We make our own car battery chargers. Scheme for the manufacture of a charger for a battery from a transformer Which transformer is needed for a charger

Now it makes no sense to assemble a charger for car batteries on your own: there is a huge selection of ready-made devices in stores, their prices are reasonable. However, let's not forget that it's nice to do something useful with your own hands, especially since a simple charger for a car battery can be assembled from improvised parts, and its price will be a penny.

The only thing to immediately warn about is that circuits without precise adjustment of the current and output voltage, which do not have a current cutoff at the end of the charge, are suitable for charging only lead-acid batteries. For AGM and the use of such chargers damages the battery!

How to make a simple transformer device

The circuit of this charger from a transformer is primitive, but workable and is assembled from available parts - factory chargers of the simplest type are designed in the same way.

At its core, this is a full-wave rectifier, hence the requirements for the transformer: since the voltage at the output of such rectifiers is equal to the nominal AC voltage multiplied by the root of two, then at 10V on the transformer winding we will get 14.1 V at the charger output. Any diode bridge is taken with a direct current of more than 5 amperes, or it can be assembled from four separate diodes, and a measuring ammeter is selected with the same current requirements. The main thing is to place it on a radiator, which in the simplest case is an aluminum plate with an area of at least 25 cm2.

The primitiveness of such a device is not only a minus: due to the fact that it has neither adjustment nor automatic shutdown, it can be used to “resuscitate” sulfated batteries. But we must not forget about the lack of protection against polarity reversal in this circuit.

The main problem is where to find a transformer of suitable power (at least 60 W) and with a given voltage. Can be used if a Soviet incandescent transformer turns up. However, its output windings have a voltage of 6.3V, so you will have to connect two in series, unwinding one of them so that you get a total of 10V at the output. An inexpensive transformer TP207-3 is suitable, in which the secondary windings are connected as follows:

At the same time, we unwind the winding between terminals 7-8.

Simple electronic charger

However, you can do without rewinding by supplementing the circuit with an electronic output voltage regulator. In addition, such a scheme will be more convenient in garage applications, as it will allow you to adjust the charge current during supply voltage drops, it is also used for small-capacity car batteries if necessary.

The role of the regulator here is performed by the composite transistor KT837-KT814, the variable resistor regulates the current at the output of the device. When assembling the charge, the 1N754A zener diode can be replaced with the Soviet D814A.

The circuit of the regulated charger is simple to repeat, and is easily assembled by surface mounting without the need for PCB etching. However, keep in mind that field-effect transistors are placed on a radiator, the heating of which will be noticeable. It is more convenient to use an old computer cooler by connecting its fan to the charger outlets. Resistor R1 must have a power of at least 5 W, it is easier to wind it from nichrome or fechral on your own or connect 10 one-watt resistors of 10 ohms in parallel. You can not put it, but we must not forget that it protects the transistors in the event of a short circuit.

When choosing a transformer, focus on the output voltage of 12.6-16V, take either an incandescent transformer by connecting two windings in series, or select a ready-made model with the desired voltage.

Video: The simplest battery charger

Alteration of the charger from the laptop

However, you can do without looking for a transformer if you have an unnecessary laptop charger at hand - with a simple alteration, we will get a compact and lightweight switching power supply that can charge car batteries. Since we need to get a voltage at the output of 14.1-14.3 V, no ready-made power supply will work, but the conversion is simple.
Let's look at a section of a typical scheme, according to which devices of this kind are assembled:

In them, maintaining a stabilized voltage is carried out by a circuit from a TL431 microcircuit that controls an optocoupler (not shown in the diagram): as soon as the output voltage exceeds the value set by resistors R13 and R12, the microcircuit lights up the optocoupler LED, informs the PWM controller of the converter a signal to reduce the duty cycle of the supplied to the pulse transformer. Difficult? In fact, everything is easy to make with your own hands.

Having opened the charger, we find not far from the TL431 output connector and two resistors connected to the Ref leg. It is more convenient to adjust the upper arm of the divider (in the diagram - resistor R13): by reducing the resistance, we reduce the voltage at the output of the charger, increasing it - we raise it. If we have a 12 V charger, we need a resistor with a large resistance, if the charger is 19 V, then with a smaller one.

