The modern power supply network works in such a way that the voltage changes very often. Of course, the change in current is permissible, but in any case it should not be more than ten percent of the nominal 220 volts.
This deviation norm must be observed both in the direction of decreasing and in the direction of increasing voltage. However, such a state of the power supply network is very rare, since the current in it is characterized by large changes.
Such changes are very disliked by electrical appliances, which may not only lose their design capabilities, but may also fail. To eliminate such a negative scenario, people use various stabilizers.
Today the market offers many different models, most of which cost a lot of money. The other part cannot boast of operational reliability.
And what to do then if you don’t want to overpay or buy a low-quality product? In this situation, you can make a voltage stabilizer with your own hands.
Of course, you can make different types of stabilization devices. One of the most effective is the triac. Its actual assembly will be discussed in this article.
This stabilization device will not be sensitive to the frequency of the voltage supplied through the common network. Current equalization will be carried out provided that the input is more than 130 and less than 270 volts.
The connected devices will receive a current that is more than 205 and less than 230 volts. It will be possible to connect electrical appliances to this stabilization device, the total power of which can be equal to six kilowatts.
The stabilization device will switch the load in 10 milliseconds.
The general diagram of this stabilization device is shown in the figure:
Rice. 1. Structure of the stabilization device.
How does our network voltage stabilizer, which is easy to make with your own hands, work?
After the power is turned on, capacitor C1 is in a discharged state, transistor VT2 is open, and VT2 is closed. Transistor VT3 is also closed. It is through it that current will be supplied to each LED and triac optotron.
Since this transistor is off, the LEDs are not lit, each triac is off, and the load is off. At this time, electric current passes through resistor R1 and enters C1. Next, this capacitor is charged.
The delay interval lasts only three seconds. During this time, all transient processes are carried out, and after completion, the Schmitt trigger is triggered, the basis of which is transistors VT1 and VT2.
The voltage that comes out from the third winding T1 is rectified by the diode VD2 and capacitor C2. Next, the current passes through the divider R13…14. From R14, a voltage whose level is proportional to the number of volts in the network is included in each non-inverting input of the comparators.
The number of comparators is eight and they are all located on chips DA2 and DA3. At the same moment, a constant reference current enters the inverting input of each comparator. It is supplied by resistor dividers R15...23.
After this, the controller comes into play, which processes the signal at the input of each comparator.
When the input number of volts is less than 130, the outputs of each comparator are fixed at a low logic level. At this time, transistor VT4 is in the open state and the first LED is blinking.
He reports that the network is characterized by a very low voltage level. This means that a DIY adjustable voltage stabilizer cannot perform its function.
Each of its triacs is closed and the load is off.
When the number of input volts ranges from 130 to 150, then signals 1 and A are characterized by a high logic level. This level of all other signals is low. In this situation, transistor VT5 opens and the second LED lights up.
The optosimistor U1.2 and the triac VS2 open. It is through the latter that the load will pass. Next, it will enter the upper terminal of the winding of the automatic transformer T2.
If the input volts are in the range of 150-170 volts, then signals 2, 1 and B are characterized by a high logic level. This level of all other signals is low.
With this input number of volts, transistor VT6 opens and the third LED turns on. At this time, the second triac (VS2) opens and the current is transferred to the terminal of winding T2, which is second from the top.
A self-created voltage stabilizer that can supply 220 V will switch connections to the windings of the second transformer, provided that the input voltage level reaches 190, 210, 230 and 250 volts.
To produce such a stabilizer, you need to take a printed circuit board, which has dimensions of 115x90 millimeters. The main element from which it should be made should be one-sided foil fiberglass. The placement of elements on the board is given below.
Rice. 2. Layout of elements on the board.
Such a board can be easily printed on a laser printer. Next, use an iron. Often, the Sprint Loyout 4.0 program is used to create print files in which the layouts of such boards are stored. It is convenient to use it to make printed circuit boards.
As for transformers T1 and T2, they can be made manually.
