Homemade chargers for car batteries: a simple diagram. Charger for a car battery Do-it-yourself charger circuits for car batteries

Compliance with the operating mode of rechargeable batteries, and in particular the charging mode, guarantees their trouble-free operation throughout their entire service life. Batteries are charged with a current, the value of which can be determined by the formula

where I is the average charging current, A., and Q is the nameplate electric capacity of the battery, Ah.

A classic car battery charger consists of a step-down transformer, a rectifier and a charging current regulator. Wire rheostats (see Fig. 1) and transistor current stabilizers are used as current regulators.

In both cases, these elements generate significant thermal power, which reduces the efficiency of the charger and increases the likelihood of its failure.

To regulate the charging current, you can use a store of capacitors connected in series with the primary (mains) winding of the transformer and acting as reactances that dampen excess network voltage. A simplified version of such a device is shown in Fig. 2.

In this circuit, thermal (active) power is released only on the diodes VD1-VD4 of the rectifier bridge and the transformer, so the heating of the device is insignificant.

The disadvantage in Fig. 2 is the need to provide a voltage on the secondary winding of the transformer one and a half times greater than the rated load voltage (~ 18÷20V).

The charger circuit, which provides charging of 12-volt batteries with a current of up to 15 A, and the charging current can be changed from 1 to 15 A in steps of 1 A, is shown in Fig. 3.

It is possible to automatically turn off the device when the battery is fully charged. It is not afraid of short-term short circuits in the load circuit and breaks in it.

Switches Q1 - Q4 can be used to connect various combinations of capacitors and thereby regulate the charging current.

The variable resistor R4 sets the response threshold of K2, which should operate when the voltage at the battery terminals is equal to the voltage of a fully charged battery.

In Fig. Figure 4 shows another charger in which the charging current is smoothly regulated from zero to the maximum value.

The change in current in the load is achieved by adjusting the opening angle of the thyristor VS1. The control unit is made on a unijunction transistor VT1. The value of this current is determined by the position of the variable resistor R5. The maximum battery charging current is 10A, set with an ammeter. The device is provided on the mains and load side with fuses F1 and F2.

A version of the charger printed circuit board (see Fig. 4), 60x75 mm in size, is shown in the following figure:

In the diagram in Fig. 4, the secondary winding of the transformer must be designed for a current three times greater than the charging current, and accordingly, the power of the transformer must also be three times greater than the power consumed by the battery.

This circumstance is a significant drawback of chargers with a current regulator thyristor (thyristor).

Note:

The rectifier bridge diodes VD1-VD4 and the thyristor VS1 must be installed on radiators.

It is possible to significantly reduce power losses in the SCR, and therefore increase the efficiency of the charger, by moving the control element from the circuit of the secondary winding of the transformer to the circuit of the primary winding. such a device is shown in Fig. 5.

In the diagram in Fig. 5 control unit is similar to that used in the previous version of the device. SCR VS1 is included in the diagonal of the rectifier bridge VD1 - VD4. Since the current of the primary winding of the transformer is approximately 10 times less than the charging current, relatively little thermal power is released on the diodes VD1-VD4 and the thyristor VS1 and they do not require installation on radiators. In addition, the use of an SCR in the primary winding circuit of the transformer made it possible to slightly improve the shape of the charging current curve and reduce the value of the current curve shape coefficient (which also leads to an increase in the efficiency of the charger). The disadvantage of this charger is the galvanic connection with the network of elements of the control unit, which must be taken into account when developing the design (for example, use a variable resistor with a plastic axis).

A version of the charger printed circuit board in Figure 5, measuring 60x75 mm, is shown in the figure below:

Note:

The rectifier bridge diodes VD5-VD8 must be installed on radiators.

In the charger in Figure 5 there is a diode bridge VD1-VD4 type KTs402 or KTs405 with the letters A, B, C. Zener diode VD3 type KS518, KS522, KS524, or made up of two identical zener diodes with a total stabilization voltage of 16÷24 volts (KS482, D808 , KS510, etc.). Transistor VT1 is unijunction, type KT117A, B, V, G. The diode bridge VD5-VD8 is made up of diodes, with a working current not less than 10 amperes(D242÷D247, etc.). The diodes are installed on radiators with an area of ​​at least 200 sq.cm, and the radiators will become very hot; a fan can be installed in the charger case for ventilation.