Video: Charging for car batteries. Protection against short circuit and polarity reversal. DIY

We solder the resistor and instead install a trimmer, pre-configured by the multimeter for the same resistance. Then, having connected a load (a light bulb from a headlight) to the output of the charger, we turn it on and smoothly rotate the trimmer engine, while simultaneously controlling the voltage. As soon as we get a voltage in the range of 14.1-14.3 V, we turn off the memory from the network, fix the trimming resistor engine with varnish (at least for nails) and assemble the case back. It will take no more time than you spent reading this article.

There are also more complex stabilization schemes, and they can already be found in Chinese blocks. For example, here the optocoupler is controlled by the TEA1761 chip:

However, the setting principle is the same: the resistance of the resistor soldered between the positive output of the power supply and the 6th leg of the microcircuit changes. In the above diagram, two parallel resistors are used for this (thus, a resistance that is out of the standard series is obtained). We also need to solder a trimmer instead of them and adjust the output to the desired voltage. Here is an example of one of these boards:

By dialing, you can understand that we are interested in a single resistor R32 on this board (circled in red) - we need to solder it.

Similar recommendations are often found on the Internet on how to make a homemade charger from a computer power supply. But keep in mind that all of them are essentially reprints of old articles from the beginning of the 2000s, and such recommendations are not applicable to more or less modern power supplies. It is no longer possible to simply raise the 12 V voltage to the desired value in them, since other output voltages are also controlled, and they will inevitably “float away” with this setting, and the power supply protection will work. You can use laptop chargers that produce a single output voltage, they are much more convenient for rework.

The diagram of the charger for car batteries is shown in the figure. As a power transformer, I usually used network transformers from old TVs, such as the TS-180. All secondary windings are removed from the transformer coils, and all turns of the primary winding of the transformer are used as the primary for 220 volts.

Example.

The TS-180 transformer has a total number of turns of the primary winding W1 = 866 = 375+58+375+58. The greater the number of turns, the lower the no-load current of the transformer, the less noticeable the consequences of voltage surges in the primary network, so I always use the maximum possible number of turns.
Next, we find the number of turns per volt W1 / 220V = 866/220 = 4 turns. To obtain 24V in the secondary winding of the transformer, we need to wind W2 = 24 × 4 = 96 turns i.e. 48 turns on each coil and subsequently connect these coils in phase in series. In this case, the diameter of the wire of the secondary winding is equal to B \u003d 0.7 roots from the current of the transformer winding. Since with half-wave rectification there is a constant component in the secondary winding, which additionally contributes to the heating of the transformer, it is not worth choosing a wire diameter of less than two millimeters. In the absence of a thick wire, it is fashionable to wind each coil with 96 turns and connect them in-phase in parallel. In this case, the diameter of the wire must be recalculated.

For the secondary winding, we chose a wire with a diameter of 2mm. In this case, its cross-sectional area will be S₁ = π∙R² = π∙D²/4 = 3.14mm².
We find the cross-sectional area of the new wire S₂ = 3.14/2 = 1.57mm².
We calculate the diameter of this wire D ≈ 1.41 mm.

Data on other network transformers from TVs can be found here

Resistor R2 is a 21W car light bulb. It acts as a load for the discharge current between charging current pulses. Instead of a light bulb, you can use a PEV-25 resistor with a resistance of about 30 ohms.
The diode in the control electrode circuit of the thyristor can be used from any rectifier of an old TV. Variable resistor - it would be better to wire.

There are quite a few old tube TVs with serviceable power transformers. With some refinement, they can be used in chargers (memory).

On the site of the radiochip, we will consider an example of calculating this method. Of greatest interest for this purpose are televisions with a screen size of 61 cm (59 cm) for black and white and color images, in which transformers of the following types are used: TC-160, TC-180, TC-200, TCA-270, etc. Structurally, they are made of two bolted U-shaped halves of pressed electrical steel.

The dismantling of transformers should be carried out carefully so as not to damage the primary windings. The wires supplied to them are preliminarily bitten off or soldered. Bolted connection is disassembled and removed. Then the halves of the core are removed. If it is difficult to separate them due to gluing on the inside, it is recommended to lightly tap on their protruding roundings. From the frame (each separately) the secondary windings are wound up to the screen, made in the form of an open strip of foil or a single-row winding with one tap. The calculation of the diameter of the wire of the secondary winding for the charger is carried out according to the formula:

Where I is the rated current of the winding, A; Npr - the number of parallel wires (in the absence of one wire of the estimated diameter); j - current density, A / mm² (with a transformer power of 100 ... 500VA - 2.5 ... 3.5A / mm²). For example, for the TS-180 transformer, j = 2.7 A / mm² can be taken. The number of turns depends on the required voltage and the turn/V ratio (w/U) determined by the type of transformer. For a 12 V battery, depending on the charging circuit, the winding voltage is 16 ... 18 V.