To manufacture T1, the power of which will be designed for three kilowatts, it is necessary to prepare a magnetic circuit, the cross-sectional area of which should be 1.87 square meters. centimeters, as well as three PEV-2 wires.
The first should have a diameter of 0.064 millimeters. It is used to create the first winding. The number of its turns should be 8,669.
The other two wires are used to create the other two windings. These wires must have the same diameter, namely 0.185 millimeters. The number of turns in each winding should be 522.
Helpful advice: You can also take two ready-made transformers TPK-2-2x12V, which must be connected in series.
Connection diagram below:
Rice. 3. Connection of two transformers TPK-2-2x12V.
To create a T2 transformer with a power of 6 kilowatts, a toroidal magnetic core is used. The winding is made using PEV-2 wire. Number of turns - 455.
This transformer needs to have seven taps. The first three bends are wound using a wire that has a diameter of three millimeters. Tires are used to create the other four. Their cross-section should be 18 square millimeters. Thanks to a cross section of this size, T2 will not heat up.
Branches are made at 398, 348, 305, 266, 232 and 203 turns. The counting of turns starts from the lowest tap. In this case, the current from the network must flow through the tap of the 266th turn.
As for the other elements of the stabilizer, which you assemble yourself and which will supply constant voltage, it is better to buy them in a store.
So, you need to purchase:
Helpful advice: seven MOC3041 triac optocouplers can be replaced by MOC3061. The KR1158EN6A stabilizer can be easily replaced with KR1158EN6B. The K1401CA1 comparator is an excellent analogue of the LM339N. KTs407A can also be used as diodes.
The KR1158EN6A microcircuit must be mounted on a heat sink. To create it, an aluminum plate is taken, the area of which must exceed 15 square centimeters.
Also, triacs should be installed on the heat sink. For all seven triacs, you can use one heat sink, which must have a cooling surface. Its area must be greater than 1,600 square centimeters.
Our DIY AC voltage stabilizer must be equipped with a KR1554LP5 microcircuit, which will act as a microcontroller.
It was noted above that the device assumes the presence of nine LEDs. In the diagram presented above, they are arranged in such a way that they can fit into the corresponding holes on the front panel of the device itself.
Helpful advice: if the housing design does not allow them to be mounted as shown in the diagram, then they can also be placed on the side on which the printed conductors are located.
LEDs should be flashing.
Helpful advice: you can also use LEDs that do not blink. They should produce a red color of increased brightness. To do this, you can take L1543SRC-E or AL307KM.
Of course, it is possible to assemble simpler stabilization devices that will have their own characteristics.
If we talk about the advantages of do-it-yourself stabilization devices, the main one is lower cost. As noted above, manufacturers charge fairly high prices. Assembling your own will cost less.
Another advantage is the possibility of easy self-repair of a voltage stabilizer that was made by yourself. What is meant here is that everyone who assembled such a device understands its structure and understands the principle of operation.
If any element fails, the designer can easily locate the broken component and replace it. Easy replacement is also due to the fact that almost every element was previously purchased in a store and is easy to find in many others.
The disadvantages include the low level of reliability of such stabilizers. Enterprises have a lot of measuring and special equipment, which makes it possible to develop very high-quality models of stabilization devices.
Also, enterprises have extensive experience in creating various models and previously made mistakes are definitely corrected. This affects both the quality and reliability of factory stabilization devices.
The downside is that it's complicated to set up.
The video below shows how to assemble a stable voltage regulator, for example, to control incandescent lamps and LEDs.
Content:
In electrical circuits, there is a constant need to stabilize certain parameters. For this purpose, special control and monitoring schemes are used. The accuracy of the stabilizing actions depends on the so-called standard, with which a specific parameter, for example, voltage, is compared. That is, when the parameter value is below the standard, the voltage stabilizer circuit will turn on the control and give a command to increase it. If necessary, the opposite action is performed - to reduce.
This operating principle underlies the automatic control of all known devices and systems. Voltage stabilizers operate in the same way, despite the variety of circuits and elements used to create them.
