Surge filter: what it is intended for and how it works

Why do you need a surge protector: a brief explanation

The very name of this electronic circuit explains its purpose. The word “filter” indicates the elimination of harmful interference, and “network” identifies its source.

In other words, all electrical debris coming from the power supply is screened out at the input of our device and does not affect the quality of operation of the household appliance. The main network signal of 220 volts with a frequency of 50 hertz passes through the filter without hindrance.

Electromagnetic interference in the network appears spontaneously; it is impossible to predict its occurrence. Even simply turning on an incandescent lamp generates an initial surge of current, creating a zone of transient processes.

Connecting the electric motors of a refrigerator, washing machine or dishwasher is associated with a change in inductive reactance. The current of such switching on can exceed tens or more times the rated load value.

This creates a significant voltage drop in the network. And then there follows a surge, forming high-voltage interference.

These processes take place for a short time. At the time of using analog household appliances, they did not cause much harm, and simple filters were built into audio and video equipment that performed their functions perfectly.

They reliably smoothed out all those quick dips and spikes in voltage by their design, preventing them from reaching sensitive electronic circuitry.

It is important to understand that the filter works exclusively with short-term dips and peaks in the input signal. If such a process takes a little longer, then another device is needed - a voltage stabilizer.. What harm does electromagnetic interference cause?

What harm does electromagnetic interference cause?

1. The voltage of short-term pulses is superimposed on the main power signal of the network 220. In this case, an overvoltage may occur at the amplitude point, which can burn through the working insulation layer or damage the electronic component.
2. Extraneous signals penetrating into low-current circuits distort the operation of sound recording or sound reproducing devices, video equipment, television receivers, and expensive digital equipment.
3. Special equipment allows you to gain access to confidential information through electromagnetic noise transmitted along a neutral conductor laid outside the apartment.

To reliably deal with interference, you need to know the features of your home network.

https://youtu.be/https://www.youtube.com/watch?v=HoumqP1g0eY
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Basic performance characteristics of filters that are important to know

The fight against electromagnetic interference from the network is carried out in different ways. Screen adaptation and the use of electronic components are popular.

Which case combats interference more effectively?

A distinctive feature of high-quality products is a closed metal screen, which eliminates the passage and interference of extraneous electromagnetic signals. It is connected to the ground loop.

In Soviet times, it indicated the diagram of internal connections and technical characteristics of the product.

Such a housing can be made common to the entire device, as is done for a microwave oven or a computer system unit.

Numerous modern modules produced to filter interference from household networks have a conventional plastic casing.

They are deprived of the ability to protect against external interference and extraneous radiation.

In addition, marketers often call ordinary extension cords a surge protector, which is not entirely correct. In this case, their external similarity is used.

How to choose and buy a filter

All of the information listed above should help you decide on the type of device directly in the store.

However, pay attention to two more questions:

1. total power consumption of the connected load;
2. the presence of sockets in the housing that do not provide voltage filtering, but work as a simple extension cord (such a device is also found).

For the device shown in the photo, the maximum permissible load is marked on the back of the case and is limited to 10 amperes.
For normal operation, we recommend having a reserve of about 30 percent minimum, that is, loading this model with no more than 7 amperes. This is quite enough for complex household appliances with electronics. After all, there is no need to power electric boilers, heaters, incandescent lamps and electric motors through a surge protector. They operate normally on voltage with high frequency noise.

We also recommend watching the CompsMaster owner’s video “Choosing a surge protector.”

Now it’s convenient for you to ask questions on the topic and share this material with friends on social networks.

Useful products

• Disappearing ink pen
• Sleeping bag
• Electric shaft with remote control for roller blinds

Basic parameters of network filters

Cross-section of supply wires. Most often, a surge filter (Fig. 6) is produced with a core cross-section of about 0.75 or 1 mm2. This cross-section is considered sufficient since the maximum load current for which the filter is designed usually does not exceed 10 A.

A fuse is also installed for this current. If necessary, you can find a surge filter of increased power, the cross-section of the wires of which reaches 1.5 mm2. The fuse for such a device has a rated current of 16 A.

Rice. 6. Typical surge protector socket.

Length of the network supply wire. The standardized length of the filter power cord is 180 cm. For some models it can be 190 cm, 300, or even 500 cm. Number of sockets. Usually there are 4...6 of them (Fig. 7).

As a rule, all sockets have grounding “ears” (Euro type). There are filters with sockets of different types (1 - universal and 4, 5 - “euro”, Fig. 8).

Rice. 7. Set of sockets.

Number and types of fuses. Fuses are included in the network filter to protect against burnout of varistors in the event of large impulse noise and to disconnect consumers in the event of a short circuit or prolonged overload of the load circuits.

For greater reliability, some manufacturers, in addition to thermal fuses, also install self-recovering fast-acting fuses (based on metal-organic semiconductors).

TOP 7 best network filters

Undoubtedly, a surge protector is an indispensable thing in our time of technological progress. It extends the life of devices and makes people's lives more comfortable. We have compiled a rating of the TOP 7 best models, including:

• HAMA 137254;
• InterStep SP-106K;
• ERA SF-6es-4m-B;
• Power Cube Garant SISN-BLACK-10;
• Uniel S-GSP3-3C;
• APC PM5B-RS;
• Pilot T.

Let's consider each model separately, taking into account its features, advantages and disadvantages, as well as reviews from real customers.

HAMA 137254

The filter is made of heat-resistant plastic and has an elongated black body. There is a general switch for all sockets with a built-in power indicator.

The price is about 999 rubles.

pros

• protective curtains will protect against the ingress of foreign particles and protect children from injury if they act rashly with the socket;
• automatic fuse that cuts off power in case of overload or short circuit.