The w/U ratio can be determined experimentally by winding, for example, 10 turns of wire of arbitrary diameter on any of the transformer coil frames. Then the transformer is assembled, voltage is applied to the primary winding and the voltage on the auxiliary winding is measured, which is divided by the number of turns. The number of turns per volt can be determined by counting the number of turns of the secondary winding when it is unwound (you must first measure the voltage across it from the whole transformer).

In simple ones, taps are often made from the secondary winding to make it easier to regulate the charging current. They are switched by means of a rotary switch. The current consumed by the secondary winding must not exceed the overall power of the transformer, i.e. for TS-180 at a voltage of 18V, the current is not more than 10A.

Diodes for a bridge rectifier are selected based on an allowable current equal to half the maximum charge. An ammeter and a voltmeter are used as charging mode indicators. You can get by with one milliammeter by switching it with an additional switch (the switch must withstand the charging current).

As measuring instruments, you can use recording level indicators from old tape recorders (types M370, M476, etc.) with total deviation currents of 200 ... 250 μA, providing them with appropriate shunts. Instead of measuring heads, LEDs with selected ballast resistors are also suitable. The mode is controlled by the brightness of their glow.

Not every car owner has in his garage battery charger. This article describes the steps for creating a high-quality do-it-yourself charger, in which you can adjust the output voltage, and work in several battery charge modes. Charger circuit very simple and reliable.

Every novice radio amateur able to create such a necessary device. The charger uses a transformer with an output power of 200 - 300 watts.

You can use a transformer from a Soviet tube TV, since its core has two identical windings designed for a voltage of 6-7 V and a current of 10 A. In order to get the output voltage of 12-24 V, which is necessary to charge the battery, you need to connect the windings in series . The electrical circuit shown in this article uses a 400 watt transformer.

The network winding of the transformer has a wire cross section of 0.5 mm and contains 500 turns. It is necessary to wind the turns on the core carefully, turn to turn. Every 100 turns, thick paper insulation must be installed. The secondary winding is wound with a wire with a diameter of 1.5-3 mm. 4-5 turns at an operating frequency of 50 Hz provide 1 V power.

So need winding a winding at 18 V is about 90 turns. We have already dealt with the transformer, the turn of the electronic part of the charger has come. The diode bridge is very powerful. The diodes used in the circuit are taken from the car's generator, they must be installed on the radiator, and the structure must be cooled. Overheating of diodes is strictly not allowed.

The KT819 transistor must be taken in a metal case. Instead of KT819, you can use KT814, but only as a last resort. This element of the electrical circuit is also installed on the radiator. We select a variable resistor for the circuit based on the required resistance of 150 ohms and a rated operating power of 5 watts.

For such purposes a thyristor of domestic production KU202N, or another analogue, is well suited. A variable resistor regulates the desired output voltage, which allows the device to operate in several modes: fast charging - 18 V, medium charging - 16 V, moderate charging - 14 V.

The device must be equipped with a cooler. For these purposes, a cooler from a computer power supply is perfect. Cooling of the transformer is necessary, since the turns of the secondary winding are made of aluminum, and in the process of fast charging the battery can overheat. The fan is directly connected to the output of the charger, its speed increases with the set charging voltage.

One of the main tools at hand in the laboratory of a radio amateur is, of course, a power supply, and as you know, the basis of most power supplies is a power voltage transformer. Sometimes excellent transformers fall into our hands, but after checking the windings, it becomes clear that the voltage we need is not available due to the burnout of the primary or secondary. There is only one way out of this situation - to rewind the transformer and wind the secondary winding with your own hands. In amateur radio technology, you usually need to have a voltage of 0 to 24 volts to power a variety of devices.

Since the power supply will operate from a 220 volt household network, when carrying out small calculations, it becomes clear that on average, every 4-5 turns in the secondary winding of the transformer give a voltage of 1 volt.

How to make a DIY car battery charger?

