Let's consider the operation of the circuit (Fig. 1) in the first mode. An alternating voltage of 220 V is supplied to the step-down transformer Tr1. In the secondary winding, two voltages of 24 V are generated relative to the midpoint. We managed to find a transformer with a midpoint in the secondary winding, which makes it possible to reduce the number of diodes in the rectifiers, create a power reserve and ease the thermal regime. The alternating voltage from the secondary winding of the transformer is supplied to a rectifier using diodes D6, D7. The plus from the middle point of the transformer goes to resistor R8, which limits the current of the zener diode D1. Zener diode D1 determines the operating voltage of the circuit. A thyristor control generator is assembled on transistors T1 and T2. Capacitor C1 is infected through the circuit: power supply plus, variable resistor R3, R1, C1, minus. The charging rate of capacitor C1 is controlled by variable resistor R3. Capacitor C1 is discharged along the circuit: emitter - collector T1, base - emitter T2, R4 capacitor mine. Transistors T1 and T2 open and a positive pulse from the emitter T2 through the limiting resistor R7 and decoupling diodes D4 - D5 arrives at the control electrodes of the thyristors. In this case, switch Vk 1 is turned on, Vk 2 is turned off. The thyristors, depending on the minus phase of the alternating voltage, open one by one, and the minus of each half-cycle goes to the minus of the battery. Plus from the midpoint of the transformer through the ammeter to the plus of the battery. Resistors R5 and R6 determine the operating mode of transistors T1-2. R4 is the load of the T2 emitter on which a positive control pulse is released. R2 - for more stable operation of the circuit (in some cases it can be neglected).
Operation of the memory circuit in the second mode (Vk1 – off; Vk2 – on). When Vk1 is turned off, the control circuit of thyristor D3 is interrupted, while it remains permanently closed. One thyristor D2 remains in operation, which rectifies only one half-cycle and produces a charge pulse during one half-cycle. During the idle second half-cycle, the battery is discharged through the switched on Vk2. The load is an incandescent light bulb 24V x 24 W or 26V x 24 W (when the voltage on it is 12V, it consumes a current of 0.5 A). The light bulb is placed outside the housing so as not to heat the structure. The charging current value is set by regulator R3 using an ammeter. Considering that when charging the battery, part of the current flows through load L1 (10%). Then the ammeter reading should correspond to 1.8A (for a pulse charging current of 5A). since the ammeter has an inertia and shows the average value of the current over a period of time, and the charge is made during half the period.
Details and design of the charger. Any transformer with a power of at least 150 W and a voltage in the secondary winding of 22 - 25 V is suitable. If you use a transformer without a midpoint in the secondary winding, then all elements of the second half-cycle must be excluded from the circuit. (Bk1, D5, D3). The circuit will be fully operational in both modes, only in the first it will work on one half-cycle. Thyristors can be used KU202 for a voltage of at least 60V. They can be installed on a radiator without isolation from each other. Any D4-7 diodes for an operating voltage of at least 60V. Transistors can be replaced with germanium low-frequency transistors with appropriate conductivity. works on any pairs of transistors: P40 – P9; MP39 – MP38; KT814 – KT815, etc. Zener diode D1 is any 12–14V. You can connect two in series to set the desired voltage. As an ammeter, I used the head of a 10 mA, 10 division miliammeter. The shunt was selected experimentally, wound with 1.2 mm wire without a frame to a diameter of 8 mm, 36 turns.
Setting up the charger. If assembled correctly, it works immediately. Sometimes it is necessary to set the Min - Max regulation limits. selection of C1, usually in the direction of increase. If there are regulation failures, select R3. Usually I connected a powerful light bulb from an overhead projector 24V x 300W as a load for adjustment. It is advisable to install a 10A fuse in the open circuit of the battery charge.
Discuss the article BATTERY CHARGER
In order for a car to start, it needs energy. This energy is taken from the battery. As a rule, it is recharged from the generator while the engine is running. When the car is not used for a long time or the battery is faulty, it discharges to such a state that that the car can no longer start. In this case, external charging is required. You can buy such a device or assemble it yourself, but for this you will need a charger circuit.