Minuses

• no USB ports;
• There are no fasteners or holes to position the item vertically.

HAMA 137254

InterStep SP-106K

With this surge protector, you can simultaneously connect six devices and charge two devices. The sockets comply with the Schuko standard and are equipped with grounding contacts. Product color is grey.

Around 990 rubles.

pros

• fire protection building;
• auto overload protection;
• long warranty.

Minuses

Can't be placed vertically.

InterStep SP-106K

ERA SF-6es-4m-B

The model is equipped with short circuit protection. The sockets are recessed into the fireproof housing. Complies with European standards. The surge protector can withstand loads up to 10 A.

Costs about 890 rubles.

pros

• a long cord removes restrictions on the location of electrical appliances;
• The surge protector can be placed in both horizontal and vertical positions due to the presence of wall mounting.

Minuses

no USB.

ERA SF-6es-4m-B

Power Cube Garant SISN-BLACK-10

The surge protector is equipped with a sophisticated indication system that allows you to detect operating faults. There is a special socket with the ability to connect non-standard devices. The length of the cable ensures the comfort of using the device.

Price approximately 1599 rub.

pros

• presence of mounting holes;
• double pole switch ensures safety;
• mechanical protection against foreign objects on each socket;
• indicators of failure, switching on and connection to an outlet with a grounding defect.

Minuses

There are no ports that charge telephone equipment.

Power Cube Garant SISN-BLACK-10

Uniel S-GSP3-3C

The model is designed to connect three devices with a total power of up to 3500 W. It has all the necessary properties, which allows you to effectively protect equipment. Made in white.

For such a product you will pay about 660 rubles.

pros

• compact;
• presence of a pulse noise filter;
• ground contact.

Minuses

does not attach to the wall.

Uniel S-GSP3-3C

APC PM5B-RS

Such a surge protector will protect electronics from surges and help place devices in your home or office in a more convenient way. In case of short circuits and overloads, the device will automatically turn off.

Price approximately 1990 rubles.

pros

• the large distance between the sockets will allow you to connect large network adapters;
• backlit indicators determine the presence of power and contact with the ground line;
• protective curtains.

Minuses

no ports for USB.

APC PM5B-RS

Pilot T

Surge filter made in Russia. The intended design is original in execution - sockets are located on both sides of the switch, and ports for charging devices are located separately.

The device is sold for 590 rubles.

pros

• convenient splitter;
• unusual location of sockets;
• thermal overload protection;
• possibility of fixing on the wall;

Minuses

without wire.

Pilot T

Kinds

The variety of network filters today is great, choosing the necessary model is not difficult. The filter can be vertical or round; it can be used as a tabletop option or hung on the wall; if desired, you can use the surge protector as a built-in one in the countertop. Advanced types of electrostatic precipitators have remote control adjustment. The difference in types of network filters makes it possible to:

• USB port protection - a device with an appropriate connector, for example, a smartphone, media player, etc., can be connected to this design to recharge;
• the ability to turn on each socket separately - conventional models use a single button to turn off the power to the entire surge protector, but there are improved options where the socket can be selected for use and turned on autonomously;
• fastening the surge protector structure to the wall - this can be done using a special loop on the device body, or a strong fastening can be made using 2 fasteners located on the back side of the structure.

How to choose?

The best option, which combines the properties of a surge protector and a stabilizer in one device, is a UPS with a battery, which is an uninterruptible power supply. The UPS is characterized by a smooth sinusoidal voltage drop, so it is used to stabilize the operation of household appliances and computers. The choice of a surge protector for home or professional use is made after studying all the features and characteristics of the electrical network. Many modern buildings have grounding, but there are old buildings that do not have such protection; for such cases, a reliable surge protector is required. Often in one apartment different filters are used for the TV, for the refrigerator, for home equipment.

When choosing a surge protector, you need the following.

• Determine the power of the device - calculate how many devices and with what power will be simultaneously connected to the filter, add a margin of at least 20% to the total number.
• The parameter of the maximum energy of the input pulse is important - the higher this indicator, the more reliable the network device will be.
• Determine whether there is a thermal fuse in the filter that protects the filter from overheating.
• Determine the number of sockets to connect, and if devices need to be frequently disconnected from the network, then it is better to choose a filter with autonomous shutdown of each socket.
• Consider what length of electrical cable will be needed.

Design

Therefore, the windings of each inductor must be identical and symmetrically wound on magnetic cores. Additionally, it is advisable to place a ferrite washer on the power cord near the extension cord, most conveniently a split washer with latches - fig.

No matter how it looks, no matter what case the manufacturer puts it in, no matter what other ergonomic features they come up with, the main thing is that all this external elegance does not overshadow the main tasks.

How can this situation be prevented? The power cord 7 is connected to the surge protector.

With all this, the price indicator, which supposedly, the more expensive, the better and better quality, does not matter in this situation. The suitable wires should be kept as short as possible. A high-pass filter transmits the high-frequency signal unchanged, but attenuates the low-frequency signals.

Online store

Its windings contain 25 turns and are wound with the same wire and in the same way as the windings of inductor L1. Some of them are filters ready for installation on a printed circuit board.

From this graph it is clear that the higher the frequency of interference, the more effectively it is suppressed. No matter how it looks, no matter what case the manufacturer puts it in, no matter what other ergonomic features they come up with, the main thing is that all this external elegance does not overshadow the main tasks. The second scheme is more efficient, hence the corresponding name of the surge protector by the manufacturer - Pilot Pro, the maximum current of which is also 10 amperes; but essentially also primitive. There is a whole class of network filters in which the grounding wire has no connection with the internal circuit, except for the corresponding contacts of the Euro sockets themselves and the grounding contact of the Euro plug. In addition to such options, there are also models where the power cord passes through a ferrite ring, or makes a couple of turns around it.