This means that for a power supply with a maximum voltage of 24 volts, the secondary winding should contain 5 * 24, in total we get 115-120 turns. For a powerful power supply, you also need to select a wire of the required cross section for rewinding; on average, the wire diameter is chosen for a medium-power power supply is 1 millimeter (from 0.7 to 1.5 mm).

To create a powerful power supply, you need to have a powerful transformer at hand, a transformer from a black-and-white TV made in the Soviet Union is perfect. The transformer must be disassembled, the hearts (pieces of iron) removed and all the secondary windings unwound, leaving only the network winding, the whole process takes no more than 30 minutes.

Next, we take the indicated wire and wind it on the transformer frame with the calculation of 5 turns of 1 volt. Thus, you can assemble with your own hands, for example, a charger for a car battery, to charge a car battery, the secondary winding must contain 60-70 turns (the charging voltage must be at least 14 volts, the current strength is 3-10 amperes), then you need a powerful diode bridge for rectification AC and you're done.

But to charge a car battery, the secondary winding wire of the transformer must be selected with a diameter of at least 1.5 millimeters (from 1.5 to 3 millimeters to have a charging current of 3 to 10 amperes). In the same way, you can design a welding machine and other power devices.

DIY 12v battery charger

I made this charger for charging car batteries, the output voltage is 14.5 volts, the maximum charge current is 6 A. But it can also charge other batteries, such as lithium-ion, since the output voltage and output current can be adjusted over a wide range. The main components of the charger were purchased from the Aliexpress website.

These are the components:

You will also need an electrolytic capacitor 2200 uF at 50 V, a transformer for the TS-180-2 charger (see how to unsolder the TS-180-2 transformer in this article), wires, a power plug, fuses, a radiator for a diode bridge, crocodiles. You can use another transformer with a power of at least 150 W (for a charging current of 6 A), the secondary winding must be rated for a current of 10 A and produce a voltage of 15 - 20 volts. The diode bridge can be assembled from individual diodes rated for a current of at least 10A, for example, D242A.

The wires in the charger should be thick and short.

How to charge a car battery

The diode bridge must be fixed to a large radiator. It is necessary to increase the radiators of the DC-DC converter, or use a fan for cooling.

Diagram of a charger for a car battery

Charger Assembly

Connect the cord with a power plug and a fuse to the primary winding of the TC-180-2 transformer, install the diode bridge on the radiator, connect the diode bridge and the secondary winding of the transformer. Solder the capacitor to the positive and negative terminals of the diode bridge.

Connect the transformer to a 220 volt network and measure the voltage with a multimeter. I got these results:

The alternating voltage at the terminals of the secondary winding is 14.3 volts (mains voltage is 228 volts).
DC voltage after diode bridge and capacitor 18.4 volts (no load).

Based on the diagram, connect a step-down converter and a voltammeter to the DC-DC diode bridge.

Setting the output voltage and charging current

Two trimming resistors are installed on the DC-DC converter board, one allows you to set the maximum output voltage, the other can set the maximum charging current.

Plug the charger into the mains (nothing is connected to the output wires), the indicator will show the voltage at the output of the device, and the current is zero. Set the voltage potentiometer to 5 volts at the output. Close the output wires between each other, set the short circuit current to 6 A with the current potentiometer. Then eliminate the short circuit by disconnecting the output wires and the voltage potentiometer, set the output to 14.5 volts.

Reverse polarity protection

This charger is not afraid of a short circuit at the output, but it can fail if the polarity is reversed. To protect against polarity reversal, a powerful Schottky diode can be installed in the gap of the positive wire going to the battery. Such diodes have a low voltage drop when connected directly. With such protection, if you reverse the polarity when connecting the battery, no current will flow. True, this diode will need to be installed on the radiator, since a large current will flow through it when charging.

Suitable diode assemblies are used in computer power supplies. In such an assembly there are two Schottky diodes with a common cathode, they will need to be paralleled. Diodes with a current of at least 15 A are suitable for our charger.

It should be borne in mind that in such assemblies the cathode is connected to the case, so these diodes must be installed on the radiator through an insulating gasket.

It is necessary to adjust the upper voltage limit again, taking into account the voltage drop across the protection diodes. To do this, the voltage potentiometer on the DC-DC converter board must be set to 14.5 volts measured with a multimeter directly at the output terminals of the charger.

How to charge the battery

Wipe the battery with a rag soaked in a solution of soda, then dry. Unscrew the plugs and check the electrolyte level, if necessary, add distilled water. Plugs must be turned out during charging. Debris and dirt must not get inside the battery. The room in which the battery is charged must be well ventilated.