The principle of operation of a car battery
A car battery supplies power to various devices in the car when the engine is turned off and is designed to start it. By type of execution, a lead-acid battery is used. Structurally, it is assembled from six batteries with a nominal voltage of 2.2 volts, connected in series. Each element is a set of lattice plates made of lead. The plates are coated with active material and immersed in an electrolyte.
The electrolyte solution contains distilled water and sulfuric acid. The frost resistance of the battery depends on the density of the electrolyte. Recently, technologies have emerged that allow the electrolyte to be adsorbed in glass fiber or thickened using silica gel to a gel-like state.
Each plate has a negative and positive pole, and they are isolated from each other using a plastic separator. The body of the product is made of propylene, which is not destroyed by acid and serves as a dielectric. The positive pole of the electrode is coated with lead dioxide, and the negative with sponge lead. Recently, rechargeable batteries with electrodes made of lead-calcium alloy have begun to be produced. These batteries are completely sealed and require no maintenance.
When a load is connected to the battery, the active material on the plates reacts chemically with the electrolyte solution and produces an electric current. The electrolyte depletes over time due to the deposition of lead sulfate on the plates. The battery begins to lose charge. During the charging process, a chemical reaction occurs in the reverse order, lead sulfate and water are converted, the density of the electrolyte increases and the charge is restored.
Batteries are characterized by their self-discharge value. It occurs in the battery when it is inactive. The main reason is contamination of the battery surface and poor quality of the distiller. The rate of self-discharge accelerates when the lead plates are destroyed.
Types of chargers
A large number of car charger circuits have been developed using different element bases and fundamental approaches. According to the principle of operation, charging devices are divided into two groups:
- Starting chargers, designed to start the engine when the battery is not working. By briefly supplying a large current to the battery terminals, the starter is turned on and the engine starts, and then the battery is charged from the car's generator. They are produced only for a certain current value or with the ability to set its value.
- Pre-start chargers, leads from the device are connected to the battery terminals and current is supplied for a long time. Its value does not exceed ten amperes, during which time the battery energy is restored. In turn, they are divided into: gradual (charging time from 14 to 24 hours), accelerated (up to three hours) and conditioning (about an hour).
Based on their circuit design, pulse and transformer devices are distinguished. The first type uses a high-frequency signal converter and is characterized by small size and weight. The second type uses a transformer with a rectifier unit as a basis; it is easy to manufacture, but have a lot of weight and low efficiency (efficiency).
Whether you made a charger for car batteries yourself or purchased it at a retail outlet, the requirements for it are the same, namely:
- output voltage stability;
- high efficiency value;
- short circuit protection;
- charge control indicator.
One of the main characteristics of the charger is the amount of current that charges the battery. Correctly charging the battery and extending its performance characteristics can only be achieved by selecting the desired value. The charging speed is also important. The higher the current, the higher the speed, but a high speed value leads to rapid degradation of the battery. It is believed that the correct current value will be a value equal to ten percent of the battery capacity. Capacity is defined as the amount of current supplied by the battery per unit of time; it is measured in ampere-hours.
Homemade charger
Every car enthusiast should have a charging device, so if there is no opportunity or desire to purchase a ready-made device, there is nothing left to do but charge the battery yourself. It is easy to make with your own hands both the simplest and multifunctional devices. For this you will need a diagram and a set of radioelements. It is also possible to convert an uninterruptible power supply (UPS) or computer unit (AT) into a device for recharging the battery.
Transformer charger
This device is the easiest to assemble and does not contain scarce parts. The circuit consists of three nodes:
- transformer;
- rectifier block;
- regulator
Voltage from the industrial network is supplied to the primary winding of the transformer. The transformer itself can be used of any type. It consists of two parts: the core and the windings. The core is assembled from steel or ferrite, the windings are made from conductor material.
The operating principle of the transformer is based on the appearance of an alternating magnetic field when current passes through the primary winding and transfers it to the secondary. To obtain the required voltage level at the output, the number of turns in the secondary winding is made smaller compared to the primary. The voltage level on the secondary winding of the transformer is selected to be 19 volts, and its power should provide a threefold reserve of charging current.
