Charger with current stabilization. A simple automatic charger Vitaly Kravtsov's electronic circuits

Recently, I had to independently build a charger for a car battery with a current of 3 - 4 amperes. Of course, there was no desire to be wiser, there was no time, and first of all I remembered the circuit of the charging current stabilizer. According to this scheme, it is very simple and reliable to make a charger.

Here is the schematic for the charger:

An old microcircuit was installed (K553UD2), although it was old, there was simply no time to try out new ones, and besides, it was at hand. The shunt from the old tester fit perfectly in place of the resistor R3. The resistor can, of course, be made from nichrome yourself, but at the same time, the cross section must be sufficient to withstand the current through itself and not heat up to the limit.

We install the shunt parallel to the ammeter, we select it taking into account the dimensions of the measuring head. Actually, we install it on the head terminal itself.

This is how the charger circuit board looks like:

Any transformer from 85 watts and above can be used. The secondary winding should be 15 volts, and the wire cross section should start from 1.8 mm (copper diameter). 26MV120A came up to the place of the rectifier bridge. It may be too big for this type of construction, but it is very easy to install it, 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 the old radio tape recorder fit me well. I drilled holes in the top cover for good airflow. Instead of the front panel, a textolite sheet 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 back wall of the radiator.

Well, we have assembled a current stabilizer, now we need to check it by shorting (+) and (-) to each other. The regulator should provide smooth adjustment over the entire range of charging current. If necessary, you can use the selection of the 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 such a charger, which will stably 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 completed.

CHARGING DEVICE FOR CAR BATTERIES

Charger circuits for car batteries are quite common and each has its own advantages and disadvantages. Most of the simplest charger circuits are built on the principle of a voltage regulator with an output node assembled on thyristors or powerful transistors. These schemes have significant drawbacks - the charge current is not constant and depends on the voltage reached on the battery. A large number of circuits do not have output short circuit protection, which leads to a breakdown of the output power elements. The proposed scheme is devoid of these shortcomings, is quite reliable (it was developed in 1995 and manufactured in an amount of about 20 copies that have never failed) and is designed to be repeated by radio amateurs of the "middle level".

The device provides a charge current of up to 6A, current and voltage control using a dial indicator, short circuit protection and automatic shutdown after a specified time using a timer. The circuit consists of a sawtooth voltage driver (transistors VT1, VT2), comparator DA1 , signal amplifier with current-sense shunt on the operational amplifier DA2 and output power thyristors VD5, VD6 , which are installed on small radiators, which can be used as a metal case of the device. The circuit is configured in several stages: 1. The amplitude of the "saw" on the variable resistor is measured with an oscilloscope R6 , which should be about 2V, otherwise the selection of a resistor R4 e e is brought to this value. Next load the shunt R18 current 6A and selection of resistors R15, R17 achieve a voltage level at input 3 of the comparator, equal to the amplitude of the sawtooth voltage (2V) - after that, the charger begins to regulate the output current normally. 2. A rechargeable battery is connected to the output of the device in series with an external reference ammeter, a value of 3 ... 6 A is set with the current regulator, and the toggle switch of the charger is switched to the "current" position. Resistor selection R14 achieve the correct current readings on the scale of the built-in device. 3. The battery is connected directly to the output of the charger and the voltage on it is monitored using an external exemplary voltmeter. Resistor selection R20 achieve the correct readings of the built-in pointer device on the voltage scale. This completes the setup. As a measuring device, you can use any available head, the linear scale of which must be prepared in advance. Shunt R18 can be made from a piece of nichrome wire with a diameter of about 2 mm and a length of about 15 cm. The accuracy of setting the resistance does not play a big role, because selection of resistors R15, R17 the required value of the output signal is set DA2 . If the thyristors are not sufficiently reliable to start, the capacitor C6 can be removed, and the resistor R11 can be replaced with a two-watt one, with a nominal value of 510 Ohm ... 1kOhm. The timer does not require a separate setting, if desired, it can be omitted - the rest of the circuit will not change. The main electronic elements are assembled on a printed circuit board.

