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 charger for a car battery 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 a 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.
Car owners often face a problem battery discharge. If this happens far from service stations, auto shops and gas stations, you can independently make a device for charging the battery from available parts. Let's look at how to make a charger for a car battery with your own hands, having minimal knowledge of electrical installation work.
This device is best used only in critical situations. However, if you are familiar with electrical engineering, electrical and fire safety rules, and have skills in electrical measurements and installation work, a homemade charger can easily replace the factory unit.
Causes and signs of battery discharge
During the operation of the battery, when the engine is running, the battery is constantly recharged from the vehicle's generator. You can check the charging process by connecting a multimeter to the battery terminals with the engine running, measuring the charging voltage of the car battery. The charge is considered normal if the voltage at the terminals is from 13.5 to 14.5 Volts.
To fully charge, you need to drive the car for at least 30 kilometers, or about half an hour in city traffic.
The voltage of a normally charged battery during parking should be at least 12.5 Volts. If the voltage is less than 11.5 Volts, the car engine may not start during the start. Reasons for battery discharge:
- The battery has significant wear ( more than 5 years of operation);
- improper operation of the battery, leading to sulfation of the plates;
- long-term parking of the vehicle, especially in the cold season;
- urban rhythm of car driving with frequent stops when the battery does not have time to charge sufficiently;
- leaving the car's electrical appliances on while parked;
- damage to the electrical wiring and equipment of the vehicle;
- leaks in electrical circuits.
Many car owners do not have the means to measure battery voltage in their on-board tool kit ( voltmeter, multimeter, probe, scanner). In this case, you can be guided by indirect signs of battery discharge:
- dim lights on the dashboard when the ignition is turned on;
- lack of starter rotation when starting the engine;
- loud clicks in the starter area, lights on the dashboard going out when starting;
- complete lack of reaction from the car when the ignition is turned on.
If the listed symptoms appear, first of all you need to check the battery terminals, if necessary, clean and tighten them. In the cold season, you can try to bring the battery into a warm room for a while and warm it up.
You can try to “light” the car from another car. If these methods do not help or are not possible, you have to use a charger.
DIY universal charger. Video:
Operating principle
Most devices charge batteries with constant or pulsed currents. How many amps does it take to charge a car battery? The charge current is chosen equal to one tenth of the battery capacity. With a capacity of 100 Ah, the charging current of a car battery will be 10 Amperes. The battery will have to be charged for about 10 hours until it is fully charged.
Charging a car battery with high currents can lead to the sulfation process. To avoid this, it is better to charge the battery with low currents, but for a longer time.
Pulse devices significantly reduce the effect of sulfation. Some pulse chargers have a desulfation mode, which allows you to restore battery functionality. It consists of sequential charge-discharge with pulsed currents according to a special algorithm.
When charging the battery, do not allow it to overcharge. It can lead to boiling of the electrolyte and sulfation of the plates. It is necessary that the device has its own control system, parameter measurement and emergency shutdown.
Since the 2000s, special types of batteries began to be installed on cars: AGM and gel. Charging a car battery of these types differs from the normal mode.
As a rule, it is three-stage. Up to a certain level, the charge occurs with a large current. Then the current decreases. The final charge occurs with even smaller pulse currents.
Charging a car battery at home
Often in driving practice a situation arises when, having parked the car near the house in the evening, in the morning it is discovered that the battery is discharged. What can be done in such a situation when there is no soldering iron at hand, no parts, but you need to start it?
Usually the battery has a small capacity left; it just needs to be “tightened up” a little so that there is enough charge to start the engine. In this case, a power supply from some household or office equipment, for example, a laptop, can help.
Charging from a laptop power supply
The voltage produced by the laptop power supply is usually 19 Volts, the current is up to 10 Amps. This is enough to charge the battery. But you CANNOT connect the power supply directly to the battery. It is necessary to include a limiting resistance in series in the charging circuit. You can use a car light bulb as it, better for interior lighting. It can be purchased at your nearest gas station.
Typically the middle pin of the connector is positive. A light bulb is connected to it. The + battery is connected to the second terminal of the light bulb.
The negative terminal is connected to the negative terminal of the power supply. The power supply usually has a label indicating the polarity of the connector. A couple of hours of charging using this method is enough to start the engine.
Scheme of a simple charger for a car battery.
Charge from a household network
A more extreme charging method is directly from a household outlet. It is used only in a critical situation, using maximum electrical safety measures. To do this you will need a lighting lamp ( not energy saving).
You can use an electric stove instead. You also need to purchase a rectifier diode. Such a diode can be “borrowed” from a faulty energy-saving lamp. During this time, it is better to turn off the voltage supplied to the apartment. The diagram is shown in the figure.