With ideal operation of electrical networks, the voltage value should change by no more than 10% of the nominal value, up or down. However, in practice, voltage drops reach much higher values, which has an extremely negative effect on electrical equipment, even to the point of failure.
Special stabilizing equipment will help protect against such troubles. However, due to its high cost, its use in domestic conditions is in many cases economically unprofitable. The best way out of the situation is a homemade 220V voltage stabilizer, the circuit of which is quite simple and inexpensive.
You can take an industrial design as a basis to find out what parts it consists of. Each stabilizer includes a transformer, resistors, capacitors, connecting and connecting cables. The simplest is considered an alternating voltage stabilizer, the circuit of which operates on the principle of a rheostat, increasing or decreasing the resistance in accordance with the current strength. Modern models additionally contain many other functions that protect household appliances from power surges.
Among homemade designs, triac devices are considered the most effective, so this model will be considered as an example. Current equalization with this device will be possible with an input voltage in the range of 130-270 volts. Before starting assembly, you must purchase a certain set of elements and components. It consists of a power supply, rectifier, controller, comparator, amplifiers, LEDs, autotransformer, load turn-on delay unit, optocoupler switches, fuse switch. The main working tools are tweezers and a soldering iron.
To assemble a 220 volt stabilizer First of all, you will need a printed circuit board measuring 11.5x9.0 cm, which must be prepared in advance. It is recommended to use foil fiberglass as a material. The layout of the parts is printed on a printer and transferred to the board using an iron.
Transformers for the circuit can be taken ready-made or assembled yourself. Finished transformers must be brand TPK-2-2 12V and connected in series to each other. To create your first transformer with your own hands, you will need a magnetic core with a cross-section of 1.87 cm2 and 3 PEV-2 cables. The first cable is used in one winding. Its diameter will be 0.064 mm, and the number of turns will be 8669. The remaining wires are used in other windings. Their diameter will be already 0.185 mm, and the number of turns will be 522.
The second transformer is made on the basis of a toroidal magnetic core. Its winding is made of the same wire as in the first case, but the number of turns will be different and will be 455. In the second device, seven taps are made. The first three are made from wire with a diameter of 3 mm, and the rest from tires with a cross-section of 18 mm2. This prevents the transformer from heating up during operation.
It is recommended to purchase all other components ready-made in specialized stores. The basis of the assembly is the circuit diagram of a factory-made voltage stabilizer. First, a microcircuit is installed that acts as a controller for the heat sink. For its manufacture, an aluminum plate with an area of over 15 cm2 is used. Triacs are installed on the same board. The heat sink intended for installation must have a cooling surface. After this, LEDs are installed here in accordance with the circuit or on the side of the printed conductors. The structure assembled in this way cannot be compared with factory models either in terms of reliability or quality of work. Such stabilizers are used with household appliances that do not require precise current and voltage parameters.
High-quality transformers used in the electrical circuit effectively cope even with large interference. They reliably protect household appliances and equipment installed in the house. A customized filtration system allows you to deal with any power surges. By controlling the voltage, current changes occur. The limiting frequency at the input increases, and at the output it decreases. Thus, the current in the circuit is converted in two stages.
First, a transistor with a filter is used at the input. Next comes the start of work. To complete the current conversion, the circuit uses an amplifier, most often installed between resistors. Due to this, the required temperature level is maintained in the device.
The rectification circuit operates as follows. Rectification of alternating voltage from the secondary winding of the transformer occurs using a diode bridge (VD1-VD4). Voltage smoothing is performed by capacitor C1, after which it enters the compensation stabilizer system. The action of resistor R1 sets the stabilizing current on the zener diode VD5. Resistor R2 is a load resistor. With the participation of capacitors C2 and C3, the supply voltage is filtered.