Connect the battery to the charger and plug the device into the mains. During charging, the voltage will gradually increase to 14.5 volts, the current will decrease over time. The battery can be conditionally considered charged when the charging current drops to 0.6 - 0.7 A.

DC-DC buck converter TC43200 - product link.

An overview of the DC-DC CC CV TC43200 buck converter.

The device can be used to recharge car batteries with a capacity of up to 100 Ah, to charge motorcycle batteries in a mode close to optimal, and also (with a simple modification) as a laboratory power supply.

The charger is based on a push-pull transistorized voltage converter with autotransformer coupling and can operate in two modes - a current source and a voltage source. When the output current is less than a certain limit value, it works as usual - in the voltage source mode. If you try to increase the load current above this value, the output voltage will decrease sharply - the device will switch to the current source mode.

DIY car battery chargers

The mode of the current source (having a large internal resistance) is provided by the inclusion of a ballast capacitor in the primary circuit of the converter.

Schematic diagram of the charger is shown in fig. 2.94.

Rice. 2.94.Schematic diagram of a charger with a quenching capacitor in the primary circuit.

The mains voltage through the ballast capacitor C1 is supplied to the rectifier bridge VD1. Capacitor C2 smooths out the ripple, and the zener diode VD2 stabilizes the rectified voltage. The zener diode VD2 simultaneously protects the converter transistors from overvoltage at idle, as well as when the device output is closed, when the voltage at the output of the VD1 bridge rises. The latter is due to the fact that when the output circuit is closed, the generation of the converter can be disrupted, while the load current of the rectifier decreases, and its output voltage increases. In such cases, the zener diode VD2 limits the voltage at the output of the bridge VD1.

The voltage converter is assembled on transistors VT1, VT2 and transformer T1. The converter operates at a frequency of 5 ÷ 10 kHz.

Diode bridge VD3 rectifies the voltage taken from the secondary winding of the transformer. Capacitor C3 - smoothing.

The experimentally taken load characteristic of the charger is shown in fig. 2.95. With an increase in load current to 0.35 ÷ 0.4 A, the output voltage changes slightly, and with a further increase in current, it sharply decreases. If an undercharged battery is connected to the output of the device, the voltage at the output of the bridge VD1 decreases, the zener diode VD2 exits the stabilization mode and, since capacitor C1 with a large reactance is included in the input circuit, the device operates in the current source mode.

If the charging current has decreased, then the device smoothly switches to the voltage source mode. This makes it possible to use the charger as a low-power laboratory power supply. When the load current is less than 0.3 A, the level of ripple at the operating frequency of the converter does not exceed 16 mV, and the output resistance of the source decreases to a few ohms. The dependence of the output resistance on the load current is shown in fig. 2.95.

Rice. 2.95. Load characteristic of a charger with a quenching capacitor in the primary circuit.

Setting up a charger with a quenching capacitor in the primary circuit

Adjustment begins with checking the correct installation. Then they make sure that the device is working when the output circuit is closed. The closing current must be at least 0.45 0.46 A. Otherwise, resistors R1, R2 should be selected in order to ensure reliable saturation of transistors VT1, VT2. A larger closing current corresponds to a smaller resistance of the resistors.

If it is necessary to use a device for charging small-sized batteries with a capacity of up to units of ampere-hours and regenerating galvanic cells, it is advisable to provide adjustment of the charging current. To do this, instead of one capacitor C1, a set of capacitors of a smaller capacity, switched by a switch, should be provided. With sufficient accuracy for practice, the maximum charging current - the closing current of the output circuit - is proportional to the capacitance of the ballast capacitor (at 4 μF, the current is 0.46 A).

If you need to reduce the output voltage of the laboratory power supply, it is enough to replace the Zener diode VD2 with another one with a lower stabilization voltage.

Transformer T1 is wound on an annular magnetic circuit of size K40x25x11 made of ferrite 1500NM1. The primary winding contains 2 × 160 turns of wire PEV-2 0.49, the secondary - 72 turns of wire PEV-2 0.8. The windings are insulated between each other with two layers of varnished fabric.

Mount VD2 zener diode on a heat sink with a usable area of 25 cm 2

Converter transistors do not need additional heat sinks, since they operate in the key mode.

Capacitor C1 - paper, designed for a rated voltage of at least 400 V.