The charging current with a lamp power of 100 Watts will be approximately 0.5 A. Overnight the battery will be recharged for only a few ampere-hours, but this may be enough to start. If you connect three lamps in parallel, the battery will be charged three times more. If you connect an electric stove instead of a light bulb ( at the lowest power), then the charging time will be significantly reduced, but this is very dangerous. In addition, the diode may break through, then the battery may short out. Charging methods from 220 V are dangerous.
DIY car battery charger. Video:
Homemade car battery charger
Before making a charger for a car battery, you should evaluate your experience in electrical installation work and knowledge of electrical engineering, and based on this, proceed to choosing a charger circuit for a car battery.
You can look in the garage to see if there are old devices or units. A power supply from an old computer is suitable for the device. It has almost everything:
- 220 V connector;
- power switch;
- electrical circuit;
- cooling Fan;
- connection terminals.
The voltages on it are standard: +5 V, -12 V and +12 Volts. To charge the battery, it is better to use a +12 Volt, 2 Ampere wire. The output voltage must be raised to the level of +14.5 - +15.0 Volts. This can usually be done by changing the resistance value in the feedback circuit ( about 1 kiloohm).
There is no need to install a limiting resistance; the electronic circuit will independently regulate the charge current within 2 Amperes. It is easy to calculate that it will take about a day to fully charge a 50 A*h battery. Appearance of the device.
You can pick up or buy at a flea market a network transformer with a secondary winding voltage of 15 to 30 Volts. These were used in old TVs.
Transformer devices
The simplest circuit diagram of a device with a transformer.
Its disadvantage is the need to limit the current in the output circuit and the associated large power losses and heating of the resistors. Therefore, capacitors are used to regulate the current.
Theoretically, having calculated the value of the capacitor, you can not use a power transformer, as shown in the diagram.
When purchasing capacitors, you should choose the appropriate rating with a voltage of 400 V or more.
In practice, devices with current regulation have become more widely used.
You can choose pulse homemade charger circuits for a car battery. They are more complex in circuit design and require certain installation skills. Therefore, if you do not have special skills, it is better to buy a factory unit.
Pulse chargers
Pulse chargers have a number of advantages:
The operating principle of pulse devices is based on converting alternating voltage from a household electrical network into direct voltage using a VD8 diode assembly. The DC voltage is then converted into pulses of high frequency and amplitude. Pulse transformer T1 again converts the signal into DC voltage, which charges the battery.
Since the reverse conversion is carried out at a high frequency, the dimensions of the transformer are much smaller. The feedback necessary to control the charge parameters is provided by optocoupler U1.
Despite the apparent complexity of the device, when assembled correctly the unit begins to work without additional adjustment. This device provides a charging current of up to 10 Amps.
When charging the battery using a homemade device, you must:
- place the device and battery on a non-conductive surface;
- comply with electrical safety requirements ( use gloves, a rubber mat, and tools with an electrical insulating coating);
- Do not leave the charger turned on for a long time without control, monitor the voltage and temperature of the battery, and the charging current.
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A fairly simple automatic charger can be implemented on the LM317 chip, which is a linear voltage regulator with an adjustable output voltage. The microcircuit can also work as a current stabilizer.
A high-quality charger for a car battery can be purchased on the market for $50, and today I will tell you the easiest way to make such a charger with minimal expenditure of money; it is simple and even a novice radio amateur can make it.
The design of a simple charger for car batteries can be implemented in half an hour at minimal cost; the process of assembling such a charger will be described below.
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Recently, I came across a diagram of a powerful charger for car batteries with a current of up to 20A on the Internet. In fact, this is a powerful regulated power supply assembled with just two transistors. The main advantage of the circuit is the minimum number of components used, but the components themselves are quite expensive, we are talking about transistors.
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Recently I came up with the idea of assembling a car charger based on cheap Chinese power supplies with a price of $5-10. In electronics stores you can now find units that are designed to power LED strips. Since such tapes are powered by 12 Volts, therefore the output voltage of the power supply is also within 12 Volts
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After the article charger from an electronic transformer, many letters were sent to my email address asking me to explain and tell how to power up the circuit of an electronic transformer, and in order not to write to each user separately, I decided to print this article, where I will talk about the main components that need will be modified to increase the output power of the electronic transformer.
The vehicle's on-board network is powered by the battery until the power plant starts. But it itself does not generate electrical energy. The battery is simply a container for electricity, which is stored in it and, if necessary, given to consumers. Afterwards, the expended energy is restored due to the operation of the generator, which produces it.
But even constant recharging of the battery from a generator is not able to completely restore the expended energy. This requires periodic charging from an external source rather than a generator.
Design and principle of operation of the charger
Chargers are used to produce. These devices operate from a 220 V network. In fact, the charger is a conventional electrical energy converter.
It takes the alternating current of the 220 V network, lowers it and converts it into direct current with a voltage of up to 14 V, that is, to the voltage that the battery itself produces.