Homemade surge protectors Often, cheap filters available for sale are not actually filters. Tweets by qrzru Scheme of a simple surge protector for household appliances Surge protectors have become an integral mandatory accessory for office equipment and some household appliances and appliances. Resistors connected in parallel to the capacitors R The loop at the end needs to be cut, ideally - immediately wound with two parallel wires. And if you consider that many people have several unnecessary, inoperative devices, it turns out that spare parts are literally lying around under our feet.

The power cord 7 is connected to the surge protector. Uniel S GSP4 surge protector Operating principle of the surge protector The mains supply is alternating current voltage, which varies according to a sinusoidal law. This part consists of a ferrite core and lacquered copper wire wound around it. How to properly connect an RCD? Connection diagrams.

How to make a filter at home

Making a surge protector with a switch with your own hands is not very difficult; in terms of efficiency, this device will not be inferior to Sven Optima Base 5 m Black, Power Cube, Belkin (Belkin), APC PF8VNT3-RS.

Let's look at the step-by-step instructions:

The extension cord consists of two fuses, one acts as a switch (different ones are connected in the photo). And the other - a circuit breaker, a varistor, contact connections. The varistor is the main protection of all stabilizers. Separately, it should be noted that most schemes are based on the principle of connecting a simple extension cord and a filter; (the number 14 doesn’t mean anything, most likely it’s just a batch number)

C2 is a capacitor; it must have long wires, because otherwise, you will not be able to install the contact plates. But keep in mind that cords that are too long will reduce the effectiveness of the extension cord; If you install homemade network filters for a refrigerator, audio equipment (cassette recorders, home theaters), televisions and other office equipment, then you need to mount a ferrite washer near the network cable; it will prevent interference; Next you need to select varistors. It is believed that the optimal size is 471 with a diameter of 6 to 10 millimeters; Next come the electrical resistors in the circuit R1, R2. To prevent household appliances from transmitting interference, you need to select powerful resistors with the maximum allowable resistance. To calculate this data, you need to calculate the ratio of the power consumed by all devices included in the filter. For laptops, the average resistor should be 5 ohms; for more powerful devices, two-watt resistors are used; Now we mount the chokes, in the drawing L1, L2. The main requirements put forward are: a ferrite core (pulse filters without it have poor inductance), an open-class armature or an air gap

It is very important that the inductor has the highest current equal to the coil current; The DC consumer must be equipped with capacitors (C1, C2); depending on the size of the unit, one or both capacitors can be installed. And the last thing to install is resistor R3. We select it depending on the required kW or W

It should be noted that these units are seriously loaded by the power supply system, so they must be quite large and powerful; If necessary, install the device on a stand. When finished, perform a throughput test.

Various amateur radio circuits for assembling a surge protector for equipment:

Photo - Initial extension cord circuit Photo - Surge filter

Photo - Surge filter circuit

Using this information, you can make a linear machine with your own hands. In this case, power supplies can have any power and frequency readings; the main thing is to calculate the throughput of individual parts.

Ways to Improve the Filter Circuit

There are many options for improving the network filter circuit. One of them is ingenious and allows you to significantly save energy consumption. The essence of the method is as follows:

1. Open the housing of the multi-connector SF extension cord.
2. One of the current-carrying busbars is cut.
3. The segments are connected to a 5 volt relay, designed for switching current 3A, 250 V.
4. The other two relay contacts are connected by wires to a USB connector at the end.
5. The connector is connected to the USB input of the TV.

The result is a controlled power system consisting of a TV, a digital set-top box and a satellite dish power supply. If previously, when the TV was turned off, all parts of the system remained in standby mode, then with the upgraded filter they are completely turned off. As soon as you turn on the TV using the remote control, all the switched devices are also activated and vice versa.

In another case, they take the path of adding an LC filter to the SF, which, in addition to suppressing interference from the network, reduces mutually occurring electrical interference from connected consumers.

A standard varistor (470 V) often does not trip the automatic fuse. It is replaced with a similar device designed for a voltage of 620 V. This allows you to suppress interference from a running washing machine, vacuum cleaner and other powerful electrical equipment.

Home craftsmen equip surge protectors with audible alarms. When the voltage level in the network exceeds 280 V, the filter notifies you with a signal.

Industrial and homemade filters for a three-wire power system

Among the mass-produced products there are quite useful technical solutions that the home craftsman should pay attention to

Brief overview of useful functions of factory models

One of the popular developments, widely represented in the trade, is the Pilot series of filters of different designs.

The circuit diagram of the Pilot surge protector is shown in the picture to make it easier to understand its capabilities.

I will dwell on the tasks that Pilot XPro, specially created for comfortable work, extending the life of connected consumers and reducing electricity consumption, is designed to solve. This:

• protection against surge voltages by varistors;
• prevention of high-frequency interference by inductive-capacitive reactances;
• power management through the introduction of the Master Control function;
• protection against overvoltage associated with zero loss;
• smooth switching off and switching on of equipment under load with the Zero Start function due to the elimination of current surges by the built-in circuit;
• automatic switching on of consumers after elimination of emergency power failure;
• two levels of protection against current overloads or short circuits due to a fuse and a bimetallic release;
• indication of network connection and supply voltage level;
• temperature control and automatic shutdown when overheating.

The Master Control function defines one socket as the main socket (as a master socket). The main consumer with a power of more than 50 watts is connected to it, for example, a computer system unit.

When it is turned on, the automation simultaneously powers three other sockets with peripheral equipment. It also turns them off when power is removed from the main unit.

There are sockets on the case that are not controlled by microprocessor automation. They are used for lighting, telephones, and other equipment.

You can find out more detailed information about this equipment in a short video by the owner of ZIS Company.