From the transformer, the reduced voltage passes through the rectifier bridge and goes to a rheostat connected in series to the battery. The rheostat is designed to regulate the voltage and current by changing the resistance. The rheostat resistance does not exceed 10 Ohms. The amount of current is controlled by an ammeter connected in series in front of the battery. With this circuit it will not be possible to charge a battery with a capacity of more than 50 Ah, since the rheostat begins to overheat.
You can simplify the circuit by removing the rheostat, and install a set of capacitors at the input in front of the transformer, which are used as reactance to reduce the network voltage. The lower the nominal value of the capacitance, the less voltage is supplied to the primary winding in the network.
The peculiarity of such a circuit is that it is necessary to ensure a signal level on the secondary winding of the transformer that is one and a half times greater than the operating voltage of the load. This circuit can be used without a transformer, but it is very dangerous. Without galvanic isolation, you can get an electric shock.
Pulse charger
The advantage of pulsed devices is their high efficiency and compact size. The device is based on a pulse-width modulation (PWM) chip. You can assemble a powerful pulse charger with your own hands according to the following scheme.
The IR2153 driver is used as a PWM controller. After the rectifier diodes, a polar capacitor C1 with a capacity in the range of 47–470 μF and a voltage of at least 350 volts is placed in parallel with the battery. The capacitor removes mains voltage surges and line noise. The diode bridge is used with a rated current of more than four amperes and with a reverse voltage of at least 400 volts. The driver controls powerful N-channel field-effect transistors IRFI840GLC installed on radiators. The current of such charging will be up to 50 amperes, and the output power will be up to 600 watts.
You can make a pulse charger for a car with your own hands using a converted AT format computer power supply. They use the common TL494 microcircuit as a PWM controller. The modification itself consists of increasing the output signal to 14 volts. To do this, you will need to correctly install the trimmer resistor.
The resistor that connects the first leg of the TL494 to the stabilized + 5 V bus is removed, and instead of the second one, connected to the 12 volt bus, a variable resistor with a nominal value of 68 kOhm is soldered in. This resistor sets the required output voltage level. The power supply is turned on via a mechanical switch, according to the diagram indicated on the power supply housing.
Device on LM317 chip
A fairly simple but stable charging circuit is easily implemented on the LM317 integrated circuit. The microcircuit provides a signal level of 13.6 volts with a maximum current of 3 amperes. The LM317 stabilizer is equipped with built-in short circuit protection.
Voltage is supplied to the device circuit through the terminals from an independent DC power supply of 13-20 volts. The current, passing through the indicator LED HL1 and transistor VT1, is supplied to the stabilizer LM317. From its output directly to the battery via X3, X4. The divider assembled on R3 and R4 sets the required voltage value for opening VT1. Variable resistor R4 sets the charging current limit, and R5 sets the output signal level. The output voltage is adjustable from 13.6 to 14 volts.
The circuit can be simplified as much as possible, but its reliability will decrease.
In it, resistor R2 selects the current. A powerful nichrome wire element is used as a resistor. When the battery is discharged, the charging current is maximum, the VD2 LED lights up brightly; as the battery charges, the current begins to decrease and the LED dims.
Charger from an uninterruptible power supply
The rectifier is assembled using any powerful diodes, for example, domestic D-242 and a network capacitor of 2200 uF for 35-50 volts. The output will be a signal with a voltage of 18-19 volts. An LT1083 or LM317 microcircuit is used as a voltage stabilizer and must be installed on a radiator.
By connecting the battery, the voltage is set to 14.2 volts. It is convenient to control the signal level using a voltmeter and ammeter. The voltmeter is connected in parallel to the battery terminals, and the ammeter in series. As the battery charges, its resistance will increase and the current will decrease. It’s even easier to make the regulator using a triac connected to the primary winding of the transformer like a dimmer.
When making a device yourself, you should remember about electrical safety when working with a 220 V AC network. As a rule, a correctly made charging device made from serviceable parts starts working immediately, you just need to set the charging current.
The device with electronic control of the charging current is made on the basis of a thyristor phase-pulse power regulator. It does not contain scarce parts, and if the elements are known to be good, it does not require adjustment.