Now there is no point in assembling a charger for car batteries yourself: there is a huge selection of ready-made devices in stores, and 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 scrap parts, and its price will be a pittance.

The only thing worth warning about right away is that circuits without precise regulation of the output current and voltage, which do not have a current cutoff at the end of charging, are suitable for charging only lead-acid batteries. For AGM and the use of such charges leads to damage to the battery!

How to make a simple transformer device

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

At its core, it is a full-wave rectifier, hence the requirements for the transformer: since the voltage at the output of such rectifiers is equal to the rated AC voltage multiplied by the root of two, then with 10V on the transformer winding we get 14.1V at the output of the charger. You can take any diode bridge with a direct current of more than 5 amperes or assemble it from four separate diodes; a measuring ammeter is also 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 disadvantage: due to the fact that it has neither adjustment nor automatic shutdown, it can be used to “reanimate” 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 filament transformer turns up. However, its output windings have a voltage of 6.3V, so you will have to connect two in series, winding 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 electronically regulated charger

However, you can do without rewinding by adding an electronic output voltage stabilizer to the circuit. In addition, such a circuit will be more convenient for garage use, since it will allow you to adjust the charge current during power supply voltage drops; it is also used for small-capacity car batteries, if necessary.

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

The variable charger circuit is easy to replicate and can be easily assembled without the need to etch the printed circuit board. 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 outputs of the charger. Resistor R1 must have a power of at least 5 W; it is easier to wind it from nichrome or fechral yourself or connect 10 one-watt 10 ohm resistors in parallel. You don’t have to install it, but we must not forget that it protects the transistors in the event of a short circuit.

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

Video: The simplest battery charger

Remaking a laptop charger

However, you can do without searching for a transformer if you have an unnecessary laptop charger at hand - with a simple modification we will get a compact and lightweight switching power supply capable of charging car batteries. Since we need to get an output voltage 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 circuit according to which devices of this kind are assembled:

In them, maintaining a stabilized voltage is carried out by a circuit from the TL431 microcircuit that controls the 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, tells 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 do with your own hands.

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

Video: Charging for car batteries. Protection against short circuit and reverse polarity. With your own hands

We unsolder the resistor and instead install a trimmer, pre-set on the multimeter to the same resistance. Then, having connected a load (a light bulb from a headlight) to the output of the charger, we turn it on to the network and smoothly rotate the trimmer motor, while simultaneously controlling the voltage. As soon as we get the voltage within 14.1-14.3 V, we disconnect the charger from the network, fix the trimmer resistor slide with nail polish (at least for nails) and put the case back together. 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 diagram shown, two parallel resistors are used for this (thus obtaining a resistance that is outside the standard range). We also need to solder a trimmer instead and adjust the output to the desired voltage. Here is an example of one of these boards:

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

There are often similar recommendations 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 early 2000s, and such recommendations are not applicable to more or less modern power supplies. In them it is no longer possible to simply raise the 12 V voltage to the required value, since other output voltages are also controlled, and they will inevitably “float away” with such a 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 conversion.

Transformer - converts the mains supply voltage of 220 Volts into the necessary 12 Volts for us, or in some devices up to 14.4 Volts (the latter corresponds to the power supply voltage of the car when the generator is running)

A diode bridge is four diodes connected to each other that convert alternating electricity into direct electricity.

Charge control unit - one of the most important elements that controls charge currents. Allows you to fully charge the battery without overcharging it (does not allow the electrolyte inside the battery to boil)

Regulators, connectors, indicators and other controls.

Wires and terminals to connect to the battery.

So, let's look at one of the cheapest charger samples - the market value is about $40.

Charger Specifications:

Charges batteries from 10 to 75 amp hours.
It is possible to charge 6v or 12v batteries for a car, motorcycle, scooter, moped, etc.
(On the front panel we can visually find a special switch between 6 or 12 Volt battery voltages).
The current supplied to the battery at the end of the charge is reduced automatically.
(On the front panel we can also see an ammeter to indicate the charge current)

Having examined the charger from the inside, we can find the following basic elements
- transformer
- diode bridge
- fuse
- output voltage switch
- wires to the terminals connected to the battery.

In our version there is no charge control unit.

In principle, this scheme also has the right to life and it works as follows.

Operating principle of the charger:

The transformer is designed for a certain charging current - say, no more than 7.5 Amperes.
When connecting a discharged battery with a maximum permissible capacity of 75 Amps, the transformer delivers a maximum permissible current of 7.5 Amps, which is 1/10 of the battery capacity.