Filters

Designed to suppress interference. There are purely capacitive and inductive-capacitive ones based on LC circuits. Surge filter coils are available without cores or with ferrite cores (best on ferrite rings).

Additional devices. Indicators for switching on and the operational status of the protection on LEDs or neon bulbs glow when the filter (or its separate channel) is on and go out when the fuses trip. Arresters (gas) protect varistors at large amplitudes of impulse noise.

Any electrical appliance requires proper operation. There are also a number of safety rules regarding network filters. It is contraindicated to connect filters to each other.

Rice. 8. Example of a filter with Euro sockets.

This may unnecessarily increase the current in the ground wire. In addition, devices with high inrush currents (vacuum cleaners, air conditioners, refrigerators, etc.) cannot be connected to surge protectors. It is not recommended to connect surge protectors to uninterruptible power supplies as this may damage the protection circuits.

Making your own surge protector

It will not be at all difficult for a radio amateur to make the simplest surge protector with his own hands at home. To do this, you need to build a small circuit inside the body of a power strip with several outlets. The picture below shows how to do this.

DIY SF

Install the SF in the extension cord as follows:

1. Open the housing of the power strip.
2. Resistors R1, R2 and chokes (inductive coils) L1, L2 are soldered into parallel branches after the switch and varistor.
3. Then the branches are alternately closed through capacitor C1 and one resistor R3.
4. Installation of the end capacitor C2 can be done anywhere between the sockets.

Important! If there is no room inside the extension cord housing for the second capacitor C2, then you can do without it. It is enough to adjust the parameters C1

Chokes are used with open ferrite cores with inductance from 10 μH. Capacitors are selected in the range of 0.22-1 µF. The resistance of the resistors correlates with the planned power of consumers. At a load of 500 W, 0.22 Ohm resistors will be required. Resistance R3 must be at least 500 kOhm.

Repair - what to do if the surge protector button is broken

If, when you turn on the surge protector button, extraneous sounds begin to be heard, which are accompanied by the smell of melting plastic, the device should be immediately de-energized. Next, you need to disassemble the surge protector and check the condition of the contacts on the switch.

To do this you will need the following tools:

• soldering iron,
• crosshead screwdriver,
• tester,
• sandpaper-zero.

If the contacts are burnt out, the tester readings will confirm this (in this case, there will be no voltage at the output from the button in the “On” position). To clean the contacts, the switch needs:

1. Disassemble the surge protector housing by unscrewing the mounting screws;
2. Unsolder the button and remove it from the filter housing. The button is held in the housing by plastic clips, which should be carefully squeezed out.
3. Disassemble. To do this, you need to disconnect the key by picking it up with a flat-head screwdriver.
4. Take out the contacts and clean off any black deposits.
5. Assemble the button. After this, we assemble the button in the reverse order, install it in place and solder it.

If the contacts have burned very badly and melted the plastic of the switch housing, it should be completely replaced.

To do this you need:

1. Disassemble the filter;
2. Unsolder the button;
3. Remove the switch from the housing;
4. Install a new one in its place (sold in radio parts stores, costs about 30 rubles);
5. Solder the button and assemble the filter housing.

Often the button on the surge protector does not work due to mechanical damage. The most common case is the breakdown of the latches that hold the switch key in the housing. In this case, it is not necessary to buy a new button - the latches can be restored.

To do this you will need the following materials and tools:

• screwdriver (or drill) and drill with a diameter of 3.5 mm;
• toothpick;
• cotton swab;
• side cutters.

The process itself is very simple:

1. A through hole is drilled in the key into which a cotton swab is inserted (it will act as a latch).
2. A toothpick is inserted inside the cotton swab for greater rigidity. On both sides, the improvised retainer is trimmed with side cutters so that on each side it protrudes approximately 3-4 mm.
3. Now all that remains is to insert the key into the body - to do this, just slightly bend the sides of the seat with a screwdriver.

VIDEO INSTRUCTION

Uninterruptible power supply (UPS)

In a specialized store, sellers may vie with each other to offer a stabilizer, a surge protector and a UPS. What is better to buy is difficult to decide right away given the existing large selection of models with different names and properties.

Many people purchase a UPS to eliminate one possible fault in the network - a sudden loss of voltage, in order to correctly shut down the operation of electronic devices. Imported models are designated UPS. It is advisable to purchase them with a stabilizer function to eliminate radio frequency and electromagnetic distortion and interference.

If the supply voltage disappears or decreases beyond the required range, the UPS switches to working through batteries. Depending on the model used, the operating time of an independent source can reach several minutes or hours. The device is selected according to the power of the equipment being protected.

An important characteristic of a UPS when operating on battery power is the output voltage shape. For cheap devices it is rectangular, and in frequency and amplitude it is equal to the mains sinusoidal voltage

Device

If we talk about the design of such a thing as a surge protector, then it should be said that it can belong to one of 2 categories:

• stationary-multichannel;
• built-in

In general, the circuit of a conventional surge protector designed for a voltage of 220 V will be standard and, depending on the type of device, may differ only slightly.

Other equipment also has such boards, which falls into the category of complex ones. Such boards usually consist of the following components:

• additional type capacitors;
• induction coils;
• toroidal type throttle;
• varistor;
• thermal type fuse;
• VHF capacitor.

A varistor is a resistor that has variable resistance. If the standard voltage threshold of 280 volts is exceeded, then its resistance decreases. Moreover, it can decrease by more than ten times. A varistor is essentially a surge protector. And stationary models usually differ in that they have several outlets. Thanks to this, it becomes possible to connect several models of electrical equipment to the electrical network through a surge protector.