This circuit has stood the test of time, does not contain scarce or rare elements, but over the past period, a new accessible element base has appeared, allowing you to build power supplies with higher characteristics. The circuits given on the following pages of the section have been developed relatively recently, use elements currently available and are suitable for repetition by intermediate radio amateurs:

Under certain conditions, the car battery is discharged. This can happen both due to the natural wear of the part, and due to incorrect operation. For example, if you leave your car in a parking lot over the winter, it is likely that you will need a charger to revive the car.

Attention! You can assemble a charger for a car battery with your own hands, the main thing is to do everything clearly according to the scheme.

The process of discharging the battery

Before you start restoring the device, you need to consider in detail the reason that led to this situation. The scheme of work is quite simple. The battery is charged by the generator.

To ensure that the emission of gases during charging does not exceed the permissible limits, a special relay is installed. It provides the required level of power supply. Usually this indicator is set at around 14.1 V. An error within 0.2 V is allowed.

However, in order for a car battery to be fully charged, a charger with a power output of 14.5 V is needed, its circuit is quite simple. It is not surprising that almost every motorist can make a device.

If the temperature is positive outside, then a half-charged battery can start the car. Unfortunately, in the winter in the same situation, you may have serious problems. The fact is that when the window is -20, the battery capacity is halved. Not surprisingly, in this scenario, most motorists are thinking about a battery charger circuit that could be easily assembled.

Under the influence of negative temperatures, the viscosity of the lubricant increases. The starting current also increases. As a result, starting the car without lighting will not work. Of course, it is better not to bring this to a head.

Important! Before winter, the best battery prevention will be charging with a charger that you have assembled based on one of the schemes presented in the article.

Of course, a battery charger can be purchased at the store, but its cost is not small. Perhaps it is for this reason that more and more motorists are turning to old schemes that allow you to assemble a working device with your own hands in a few hours.

About car chargers

If desired, and with some agility, you can charge the battery even with a single diode. True, for this you will also need a heater, but usually every garage has it.

The circuit for turning on such a primitive charger is quite simple. The battery is connected via a diode to the electrical network. The power of the heater can be in the range of 1-2 kilowatts. Fifteen hours of such therapy is enough to bring the battery back to life.

Important! The efficiency of the charger, whose electrical circuit consists of a heater and a diode, is only 1 percent.

If, as an alternative, we consider chargers that have transistors in their working circuits, then such devices differ in that emit a huge amount of heat. They are also at risk of short circuits. Especially expensive when using them is the error in choosing the polarity when connected to the battery contacts.

Often, when creating a charger, drivers use circuits that include thyristors. Unfortunately, they are not able to provide high stability of the current supplied to the battery.

Another significant disadvantage of thyristor charger circuits is acoustic noise. It is impossible to ignore radio interference that can affect the operation of mobile phones or other radio equipment.

Important! A ferrite ring allows you to significantly reduce radio interference from a charger with thyristors. It must be put on the network wire.

What schemes are popular on the Internet

There are many technical solutions, each of which has its pros and cons. Most often on the Internet you can find a charger circuit from a computer power supply.

There are several important nuances in such a decision. Many motorists choose this way of creating a device for recharging because the block diagrams of power supplies for computers are identical to each other. However, their electrical circuits are different. Therefore, in order to work with devices of this class, you need a specialized education. It will be quite difficult for self-taught and amateurs to cope with such work.

It is better to focus on the capacitor circuit. It has the following advantages:

1. First, it gives a relatively high efficiency.
2. Secondly, this design generates a minimum of heat.
3. Thirdly, it guarantees a stable current source.
4. The fourth indisputable advantage is pretty good protection against accidental short circuits.

Unfortunately, it was not possible to do without shortcomings. Sometimes when using this charger, there is a loss of contact with the battery. As a result, the voltage increases several times. This creates a resonant circuit. This breaks the whole circuit.

Operating schemes

General structure

Despite the apparent complexity, this structure is quite simple to create. In fact, it consists of several complete systems. If you don't feel confident in yourself that will allow you to collect it. You can eliminate some elements while retaining most of the performance.