As the battery charges, the voltage at its terminals increases and the charging current decreases (which is why, due to the laws of physics, the current supplied to the battery at the end of charging will decrease).

Unfortunately, such a charger is unlikely to finish the charging process, and if your battery is faulty and does not reach the required capacity, the charging current will not decrease.

In the modern world, more and more people are inclined to buy a maintenance-free battery. If something happens to it and it does not charge, it must be replaced.

A charger without a control unit will not help you restore the battery’s properties, but again, rarely does anyone do this these days. More complex devices can create a pulse charging mode, when each charging pulse is followed by a charging pulse. This allows you to restore the properties of the battery.

Often, more advanced chargers also have a discharge function, since the battery must always be in full charge and discharge mode - this allows it to maintain its capacity.

If you use maintenance-free batteries and you simply urgently need to charge the battery after the car has been idle for a long time or after a cold night, you can make such a charger yourself.

1. Transformer.
The first thing you need is a transformer with an output voltage of 12 Volts - 14 Volts with a thick secondary winding that can provide a current equal to 1/10 of the capacity of your battery.

You should not use a transformer for a calculator or player; they are very low-power. Perhaps you will be able to find a more powerful transformer, say from an old TV (such as TS-180-2). If your transformer does not produce the required voltage, you can wind the required secondary yourself - with a thick copper wire several turns until the desired voltage is achieved.

Remember, when you work with a transformer, that it is connected to a 220 Volt network - be very careful (this is life-threatening)!

If you manage to find or make such a transformer, then you will need to buy a diode bridge.

2. Diode bridge

Factory made diode bridge. Designed for high charger currents

This is a fairly common product - all you need to know is the current for which it should be designed. In our case, it is still 7.5 Amperes.
If you couldn’t find a diode bridge, you can find 4 diodes with the same indicator and assemble a diode bridge from them.

Next, at the output of the diode bridge, you need to install a car fuse for the same calculated current of 7.5 Amperes. If you accidentally short the terminals or mix them up on the battery, you will blow the fuse, not the transformer.

3. Ammeter
To complete the picture, you can also install an ammeter in series with the fuse to monitor how much current is flowing from your charger. At the same time, you will be able to understand the current state of the battery.

4. Wires and terminals.
Next come the wires and terminals that can be connected to the battery. Here you have complete freedom of action. It is best to take copper wires with a thickness of at least 1 mm. The terminals can be either regular automotive ones or crocodile clips as on the factory version.

It is also worth placing a fuse in front of the transformer, say 220 Volt 0.5 Ampere, in order to double protect your transformer on both sides, in terms of input and output current.

Thus, you will receive a device that, in several small parameters, will be even better and more reliable than the factory analogue.

If you want to make the device even more functional, you can search the Internet for charge control units.
The main advantages of the battery charge control unit:
- regulates the charge current - reduces it to minimum values ​​until the battery is fully charged
- turns off the charging unit when the battery is fully charged
- discharges the battery completely for a complete clean charging cycle
- charges the battery with pulsed currents, alternating charge and discharge to restore capacity.

In today's hectic world, with unmaintained batteries with a service life of five years, you are unlikely to refurbish batteries.

In any case, good luck to you in your endeavors!

Even with a fully operational car, sooner or later a situation may arise when you need an external source - a long parking period, side lights accidentally left on, and so on. Owners of old equipment are well aware of the need to regularly recharge the battery - this is due to the self-discharge of a “tired” battery and increased leakage currents in electrical circuits, primarily in the diode bridge of the generator.

You can purchase a ready-made charger: they Available in many variants and are easily accessible. But some may think that making a charger for a car battery with their own hands will be more interesting, while for others the ability to make a charger literally from scrap material will help them out.

Semiconductor diode + light bulb

It is not known who first came up with the idea of ​​charging the battery in this way, but this is exactly the case when you can charge the battery literally with improvised means. In this circuit, the current source is a 220V electrical network, a diode is needed to convert alternating current into pulsating direct current, and the light bulb serves as a current-limiting resistor.

The calculation of this charger is as simple as its circuit:

• The current flowing through the lamp is determined based on its power as I=P/U, Where U– network voltage, P– lamp power. That is, for a 60 W lamp, the current in the circuit will be 0.27 A.
• Since the diode cuts off every second half-wave of the sinusoid, the real average load current, taking this into account, will be equal to 0.318*I.