In addition, all surge protectors are equipped with LC filters. Such solutions are used for audio equipment

That is, such a filter is noise suppressing, which will be extremely important for audio and working with it. Also, surge protectors are sometimes equipped with thermal fuses, which help prevent voltage surges.

Sometimes some models use disposable fuses.

How the filter works

The mains voltage of 220 volts is variable and has a sinusoidal shape. However, the sinusoid is not presented in its pure form, but with electromagnetic interference. Ideally, a sine wave looks like a wavy line, but in reality the voltage has spikes, phase imbalances, etc.

Network interference affects the performance of sensitive electrical appliances. Therefore, there is a need to filter the current from unnecessary interference. For these purposes, a surge protector is used, which is connected between the electrical network and the consumer. The filter device is made according to a unique scheme of capacitors and chokes. The main function of the filter is to block high-frequency interference and spurious pulses. The former are handled by inductances, and the latter by capacitances.

Stabilizer circuits

In a stabilizer, the voltage is regulated in different ways. One of them is switching the secondary windings of the transformer.

The voltage change is made by electronic keys controlled by the processor. Data comes from the sensor and is switched using an electronic switch on thyristors.

Parametric stabilizers use the phenomenon of avalanche breakdown on zener diodes, when the voltage remains constant despite a significant change in current. To amplify the power, the load is connected through one or more transistors.

Capacitors are used as high-frequency filters in the circuit. A stabilizer is a complex device that may include a surge protector.

The input resistor allows you to keep the transistor open and also maintains the zener diode in the active region.

The stabilizer is selected according to the power of the consumers. Nowadays, electronics are used everywhere, for example, in control units for energy-saving lamps. Therefore, it is needed not only for computers, but also for lighting systems. If it is used for electric motors, you should know that the starting current of the latter is several times higher than the rated current. Despite the fact that stabilizers allow short-term overloads, here a larger power reserve should be taken.

General information. What is needed – selection of diagrams and equipment

PEMINs appearing in the power supply can have a negative impact on the operation of other low-current devices (TVs, digital equipment, radios, etc.) or cause interference in the reception of various signals. In addition, PEMIN can become a source of leakage of all confidential information, for example, during the operation of special equipment (information can be intercepted via grounding or power circuits).

It is the surge protector that helps protect devices, as it will perform two functions at once:

• 
  Cut off high frequency signals in the power circuit.

• Protects devices in the home from high voltage surges.

Most people very often come across power filters that are already built into the electrical type extension cord. But, manufacturers or traders are often misleading. Certain filter models will not actually perform the filter's stated function and will only provide short-term overload protection when the voltage or current increases (short circuit).

As part of network filters, there is only one varistor (this is an element of the electrical circuit that will implement the function of a variable resistor, which increases the resistance when the applied voltage increases) and a self-acting type of switch (a fuse that trips when the current force rises sharply). Such a device can only help, for example, against interference created by a lightning discharge during a thunderstorm. Devices that 100% implement the list of filter capabilities cost much more than their adapted analogues.

Thus, network-type filters can be called products from the Pilot company (the series starts with Pilot L, Pilot GL, etc., with the exception of Pilot S), and prices for them start from 1,000 rubles, or analogues from APC, IPPON, BURO and others . For this reason, there is a completely natural desire to make an inexpensive, but no less active surge protector yourself. First of all, you can convert a purchased inexpensive filter with varistor protection for high-frequency filtering.

To modify it you will need:

• Ferrite filter.
• Resistors.
• Capacitors.
• Varistor (you can leave the existing one in the extension cord if it is there).
• Inductors or chokes.

Next, let's talk about schemes.

Device and circuit

The network filter circuit is quite simple. In order to understand how this device works, it is necessary to understand how to suppress intermittent interference in the network. For example, resistors. The resistance of these devices does not depend on the strength of the current that passes through them. But inductance and capacitance are directly proportional to current. That is, it turns out that the higher the current and voltage, the more the resistance of the inductor increases.

This quality is used in filters to suppress short-term voltage surges with a large magnitude. To do this, you just need to install two inductors in the phase and neutral conductors. By the way, their inductance can be located in a fairly wide range from 60 to 200 μH.

Internal structure of the surge protector

As for resistors, they can also be installed in a surge protector for a computer or TV.

Experts believe that among all the models offered today, LC surge protectors are effective. The thing is that in their design, in addition to inductors, capacitors are also installed. By the way, their capacitance varies from 0.22 to 1.0 µF. It must be taken into account that the capacitor voltage should be almost twice the mains voltage. This is a reserve in case of a high surge.

Why such a complex scheme?

• “L” is a coil that will level out current surges.
• “C” is a capacitor that will absorb high voltage surges.

Let's return to impulse noise. They can be extinguished using a special semiconductor element - a varistor. Essentially, this is a resistor that in normal mode, that is, at low voltage, has a high resistance and does not allow current to pass through itself. As soon as the current in the network rises to the nominal value (470 V) of the variator, it resets the resistance and allows current to pass.

Network filter circuit

So, let's summarize. A surge protector for a computer or other household electronic device must contain in its design:

• Two coils connected in series.
• A capacitor connected in parallel.
• Varistor.
• Resistors.

General arrangement and equipment of shower cabins

The standard set of shower cabins is easy to assemble and includes several basic elements:

1. The lower part, most often presented in the form of a metal frame and pallet.
2. The back panel on which the main functionality of the device is located.
3. Side walls.
4. Entrance door with guides (may be absent or replaced with curtains).
5. The upper part, which may be missing in some models.

In addition to the basic configuration, the shower stall can come with various devices and accessories designed for more comfortable use.

Homemade surge protectors

Often, cheap filters available for sale are not actually filters. For example, an extension filter (Fig. 9). Inside there is only a varistor that limits short-term high-voltage pulses that sometimes occur in the network, and a current switch that is triggered when a large current flows (Fig. 10).