The charger allows you to charge car batteries with a current from 0 to 10 A, and can also serve as a regulated power source for a powerful low-voltage soldering iron, vulcanizer, or portable lamp. The charging current is similar in shape to pulse current, which is believed to help extend battery life. The device is operational at ambient temperatures from - 35 °C to + 35 °C.
The device diagram is shown in Fig. 2.60.
The charger is a thyristor power regulator with phase-pulse control, powered from winding II of the step-down transformer T1 through the moctVDI + VD4 diode.
The thyristor control unit is made on an analogue of the unijunction transistor VT1, VT2. The time during which capacitor C2 is charged before switching the unijunction transistor can be adjusted with a variable resistor R1. When the engine is in the extreme right position according to the diagram, the charging current will be maximum, and vice versa.
Diode VD5 protects the control circuit of thyristor VS1 from reverse voltage that occurs when the thyristor is turned on.
The charger can later be supplemented with various automatic components (switching off at the end of charging, maintaining normal battery voltage during long-term storage, signaling the correct polarity of the battery connection, protection against output short circuits, etc.).
The disadvantages of the device include fluctuations in the charging current when the voltage of the electric lighting network is unstable.
Like all similar thyristor phase-pulse regulators, the device interferes with radio reception. To combat them, you should provide an LC network filter, similar to that used in switching network power supplies.
Capacitor C2 - K73-11, with a capacity of 0.47 to 1 µF, or. K73-16, K73-17, K42U-2, MBGP.
We will replace the KT361A transistor with KT361B - KT361Ё, KT3107L, KT502V, KT502G, KT501Zh - KT50IK, and KT315L with KT315B + KT315D KT312B, KT3102L, KT503V + KT503G, P307 Instead 05B suitable diodes KD105V, KD105G or. D226 with any letter index.
Variable resistor R1 - SP-1, SPZ-30a or SPO-1.
Ammeter PA1 - any direct current with a scale of 10 A. It can be made independently from any milliammeter by selecting a shunt based on a standard ammeter.
Fuse F1 is a fuse, but it is convenient to use a 10 A circuit breaker or a car bimetallic fuse for the same current.
Diodes VD1 + VP4 can be any for a forward current of 10 A and a reverse voltage of at least 50 V (series D242, D243, D245, KD203, KD210, KD213).
The rectifier diodes and thyristor are installed on heat sinks, each with a useful area of about 100 cm2. To improve the thermal contact of devices with heat sinks, it is advisable to use thermally conductive pastes.
Instead of a thyristor. KU202V will fit KU202G - KU202E; It has been verified in practice that the device works normally with more powerful thyristors T-160, T-250.
It should be noted that it is permissible to use the metal casing wall directly as a heat sink for the thyristor. Then, however, there will be a negative terminal of the device on the case, which is generally undesirable due to the danger of accidental short circuits of the positive output wire to the case. If you mount the thyristor through a mica gasket, there will be no danger of a short circuit, but the heat transfer from it will worsen.
The device can use a ready-made network step-down transformer of the required power with a secondary winding voltage of 18 to 22 V.
If the transformer has a voltage on the secondary winding of more than 18 V, resistor R5 should be replaced with another one of higher resistance (for example, at 24...26 V, the resistor resistance should be increased to 200 Ohms).
In the case when the secondary winding of the transformer is tapped from the middle, or there are two identical windings and the voltage of each is within the specified limits, then it is better to make the rectifier according to a standard full-wave circuit using two diodes.
When the secondary winding voltage is 28...36 V, you can completely abandon the rectifier - its role will simultaneously be played by thyristor VS1 (rectification is half-wave). For this version of the power supply, it is necessary to connect a separating diode KD105B or D226 with any letter index (cathode to resistor R5) between resistor R5 and the positive wire. The choice of thyristor in such a circuit will be limited - only those that allow operation under reverse voltage (for example, KU202E) are suitable.
For the described device, a unified transformer TN-61 is suitable. Its three secondary windings must be connected in series, and they are capable of delivering current up to 8 A.
All parts of the device, except for transformer T1, rectifier diodes VD1 - VD4, variable resistor R1, fuse FU1 and thyristor VS1, are mounted on a printed circuit board made of foil fiberglass 1.5 mm thick.
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