The value of the output voltage of the stabilizer will depend on the elements VD5 and R1, for the selection of which there is a special table. VT1 is installed on a radiator whose cooling surface area must be at least 50 cm2. The domestic transistor KT829A can be replaced with a foreign analogue BDX53 from Motorola. The remaining elements are marked: capacitors - K50-35, resistors - MLT-0.5.
Linear stabilizers use KREN chips, as well as LM7805, LM1117 and LM350. It should be noted that the KREN symbol is not an abbreviation. This is an abbreviation of the full name of the stabilizer chip, designated as KR142EN5A. Other microcircuits of this type are designated in the same way. After the abbreviation, this name looks different - KREN142.
Linear stabilizers or DC voltage regulators are the most common. Their only drawback is the inability to operate at a voltage lower than the declared output voltage.
For example, if you need to get a voltage of 5 volts at the output of the LM7805, then the input voltage must be at least 6.5 volts. When less than 6.5V is applied to the input, a so-called voltage drop will occur, and the output will no longer have the declared 5 volts. In addition, linear stabilizers get very hot under load. This property underlies the principle of their operation. That is, voltage higher than stabilized is converted into heat. For example, when a voltage of 12V is applied to the input of the LM7805 microcircuit, then 7 of them will be used to heat the case, and only the necessary 5V will go to the consumer. During the transformation process, such strong heating occurs that this microcircuit will simply burn out in the absence of a cooling radiator.
Situations often arise when the voltage supplied by the stabilizer needs to be adjusted. The figure shows a simple circuit of an adjustable voltage and current stabilizer, which allows not only to stabilize, but also to regulate the voltage. It can be easily assembled even with only basic knowledge of electronics. For example, the input voltage is 50V, and the output is any value within 27 volts.
The main part of the stabilizer is the IRLZ24/32/44 field-effect transistor and other similar models. These transistors are equipped with three terminals - drain, source and gate. The structure of each of them consists of a dielectric metal (silicon dioxide) - a semiconductor. The housing contains a TL431 stabilizer chip, with the help of which the output electrical voltage is adjusted. The transistor itself can remain on the heatsink and be connected to the board by conductors.
This circuit can operate with input voltage in the range from 6 to 50V. The output voltage ranges from 3 to 27V and can be adjusted using a trimmer resistor. Depending on the design of the radiator, the output current reaches 10A. The capacity of smoothing capacitors C1 and C2 is 10-22 μF, and C3 is 4.7 μF. The circuit can work without them, but the quality of stabilization will be reduced. The electrolytic capacitors at the input and output are rated at approximately 50V. The power dissipated by such a stabilizer does not exceed 50 W.
Triac stabilizers work in a similar way to relay devices. A significant difference is the presence of a unit that switches the transformer windings. Instead of relays, powerful triacs are used, operating under the control of controllers.
Control of the windings using triacs is non-contact, so there are no characteristic clicks when switching. Copper wire is used to wind the autotransformer. Triac stabilizers can operate at low voltage from 90 volts and high voltage up to 300 volts. Voltage regulation is carried out with an accuracy of up to 2%, which is why the lamps do not blink at all. However, during switching, a self-induced emf occurs, as in relay devices.
Triac switches are highly sensitive to overloads, and therefore they must have a power reserve. This type of stabilizer has a very complex temperature regime. Therefore, triacs are installed on radiators with forced fan cooling. The DIY 220V thyristor voltage stabilizer circuit works in exactly the same way.
There are devices with increased accuracy that operate on a two-stage system. The first stage performs a rough adjustment of the output voltage, while the second stage carries out this process much more precisely. Thus, control of two stages is performed using one controller, which actually means the presence of two stabilizers in a single housing. Both stages have windings wound in a common transformer. With 12 switches, these two stages allow you to adjust the output voltage in 36 levels, which ensures its high accuracy.
These devices provide power primarily for low-voltage devices. This current and voltage stabilizer circuit is distinguished by its simple design, accessible element base, and the ability to smoothly adjust not only the output voltage, but also the current at which the protection is triggered.
