V, but only of 180 V or more. The printed circuit board and the resistor R2 are fixed in the upper part of the rear wall of the voltage stabilizer housing (Fig. 4).

It is known that the parallel connection of relay contact groups does not significantly increase their load capacity. As a result of the spread of the resistance of closed contacts (and it also changes greatly during operation, even if it was initially the same), the current is distributed unevenly between the groups. In addition, the groups of contacts inevitably close and open not simultaneously, which leads to their short-term overloads and increased wear as a result of sparking. We recommend using a relay with a permissible current switched by one pair of contacts as K1, not less than that consumed by the stabilizer at full load and minimum voltage in the network.

Author: A.Zyzyuk, Lutsk, Ukraine

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