Rice. 9. Extension filter.

Rice. 10. What's inside the extension filter.

There is a button on the housing that must be pressed to close the breaker again if it has tripped. To turn this extension cord into a full-fledged filter, you need to build filter circuits inside.

In the original circuit (Fig. 11a), S1 is a current breaker, VR1 is a varistor of type 471 (the maximum voltage is coded by the number, and the maximum energy of the suppressed pulse depends on the diameter).

Rice. 11. Diagram of filter circuits for installation in an extension socket.

In the modified version (Fig. 11 b), an RLC filter is added. Coils L1 and 12 together with capacitors C1 and C2 form an LC filter.

The inductive reactance of the coils increases at high frequencies. To attenuate low-frequency interference, resistors R1 and R2 are connected in series with the coils. Resistor R3 discharges the capacitors when the filter is disconnected from the network. When assembling the filter (Fig. 12), the standard varistor is left (type 471, with a diameter of 6...10 mm).

The greater the resistance of resistors R1 and R2, the better the filtration, but the greater their heating and voltage loss in the filter. Therefore, the resistance of the resistors is selected depending on the total power consumed by all those devices that will be connected to the filter (at the specified ratings RNag.max = 250 W).

Chokes L1 and L2 are industrial high-frequency, type DM-1 with an inductance of 50...100 μH. Capacitors are film capacitors, type K73-17 or similar (imported ones are smaller in size) with a capacity of at least 0.22 μF (more than 1 μF is also not needed). The resistance of the RE resistor is not critical (from 510 kOhm to 1.5 MOhm).

Additionally, it is advisable to place a ferrite washer on the power cord near the extension cord (the most convenient is a split washer with latches - Fig. 13).

Rice. 12Assembling the filter.

Rice. 13. Ferrite washer.

Another version of the noise suppression network filter circuit is shown in Fig. 14. For greater efficiency, it consists of two links connected in series.

The first (capacitors C1, C4, C5, C8, C9 and two-winding inductor 12) is responsible for suppressing interference with frequencies above 200 kHz.

The second link (two-winding choke AND with the remaining capacitors) suppresses interference, the spectrum of which extends below the specified frequency (down to several kilohertz).

Rice. 14. Scheme of an interference suppression network filter.

Thanks to the magnetic coupling between the windings of the inductors, common-mode interference (those that are simultaneously induced or emitted by both network wires) is suppressed.

Therefore, the windings of each inductor must be identical and symmetrically wound on magnetic cores

It is important to ensure correct phasing of the windings

Their beginnings are indicated by dots in the diagram. Inductor L1 is wound on a ferrite magnetic core Ш12×14 with a homemade frame made of electrical cardboard folded in half with 00.63 mm PELSHO wire. The winding contains 87 turns. The brand of ferrite, unfortunately, is unknown. The inductance of each winding measured by the 1.P235 device is about 20 mH.

For inductor 1.2, armored magnetic wire B22 made of 2000NM1 ferrite was used. Its windings contain 25 turns and are wound with the same wire and in the same way as the windings of inductor L1. The inductance of each inductor winding L2 is 120 μH.

The capacitors of the first filter section are mica. Since there are no small-sized capacitors of this type with the required capacitance for the filter for the required voltage, we had to connect KSO-5 capacitors of smaller capacity in pairs in parallel.

A similar solution, but with a pairwise series connection of capacitors C2, C3 and C6, C7 (film capacitors made abroad), was adopted in the second filter section to ensure the required operating voltage.

Resistors R1...R4 connected in parallel to the capacitors equalize the voltages applied to them and ensure rapid discharge of all capacitors after disconnecting the filter from the network. Capacitor C9 is type K78-2. The filter board is placed in a grounded metal box.

The material was prepared by V. Novikov. RM-07-12, 08-12.

Information sources:

1. electroclub.info
2. corumtrage.ru
3. potrebitel.ru

Homemade power filter

I bring to your attention two very simple but reliable methods on how to make your own power filter for a car radio. The main advantage of the presented homemade devices is their price and ease of manufacture, which in no way relieves you of personal responsibility for the possible consequences of connecting homemade power filters.

Method one

This circuit consists of four capacitors and a coil:

Make your own filter for car radio

• The capacitances of the capacitors are taken at 4700 and 1000 μF (be sure to shunt them by 0.1 μF);
• A coil with an inductance of 100 microhenry has a winding on a ferrite ring made of enamel wire with a cross-section of 0.9.

Filter for car radios

The advantage of this circuit is that each element in it plays the role of a kind of filter: electrolytic capacitors smooth out various interferences and pulsations, and shunt “conductors” eliminate high-frequency interference.

Advice! It is advisable to tin the conductive paths on the “signet” with a thick layer.

Car radio power filter

Second way

The circuit of this simple LC filter also consists of a coil with capacitors, although with the addition of reverse polarity protection (diode) and a fuse.

Filter for car radio power supply

Before assembling the circuit, we need to make a choke, which will also consist of a ferrite ring and a winding wound on it in the form of 10...15 turns of wire with a cross-section of 1...1.5 millimeters (for convenience, you can use three strands of wire with a cross-section of 0 .5 millimeters each).

Advice! Instead of a ferrite ring, you can use a ring made of powdered iron, which is used in computer power supplies (white or yellow ring).

The advantage of this particular circuit is that it works with a very wide range of nominal values ​​of the components included in it. The capacitance of the capacitors is not critical and varies from 1000 to 4700 μF (the more the better), and it is also possible to use electrolytes with voltages from 16 to 100 Volts (higher voltages do not make sense). This concludes the instructions on how to make a filter for a car radio yourself; I hope you will find it useful and will rightfully take its place in your personal collection of useful tips.