For example, you can exclude from this figure all the elements that are responsible for automatic shutdown. This will greatly simplify the process of radio engineering work.

Important! In the overall structure, a special role is played by the electrical system, which is responsible for protection against incorrect connection of the poles.

A relay is used to protect the charger from incorrect connection of the poles. In this case, if connected incorrectly, the diode will not pass current, and the circuit will retain its performance.

Provided that all contacts are connected correctly, current flows to the terminals and the device provides power to the car battery. This type of protection system can be used with thyristor and transistor equipment.

Ballast capacitors

When you make a capacitor-type charging system, special attention should be paid to the radio engineering structure responsible for stabilizing the current strength. It is best to organize its work by connecting the primary winding T1 and capacitors C4-C9 in series.

Important! Increasing the capacitance of the capacitor allows you to achieve an increase in current power.

The figure above shows a complete electrical structure capable of charging a battery. The only thing you need is a diode bridge. Truth, It should be noted that the reliability of this system is extremely low.. The slightest violation of the contact leads to breakage of the transformer.

The value of the capacitor directly depends on the battery charge, the dependence is as follows:

• 0.5 A - 1 μF;
• 1 A - 3.4 μF;
• 2 A - 8 μF;
• 4 A - 16 μF;
• 8 A - 32 uF.

Capacitors are best connected in groups in parallel with each other. As a switch, you can use a two-gallet apparatus. Sometimes engineers use toggle switches in their circuits.

Results

There are many simple battery charger circuits. In order to make them with your own hands, you do not need any special radio engineering knowledge. Enough perseverance and desire to restore the car battery at no cost. It is most practical to use a capacitor circuit. It has high efficiency and good resistance to short circuits.

In this article, let's talk about another car charger. We will charge the batteries with a stable current. The charger circuit is shown in Figure 1.

A rewound transformer from a TS-180 tube TV is used as a network transformer in the circuit, but TS-180-2 and TS-180-2V are also suitable. To rewind the transformer, first we carefully disassemble it, not forgetting to notice which sides the core was glued together, it is impossible to confuse the position of the U-shaped parts of the core. Then all secondary windings are wound up. The shielding winding, if you use the charger only at home, can be left. If it is intended to use the device in other conditions, then the shielding winding is removed. The upper insulation of the primary winding is also removed. After that, the coils are impregnated with bakelite varnish. Of course, impregnation in production takes place in a vacuum chamber, if there are no such possibilities, then we will impregnate it in a hot way - in hot varnish, heated in a water bath, throw the coils and wait for an hour until they are impregnated with varnish. Then we let the excess varnish drain and put the coils in a gas oven with a temperature of about 100 ... 120 ° C. In extreme cases, the winding of the coils can be impregnated with paraffin. After that, we restore the insulation of the primary winding with the same paper, but also impregnated with varnish. Next, we wind on coils along ... now we will count. To reduce the no-load current, and it will obviously increase, since we do not have the necessary ferroplast for gluing twisted, split cores, we will use all the turns of the coil windings. So. The number of turns of the primary winding (see table) is 375 + 58 + 375 + 58 = 866 turns. The number of turns per volt is 866 turns divided by 220 volts, we get 3.936 ≈ 4 turns per volt.

We calculate the number of turns of the secondary winding. Let's set the voltage of the secondary winding to 14 volts, which will give us a voltage of 14 √ 2 = 19.74 ≈ 20 volts at the output of the rectifier with filter capacitors. In general, the lower this voltage, the less useless power in the form of heat will be released on the transistors of the circuit. And so, we multiply 14 volts by 4 turns per volt, we get 56 turns of the secondary winding. Now let's set the current of the secondary winding. Sometimes you need to quickly recharge the battery, which means you need to increase the charging current to the limit for a while. Knowing the overall power of the transformer - 180W and the voltage of the secondary winding, we find the maximum current 180/14 ≈ 12.86A. The maximum collector current of the KT819 transistor is 15A. The maximum power according to the reference book of this transistor in a metal case is 100W. This means that at a current of 12A and a power of 100W, the voltage drop across the transistor cannot exceed ... 100/12 ≈ 8.3 volts, and this is provided that the temperature of the transistor crystal does not exceed 25˚С. So you need a fan, since the transistor will work at the limit of its capabilities. We select a current equal to 12A, provided that in each arm of the rectifier there will already be two diodes of 10A each. According to the formula:

We multiply 0.7 by 3.46, we get the wire diameter? 2.4mm.