Nowadays a large number of all kinds of chargers are produced - from primitive and simple ones to devices with a large number of various additional functions.
Chargers are also sold, which, in addition to possibly recharging the battery installed on the car, can also start the power plant. Such devices are called charging and starting devices.
There are also autonomous charging and starting devices that can recharge the battery or start the engine without connecting the device itself to a 220 V network. Inside such a device, in addition to equipment that converts electrical energy, there is also one, which makes such a device autonomous, although the battery of the device is also After each release of electricity, charging is required.
Video: How to make a simple charger
As for conventional chargers, the simplest of them consists of only a few elements. The main element of such a device is a step-down transformer. It lowers the voltage from 220 V to 13.8 V, which is the most optimal for charging the battery. However, the transformer only lowers the voltage, but converting it from alternating current to direct current is performed by another element of the device - a diode bridge, which rectifies the current and divides it into positive and negative poles.
Behind the diode bridge, an ammeter is usually included in the circuit, which shows the current strength. The simplest device uses a dial ammeter. In more expensive devices, it can be digital; in addition to the ammeter, a voltmeter can also be built-in. Some chargers have the ability to select voltage; for example, they can charge both 12-volt and 6-volt batteries.
Wires with “positive” and “negative” terminals come out of the diode bridge, which connect the device to the battery.
All this is enclosed in a housing, from which comes a wire with a plug for connecting to the network, and wires with terminals. To protect the entire circuit from possible damage, a fuse is included in it.
In general, this is the entire circuit of a simple charger. Charging the battery is relatively simple. The terminals of the device are connected to the discharged battery, but it is important not to mix up the poles. The device is then connected to the network.
At the very beginning of charging, the device will supply voltage with a current of 6-8 amperes, but as charging progresses, the current will decrease. All this will be displayed on the ammeter. If the battery is fully charged, the ammeter needle will drop to zero. This is the entire process of charging the battery.
The simplicity of the charger circuit makes it possible to manufacture it yourself.
Making your own car charger
Now let's look at the simplest chargers that you can make yourself. The first will be a device that is very similar in concept to the one described.
The diagram shows:
S1 - power switch (toggle switch);
FU1 - 1A fuse;
T1 - transformer TN44;
D1-D4 - diodes D242;
C1 - capacitor 4000 uF, 25 V;
A - 10A ammeter.
So, to make a homemade charger you will need a step-down transformer TS-180-2. Such transformers were used on old tube TVs. Its feature is the presence of two primary and secondary windings. Moreover, each of the secondary output windings has 6.4 V and 4.7 A. Therefore, in order to achieve the 12.8 V required for charging the battery, which this transformer is capable of, you need to connect these windings in series. For this, a short wire with a cross-section of at least 2.5 mm is used. sq. The jumper connects not only the secondary windings, but also the primary ones.
Video: The simplest battery charger
Next, you will need a diode bridge. To create it, 4 diodes are taken, designed for a current of at least 10 A. These diodes can be fixed on a textolite plate, and then they can be connected correctly. Wires are connected to the output diodes, which the device will connect to the battery. At this point, the assembly of the device can be considered complete.
Now about the correctness of the charging process. When connecting a device to a battery, do not reverse the polarity, otherwise you can damage both the battery and the device.
When connecting to a battery, the device must be completely de-energized. You can turn it on only after connecting it to the battery. It should also be disconnected from the battery after disconnecting from the network.
A heavily discharged battery cannot be connected to the device without a means that reduces the voltage and current, otherwise the device will supply a high current to the battery, which can damage the battery. An ordinary 12-volt lamp, which is connected to the output terminals in front of the battery, can act as a reducing agent. The lamp will light up when the device is operating, thereby partially absorbing the voltage and current. Over time, after the battery is partially charged, the lamp can be removed from the circuit.
When charging, you need to periodically check the state of charge of the battery, for which you can use a multimeter, voltmeter or load plug.
A fully charged battery, when checking its voltage, should show at least 12.8 V; if the value is lower, further charging is required to bring this indicator to the desired level.
Video: DIY car battery charger
Since this circuit does not have a protective housing, you should not leave the device unattended during operation.
And even if this device does not provide the optimal 13.8 V output, it is quite suitable for recharging the battery, although after about two years of using the battery, you will still need to charge it with a factory device that provides all the optimal parameters for charging the battery.
Transformerless charger
An interesting design is the circuit of a homemade device that does not have a transformer. Its role in this device is played by a set of capacitors designed for a voltage of 250 V. There must be at least 4 such capacitors. The capacitors themselves are connected in parallel.
A resistor is connected in parallel to the set of capacitors, designed to suppress the residual voltage after disconnecting the device from the network.
Next, you will need a diode bridge to operate with a permissible current of at least 6 A. It is connected to the circuit after a set of capacitors. And then the wires that will connect the device to the battery are connected to it.