Description of the operating principle

A standard surge protector passes electrical current through a cable from the outlet to a number of electrical and electronic devices connected to the device. If the voltage from the outlet rises above the permissible level, the uninterruptible power supply device diverts additional electricity from the outlet to the ground wire.

The most common type of surge protector has a component called a metal oxide varistor, or MOV, that removes the extra voltage. The MOV forms the connection between the phase power line and the ground line.

The varistor itself consists of three parts: an oxide-metal part in the middle of the cable connecting to the power supply and grounding lines, which are made of two semiconductors. These semiconductor devices have variable resistance that varies with voltage. When the voltage is below a certain level, the electrons in the flux semiconductors combine in such a way as to create a very high resistance. If the voltage exceeds this level, the electrons behave differently, creating lower resistance. If the voltage matches the specified resolution, the varistor does nothing.

Photo - Main line filter

As soon as the additional current is diverted to the filter and to ground, the phase line voltage returns to normal levels. Thus, the surge protector Pilot (Pilot), Defender, and others only remove the pulse current, while allowing other devices connected to the conductor to continue operating at a normal rhythm. In other words, network noise suppressors operate like a pressure-sensitive valve that only opens when too much pressure is applied.

Photo – Professional filter circuit

Principle of operation

Based on their functionality, network filters are divided into:

Simple filters

These include varistor products, which include:

Filters with varistors

They can be made from a single semiconductor or an assembly of them.

Single module

One varistor is used in the simplest protections.

At the nominal power supply of the network, it has high electrical resistance and does not allow current to pass through itself. If the voltage increases to a critical value of the order of 470 volts, then the semiconductor junction of the varistor breaks through and eliminates the overvoltage by closing potentials through its internal junction, which is accompanied by the release of thermal energy.

Varistor assembly

The classic circuit is assembled on the basis of a triangle with grounding of the middle point. Filter varistors protect the load from symmetrical and asymmetrical overvoltages in the network.

Grounding increases the efficiency of the circuit and removes interference through an additional wire connected to the ground loop.

Cheap surge protectors with a separate varistor assembly are widely used in everyday life. They do not filter high-frequency voltage interference signals, but can only limit the overvoltage pulse.

Overcurrent protection

High voltage that slips through varistors when they fail or for other reasons creates increased load currents on the connected equipment. To limit them, current protection is installed on the network filter:

The second option is preferable: to put it into operation after the protection has been triggered, just press the corresponding button. This is more convenient than opening the case and changing the fuse, which still needs to be found first.

Electronic LC circuits

The principle of operation of the protection

The electrical resistance of resistive elements does not change depending on the type of current that flows through them. A completely different picture emerges for reactive elements:

Their resistance is directly dependent on the frequency of the signal.

Expert opinion

It-Technology, Electrical power and electronics specialist

Ask questions to the “Specialist for modernization of energy generation systems”

Surge filter and voltage quality of household electrical wiring | Do-it-yourself apartment design and renovation In addition to finished structures, the domestic industry produces modules of two-stage network filters, for example, from the D19 series (Fig. Ask, I'm in touch!

Network interference filter circuit

This filter is a very simple and neat design. In terms of design improvements, it may include a toroidal core inductor, overvoltage protection on thermistors and varistors.

The chokes here are used from an EMI / RFI filter from a switching power supply, naturally, inductors with windings wound on one core will of course be a priority for such a filter, but not everyone has them (and has the desire to wind them correctly), so a simplified option was chosen - there will still be excellent filtration.

The resistor heats up a little, so it is advisable to replace it with a more powerful one, because with a slight increase in the network voltage above 250 V it can already heat up significantly.

It is better to place the fuse behind the socket so that the capacitors do not cause a fire if they short circuit in case of severe overvoltage. If possible, add high energy varistors for surge protection. As for the resistor, it should be a metallized resistor from the high voltage series. Here is an example of an industrial filter:

Using small distances between board traces is also justified, especially when it comes to surge protection. The picture below shows a factory installed surge protection solution, of course this does not replace the spark gap, but how not having any protection at all will provide large losses in the event of a possible problem.

This high-energy spark gap is the so-called lightning protection. Its task is to take over and destroy most of the energy in the event of damage to the varistor. It is assumed that in the event of a high energy discharge, an arc will occur between the electrodes of the spark gap, causing not only the loss of most of the energy, but also sputtering of the copper traces, causing metallization of the gap and, consequently, a short circuit to ground. A condition for proper operation is the requirement to connect physical grounding, as well as automatic fuses and residual current switches. Such filters and similar spark gap circuits are found on almost any equipment such as surge protectors, power supplies, inverters, usually having a physical connection to ground.

Simple surge protector device

There are two types of SF:

1. Built-in.
2. Stationary – multi-channel.

Built-in

Compact SF boards are part of the internal structure of various electronic equipment. They are equipped with computers and other complex equipment.

Built-in network filter board

The photo shows the SF device. The following parts are installed on the board:

• VHF – capacitor;
• toroidal throttle;
• additional capacitors;
• varistor;
• induction coils;
• thermal fuse.

A varistor is a resistor with variable resistance. If the standard voltage threshold (280 V) is exceeded, its resistance can decrease tens of times. The varistor performs the function of surge protection.

Stationary – multi-channel

The device body has several sockets. Thanks to this, it is possible to connect all existing electrical equipment in one room to one outlet through a filter. To remove high-frequency radio interference, a simple LC filter is used. Fireproof thermal fuses prevent power surges. Some models use disposable fuses.

Model range of Pilot network filters

The product range of the domestic company ZIS is represented by several series. They have different levels of protection and a range of functions. Pilot surge protectors are designed for consumers with varying purchasing power and meet any voltage stabilization requirements. The equipment range is represented by the following lines:

• S series;
• L series;
• GL series;
• Pro series;
• Bit series;
• T series;
• Single series.