You can reduce the current to 10A and use a wire with a diameter of 2mm. To facilitate the thermal regime of the transformer, the secondary winding can not be covered with insulation, but simply covered with an additional layer of bakelite varnish.

Diodes KD213 are mounted on plate radiators 100 × 100x3mm made of aluminum. They can be installed directly on the metal case of the charger through mica gaskets using thermal paste. Instead of 213-x, you can use D214A, D215A, D242A, but KD2997 diodes with any letter are best suited, the typical value of the forward voltage drop of which is 0.85V, which means that at a charge current of 12A they will be released in the form of heat 0.85 12 = 10W. The maximum rectified direct current of these diodes is 30A, and they are not expensive. The LM358N chip can work with input signal voltages close to zero, I have not seen domestic analogues. Transistors VT1 and VT2 can be used with any letters. A strip of tin-plated sheet was used as a shunt. The dimensions of my strip cut out of a tin can () are 180 × 10x0.2mm. With the values ​​​​of resistors R1,2,5 indicated in the diagram, the current is regulated in the range from approximately 3 to 8A. The smaller the value of the resistor R2, the greater the stabilization current of the device. Read how to calculate the additional resistance for a voltmeter.

About the ammeter. For me, a strip cut according to the dimensions indicated above, quite by chance has a resistance of 0.0125 ohms. This means that when a current of 10A passes through it, U \u003d I R \u003d 10 0.0125 \u003d 0.125V \u003d 125mLV will fall on it. In my case, the measuring head used has a resistance of 1200 ohms at a temperature of 25°C.

Lyrical digression. Many radio amateurs, thoroughly customizing the shunts for their ammeters, for some reason never pay attention to the temperature dependence of all the elements of the circuits they assemble. You can talk on this topic indefinitely, I will give you just a small example. Here is the active resistance of the frame of my measuring head at different temperatures. And for what conditions should a shunt be calculated?

This means that the current set at home will not match the current set on the ammeter in a cold garage in winter. If you don’t care about this, then just make a switch for 5.5A and 10 ... 12A and no devices. And do not be afraid, no matter how you break them, this is another big plus of a charger with charge current stabilization.

And so on. With a loop resistance of 1200 ohms and a total deflection current of the device needle of 100 μA, we need to apply a voltage of 1200 0.0001 \u003d 0.12V \u003d 120mV to the head, which is less than the voltage drop across the shunt resistance at a current of 10A. Therefore, in series with the measuring head, put an additional resistor, preferably a tuning resistor, so as not to suffer with the selection.

The stabilizer is mounted on a printed circuit board (see photo 3). I limited the maximum charge current for myself to six amperes, so with a stabilization current of 6A and a voltage drop across a powerful transistor of 5V, the power released is 30W, and the fan blows from the computer, this radiator heats up to a temperature of 60 degrees. With a fan this is a lot, a more efficient heatsink is needed. Approximately determine the required. My advice to all of you is to install radiators designed for the operation of PP devices without coolers, let it be better that the dimensions of the device increase, but when this cooler stops, nothing will burn.

When analyzing the output voltage, its oscillogram was very noisy, which indicates the instability of the circuit, i.e. the scheme was aroused. I had to supplement the circuit with a capacitor C5, which ensured the stability of the device. Yes, also, in order to reduce the load on KT819, I reduced the voltage at the rectifier output to 18V (18 / 1.41 \u003d 12.8V, i.e. the voltage of the secondary winding of my transformer is 12.8V). Download PCB drawing. Goodbye. K.V.Yu.