The basis of the circuit is a parallel regulator or an adjustable zener diode, also with high power. Using a so-called measuring resistor, the current consumed by the load is monitored.
Sometimes a short circuit occurs at the output of the stabilizer or the load current exceeds the set value. In this case, the voltage across resistor R2 drops, and transistor VT2 opens. There is also a simultaneous opening of transistor VT3, which shunts the reference voltage source. As a result, the output voltage is reduced to almost zero level, and the control transistor is protected from current overloads. In order to set the exact threshold for current protection, a trimming resistor R3 is used, connected in parallel with resistor R2. The red color of LED1 indicates the protection has tripped, and the green LED2 indicates the output voltage.
After correctly assembled, the circuits of powerful voltage stabilizers are immediately put into operation; you just need to set the required output voltage value. After loading the device, the rheostat sets the current at which the protection is triggered. If the protection should operate at a lower current, for this it is necessary to increase the value of resistor R2. For example, with R2 equal to 0.1 Ohm, the minimum protection current will be about 8A. If, on the contrary, you need to increase the load current, you should connect two or more transistors in parallel, the emitters of which have equalizing resistors.
With the help of a relay stabilizer, reliable protection of instruments and other electronic devices is provided, for which the standard voltage level is 220V. This voltage stabilizer is 220V, the circuit of which is known to everyone. It is widely popular due to the simplicity of its design.
In order to properly operate this device, it is necessary to study its design and operating principle. Each relay stabilizer consists of an automatic transformer and an electronic circuit that controls its operation. In addition, there is a relay housed in a durable housing. This device belongs to the voltage booster category, that is, it only adds current in the event of low voltage.
Adding the required number of volts is done by connecting the transformer winding. Usually 4 windings are used for operation. If the current in the electrical network is too high, the transformer automatically reduces the voltage to the desired value. The design can be supplemented with other elements, for example, a display.
Thus, the relay voltage stabilizer has a very simple operating principle. The current is measured by an electronic circuit, then, after receiving the results, it is compared with the output current. The resulting voltage difference is regulated independently by selecting the required winding. Next, the relay is connected and the voltage reaches the required level.
From old tube TVs such as “Record”, “Horizon”, “Temp”, “Electron”, “Photon”, “Rainbow”, “Rubin”, “Chaika” and the like, which have long served their purpose, or rather their power transformers, you can make a fairly powerful (2-3 kW) mains voltage stabilizer. To do this, the transformers must be connected in a special way.
To begin with, we remove power transformers of the TS-180 type from old-style tube TVs. TS-200, TS-270, TS-310. (these numbers indicate the power of the transformer in watts). To do this, you need to unsolder or bite off the wires suitable for the transformer.
Next, we connect the primary windings with the filament windings in series so that the filament windings are connected in the opposite direction to the mains winding. To do this, we connect the beginning with the end. See the diagram below for an example for TS-200:
All winding designations are written on the side of the transformers, and all their terminals are marked. The stroke at the top of the number indicates the beginning of the winding.
The connected transformers should be enclosed in an insulated (wooden or plywood) box, and the terminals of the already connected transformers should be connected to the external terminals. The load is connected in series with the stabilizer.
In a similar way, you can change the power of the stabilizer - increasing or decreasing the number of power transformers.
Makedonov A.
P.S. This method will be effective if the load matches the power of the transformers. If the load is small, then we select the number and power of transformers accordingly.
This generator for low distortion audio devices generates frequencies from 1 Hz to above 65 kHz.
It can generate four different signals and the output level is adjustable from a few millivolts to 5 volts.
The generator is assembled on an inexpensive ATtiny2313 microprocessor and a 4015 CMOS chip.
Many people have a lot of soft and other toys in their home. Some make sounds, others move, and some just sit, don’t bark, don’t meow, and especially don’t walk or wink :) It’s these little friends of ours that we’ll talk about, how we can at least a little bit... “revive” our favorite toy.