Each line has a certain functionality and degree of protection.

Housing made of impact-resistant, flame-retardant plastic

Series S

Devices of this modification belong to the budget class and have a basic set of filtration tools. The design of this model provides the following means:

• Varistor. Designed to smooth out impulse noise. They arise when using tools and equipment whose operation is associated with the formation of a spark: drill, hammer drill, etc.
• Thermal fuse. Protects the device from overheating when the permissible power is exceeded.
• Fusible and thermal bimetallic fuses prevent short circuits from overload.

The surge protector has five Euro-type sockets with grounding contacts and one for connecting old-style plugs. Models with the designation Max differ from the basic modification by increased power up to 3.5 kW and a current of 15 A.

Advice. All ZIS products are developed taking into account all the shortcomings and parameters of domestic electrical networks. Accordingly, it is fully adapted to work in such conditions.

Series L

Has all the basic means of protection. The difference is the installation of three varistors, a filter to eliminate high-frequency capacitive-type interference. The light indication indicates the current state of the device. The body is made of high-strength and refractory plastic. The rosette group is located in one row.

GL Series

It has the same protections as the S and L series models. An inductive-capacitive filter is used to stabilize high-frequency interference. The gas discharge limiter provides protection against surges during lightning discharges. The sockets are covered with special covers to prevent electric shock to the child.

Pilot surge protector – protection at a reasonable price

Pro Series

The surge protectors in this series are premium class and have advanced protection features. Network diagnostic tools automatically determine the presence and absence of a ground loop. Diagnostics is intended for installation and subsequent stabilization of the phasing of the connected plug. The contact group is made of high-strength steel, which ensures reliable contact of contacting parts. One of the sockets is made of the Gadget Parking type, which allows you to connect one plug with round contacts or two with flat contacts at the same time. Excess cords to be connected are placed in a special holder.

Bit Series

Bit line devices have only one socket with grounding contacts, do not have an extension cord and are installed directly into the socket. This modification has all the anti-interference features of the L series models.

Series T

The design and degree of protection are similar to the Bit series. The difference lies in the number of sockets, there are 4 of them in this line, and two USB ports for charging mobile phones, smartphones, and MP3 players. The device is designed for a total connected power of 3.3 kW.

Single Series

This model is equipped with one socket with grounding contacts. The configuration and design are similar to the Bit series. The device is equipped with means of protection against the appearance of 380 V in the network. When the voltage exceeds peak limits (increase or decrease), the supply of electricity is automatically stopped and resumed when the parameter stabilizes.

ZIS products meet all GOST requirements. Each series has an optimal price/quality ratio. Due to this, Pilot surge protectors are in high demand and popularity among consumers.

Scheme of SF protection against network interference

A typical network filter circuit is the basis of all devices of this type, with the exception of additional details. The classic is connecting to the points: Ground, Phase and Zero. A varistor VDR 1 is installed at the input. It suppresses voltage surges in the mains current. With a high voltage surge, the resistance of the varistor drops sharply, thereby preventing the interference from passing further through the circuit.

To dampen small voltage changes, inductor Tr1 and three capacitors C are used. Capacitors C1, C2 and C3 are reactive radio components that constantly change the resistance level. It increases sharply when the current frequency changes.

Normal current passes through the filter unimpeded. At the same time, high-frequency interference is delayed in the SF. The filter resistance is directly proportional to the current frequency. Both indicators increase simultaneously, which makes it possible to delay interference on the way to the consumer.

Note! A three-wire power supply network may be subject to interference in the phase-zero, ground-phase, and ground-zero sections. Effective suppression of such negative phenomena is carried out by normal standard grounding of the SF

Line filter with 2 winding choke

SF based on a choke with two windings is used for sensitive audio equipment. Speakers are sensitive to power supply interference. If any occur, the speakers distort the sound and emit extraneous background noise. Radio equipment connected to the network via a SF with a 2-winding coil is protected from such interference.

The circuit is assembled on a separate printed circuit board. You will need several capacitors and a homemade inductor. It is made as follows:

1. A ring made of ferrite grade NM with a magnetic permeability from 400 to 3000 can be taken from old electrical equipment.
2. The magnetic core is wrapped in cloth and coated with varnish.
3. PEV brand wire is used for winding. Its cross-sectional area depends on the magnitude of the load. Powerful consumers require a significant increase in this parameter.
4. Winding is carried out with two wires in different directions.
5. Make 10, 12 turns of each conductor.
6. Capacitors are installed at the beginning and end of the circuit. They must withstand voltages up to 400 V.

The windings of the inductor are connected in series order. Therefore, the magnetic fields of the coil are mutually absorbed. When a high frequency current passes, the resistance of the inductor increases sharply. Capacitors absorb and short-circuit interference.

The printed circuit board is placed in a separate metal case. As a last resort, the circuit is fenced off with metal sides. This is done in order to eliminate additional interference from stray electromagnetic fields.

With each new generation of electronic equipment, increased demands are placed on the quality characteristics of the mains current. In order not to have to repair sensitive electronics, you must connect them through surge protectors. If you need to filter the current for a small number of consumers, then you can take the economical path and make a surge protector with your own hands.

Multifunctional UPS

The UPS protects devices not only during shutdown, but also when voltage drops below an acceptable threshold by switching to batteries. Intermittent operation will shorten battery life. It is advisable to additionally connect a voltage stabilizer in front of the uninterruptible power supply. For some models this is not necessary. A modern UPS may contain a built-in filter or voltage stabilizer.

The voltage of a modified (rectangular) sinusoid cannot be measured correctly with a conventional voltmeter. Readings will differ significantly from actual values.