An old friend of mine, a seemingly smart guy, came to visit me and somehow casually mentioned that he had bought a cool voltage stabilizer for his TV. In response to my reasonable question - why did he do this, he was surprised and immediately began to list the “indisputable” advantages of this acquisition. However, after just 15 minutes of argument, his confidence faded somewhat.
In general, it is surprising how much we are influenced by marketing ploys. Even seemingly intelligent people with developed critical thinking are easily fooled by various advertising tricks and sweet assurances from salespeople. In the case of stabilizers, I think memories from the distant past came into play - from the good old Soviet Union.
The adult generation remembers very well that in the USSR under every TV there was a plastic box called a “voltage stabilizer” that was sure to hum. The box, as a rule, was hot and necessarily heavy.
Of course, TVs could work without these boxes, but any deviation of the voltage in the outlet from 220V led to the image on the screen changing its brightness and saturation, and the picture itself changing in size. So almost everyone had stabilizers.
Such stabilizers worked using the principle of supersaturation of the transformer core and therefore they were designed for a narrow range of load power.
For black-and-white TVs with a power of 100-200 W, some models of stabilizers were produced, and for color TVs - completely different, more powerful ones. It was impossible to include a low-power load in a powerful stabilizer, because in this case, the very principle of its operation was violated and it ceased to perform its function.
Here, for example, is an excerpt from the instruction manual for the Soviet Vega-9 voltage stabilizer:
Allowable stabilizer output power:
— minimum 100,
— maximum 200 W.Allowable input voltage fluctuations are 154…253 V.
Stabilized output voltage 198…231 V.Efficiency - 84%.
Stabilizer weight 3.4 kg.
As you can see, there was a limitation on the load power from below, i.e. It was impossible to turn on a small black-and-white TV with a power of less than 100 W in such a stabilizer. More precisely, it was possible to turn it on, but in this case one could forget about any voltage stabilization.
If you plug a load of more than 200W into Vega-9 (for example, a color TV of those times), then the stabilizer is guaranteed to overheat and the plastic case begins to melt and stink. I have seen such melted boxes from other people more than once.
By the way, today such old stabilizers for old TVs are called ferroresonant. Today's devices are often assembled using an autotransformer circuit with a large number of taps and triac switching between them.
All modern household appliances, including TVs of the 3rd generation and newer, have switching power supplies capable of operating in a wide range of input voltages.
On imported TV models released after 2000, something like 110-260V AC is usually written on the back cover. At the same time, a stable voltage is always maintained at the output of such a power supply, which powers all components of the TV.
So, if your TV was manufactured after 1985 (not to mention models from 2017), then it does not need a stabilizer at all. Leave it in the store.
And don’t listen to the convincing assurances of TV sellers that a stabilizer for your new TV is simply absolutely necessary. The seller has only one task - to sell you as many extras as possible for your TV.
He will tell you tales about how LCD TVs “burn out pixels” from power surges, how LED TVs burn out LEDs, how stabilizers protect your TV from short circuits, interference, direct hits from nuclear weapons, and other nonsense. Don't listen!
A short circuit will do absolutely nothing to your TV (unless, of course, the short circuit occurs in the TV itself). In the event of a short circuit somewhere on the line, the current will simply flow along a different path and the TV will be de-energized (i.e. it will simply turn off). That's all the terrible and terrible consequences of short circuit.
A about pixel burnout I have the following to say. Firstly, the “pixels” themselves do not burn out at all; the control transistors that “light up” these same pixels fail. If the transistor burns out, the pixel remains extinguished forever (black dot), and if the transistor breaks, then the pixel always glows (bright dot on the screen).
The most interesting thing is that it doesn’t matter whether you have a stabilizer or not, pixels can and will fly out. This happens simply according to the theory of system reliability (just imagine how many of them there are, these pixels!).
Since we are talking about pixels, this means that this is an LCD TV, which means it has a switching power supply, therefore, voltage surges in the network do not have any effect on the voltage in the TV circuit itself.
In this way, voltage stabilization is already carried out inside the TV circuit, therefore, buying another stabilizer is nothing more than a waste of money.
You may ask, what happens if the voltage in the network goes beyond the permissible values indicated on the TV nameplate? It's simple. If the voltage gets too low, The TV will simply turn off. Without consequences. After the voltage returns to normal values, the TV can be turned on again as usual.
Worse, if the voltage gets too high. Then a breakdown of a special element at the TV input - a varistor - will occur. A broken varistor causes a real short circuit, as a result of which the fuse blows and the circuit is de-energized. This is overvoltage protection. After some time, the varistor returns to normal; all that remains is to replace the fuse. By the way, self-resetting fuses are now used.
So, as you can see, a modern TV provides protection against all major dangers. There is absolutely no point in buying a stabilizer specifically for TV.
The only thing your TV may need is good surge protector. And even then only in some cases. All switching power supplies already contain an RF filter at the input (this, by the way, is done to ensure that high-frequency interference from a working pulse generator does not penetrate the network and interfere with the operation of other electrical devices), but sometimes it is still not enough. And then an external surge filter will help get rid of interference.
However, here you need to be sure that interference penetrates into the TV through the power supply circuits, and not through the antenna, for example. In the latter case, the surge protector will be completely useless; it is better to focus on finding a high-quality antenna with good side-lobe suppression.
Particularly cunning sellers manage to sell gullible customers in addition to the TV uninterruptible power supply. But you and I are smart, we know that uninterruptible power supplies are designed to maintain the functionality of equipment in the event of a power outage. They are indispensable for devices such as desktop computers, some medical equipment, network equipment from providers, etc. But why do TVs need uninterruptible power supplies?! So that you can finish watching the comedy club or what? A very dubious waste of money.
Thus, we have convincingly proven that for any modern TV - be it an LED TV or just an LCD TV - voltage stabilizers are absolutely unnecessary devices (as well as uninterruptible power supplies and, in most cases, surge protectors).
Now the answer to the question - is a voltage stabilizer needed for a TV, I think, is obvious. Just plug your TV into a power outlet and enjoy watching!
I recently had to build my own charger for a car battery with a current of 3 - 4 amperes. Of course, I didn’t want to split hairs, I didn’t have time, and first of all I remembered the charging current stabilizer circuit. Using this scheme it is very simple and reliable to make a charger.
Here is the circuit diagram for the charger:
An old microcircuit (K553UD2) was installed, although it was old, there was simply no time to try new ones, and besides, it was at hand. The shunt from the old tester fit perfectly in place of resistor R3. The resistor can, of course, be made from nichrome yourself, but the cross-section must be sufficient to withstand the current through it and not heat up to the limit. 
We install the shunt parallel to the ammeter, select it taking into account the dimensions of the measuring head. Actually, we install it on the head terminal itself.
This is what the charger current stabilizer circuit board looks like:
Any transformer can be used from 85 W and above. The secondary winding should have a voltage of 15 volts, and the wire cross-section should start from 1.8 mm (copper diameter). A 26MV120A took the place of the rectifier bridge. It may be too big for this type of design, but it is very easy to install, just screw it on and put on the terminals. You can install any diode bridge. For him, the main task is to withstand the appropriate current.
The case can be made from anything; the case from an old radio tape recorder worked well for me. For good air passage, I drilled holes on the top cover. Instead of the front panel, a sheet of PCB was installed. The shunt, the one on the ammeter, must be adjusted based on the readings of the test ammeter.
We attach a transistor to the rear wall of the radiator.
Well, we have assembled the current stabilizer, now we need to check it by short-circuiting (+) and (-) together. The regulator should provide smooth adjustment over the entire range of charging current. If necessary, you can use the selection of resistor R1.
It is important to remember that all the voltage goes to the control transistor and it gets very hot! Once checked, open the jumper!
Everything is ready and you can now use a charger that will consistently maintain current throughout the entire charging range. It is necessary to monitor the voltage reading on the battery using a voltmeter, since such a charger does not have an automatic shutdown after charging is complete.
