Automatic charger and starter for a car battery. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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Starting devices of industrial production often have low power and are not sufficiently reliable in operation. The simplest self-made circuits of automotive starting devices, consisting only of a transformer and power rectifier diodes, also have a number of disadvantages.

First, if the output wires are accidentally shorted, expensive rectifier diodes can easily be damaged. If the polarity of connecting such a circuit to the battery is incorrect, the on-board electronics or the battery itself can be damaged. In addition, in the manufacture of the simplest starting device, it is required to correctly select the parameters of the transformer (the ratio of the number of turns of the primary and secondary windings for a particular type of magnetic circuit), so that it provides a current to the load of at least 100 A with a voltage drop of at least 10 V.

To eliminate all these shortcomings allows the device described below. It can also be used to recharge or train the battery, and the automation will not allow the battery voltage to exceed the permissible value in all operating modes.

The electrical circuit provides stabilization of the output voltage and current protection against short circuits. And if the battery is connected to the output terminals of the device with the wrong polarity, it will not allow it to be turned on.

To operate the starter-charger in different modes, the battery is connected to the same output terminals, which is very convenient during operation. At the same time, the operation of the circuit and the state of the battery are monitored using a voltmeter and an ammeter installed on the front panel of the case, fig. 4.13. The regulators located in the same place can change the output voltage U and the limiting (protection) current I over a wide range.

Rice. 4.13 Front panel view

The device can operate in three modes, which are selected by switch SA1 ("mode"):

1. Charging - the rechargeable battery (AB) is charged with a stable current until the voltage on the battery rises to 14,8 V. In this case, the charging current can be set to any in the range of 1 ... 10 A.

2. Training - is used to prevent sulfation of the battery plates during its long-term storage with electrolyte supplied, for example, in winter. The device allows you to cycle through the charge-discharge process in automatic mode. The charge current can be set from 1 A, discharge - 10 A. The number of cycles is not limited.

3. Start-mode is used to start the car engine. In this case, the device is connected in parallel with the battery and provides a current of up to 100 A in continuous mode. This makes it easier to start the engine in winter or with reduced battery capacity due to aging.

The electrical circuit of the charger-starter, fig. 4.14, consists of the following parts:

a) power transformer T1 with a power of about 1 kW with a rectifier made on thyristors VS1, VS2;

b) power supply for the control circuit on the transformer T2 and stabilizers DA2, DA3;

c) automatic control schemes (DA1.DA4, TK);

d) mode control circuits (PV1, amplifier DA6 for measuring current, PA1.HL1, HL2);

e) switching and protection unit (K1, K2, DA5).

Rice. 4.14. The electrical circuit of the charger-starter

Table 4.1. The supply voltage on the microcircuits

Since it is recommended to maintain the average charging current constant when charging a car battery, thyristors are used as a regulating element. They simultaneously work as controlled rectifiers.

For ease of manufacture, the control circuit is powered by a separate transformer T2. A signal is also removed from it to synchronize the operation of the circuit with the mains frequency (a circuit of VD6-R28-R33 elements). The +15 V and -15 V voltages used to power the control circuit are stabilized on the DA2 and DA3 microcircuits.

The automatic control unit works as follows. The voltage feedback signal (Uoc) from the output terminals (X1, X2) through the resistors R1-R4 is fed to the input of the DA1.1 integrator. The output amplified voltage is added to the voltage set by the resistor R14 and is fed to the input DA4.15.

Chip DA4 (KR1114EU4) is designed specifically for building pulse control circuits, which greatly simplifies the device. It contains a complete set of functional units for performing pulse-width control (Fig. 4.15) and inside it has: a precision reference voltage source +5 V (ION); error amplifiers (1 and 2), comparators (3 and 4), control circuits for the output stage on transistors and a sawtooth voltage generator. The generator frequency is set by an external resistor R30 and capacitor C15. The operation of the oscillator is synchronized with the mains frequency using the transistor VT1, the opening signal of which comes from the rectifier VD6.

Rice. 4.15. Structural diagram of the KR1114EU microcircuit

At the output of the DA4 / 8 microcircuit, a voltage pulse is formed, the width of which depends on the position of the regulators R19, R14. Since short pulses are sufficient to open the thyristors, a differentiating circuit C18-R45 is used to obtain them. These pulses are amplified by transistors VT2, VT3 and through a galvanically decoupling pulse transformer (T3) are fed to the control outputs of the thyristors (VS1, VS2).

The current stabilization function is performed as follows. The current feedback signal (loc), taken from the shunt Ruj, is fed through the resistor R5 to the input of the integrator DA1/7. The integrator amplifies the voltage by 10 times, and also smoothes out the ripples. The signal from the output DA1 / 10 is mixed with the voltage set by the resistor R14. The difference between these voltages is fed to the input (DA4 / 2) of the current-limiting amplifier. Inside the microcircuit, the signals coming to the inputs DA4 / 4 and DA4 / 2 are compared, and the larger of them directly affects the width of the control pulses and, as a result, at the moment of opening the thyristors.

The operation of the circuit is controlled by the PV1 voltmeter and PA1 ammeter.

When the device is used as a starting device, the PA1 ammeter is connected directly to the shunt by the SA1 switch. At a current of 100 A, the voltage on the shunt should be 75 mV and it is quite enough to deflect the instrument needle to full scale. In the case when the operating current is needed up to 10 A (“charging” or “training” mode), an amplifier (DA6) with a factor of 10 is installed for its more accurate measurement, and the PA1 ammeter needle can also deviate to full scale.

The indication of the device operation mode is carried out by LEDs: the HL1 LED glows - work, HL2 - the device is turned off and the battery is being discharged with a current of 0,8 A (in training mode).

The power-on and protection unit starts working when the battery is connected to terminals X1, X2 in the correct polarity. In this case, if the machine is turned on. A1, when the SB1 button is pressed, due to the current flowing from the battery through the K1 winding, the R67 resistor and the VD22 diode, the K1 relay will turn on and with its contacts (K1.1, K1.2) will supply power to the T1 transformer and the control circuit, and will also block button chain (K1,3). It is easy to see that if the polarity of the battery is connected incorrectly, the VD22 diode will be closed and will not allow relay K1 to turn on.

A voltage comparator is assembled on the DA5 chip, which, depending on the mode selected by the SA1 switch, controls the device operation algorithm, preventing the battery voltage from exceeding the predetermined (by resistor R41) level of 14,8 V. This effective value - the amplitude will be greater. The circuit from R48-VD17 provides the hysteresis of the comparator.

Let us now consider in more detail the features of the operation of the charger-starter in different modes.

Charging mode

The required charge current in the current stabilization mode is set by resistor R14 when the voltage regulator R19 is set to maximum. The charging current is controlled by the PA1 ammeter.

To carry out the charge, the battery is connected to the terminals "+" (X1) and "-" (X2) of the device, observing the polarity. When you press the SB1 button, the circuit will start working. As soon as the output voltage, set by the resistor R19, exceeds the level available on the battery, current begins to flow from the transformer (T1) through the shunt (Rsh) in its charge circuit, creating a voltage on it. This voltage enters the input of the current feedback integrator DA1.1. It will change until it compensates for the reference voltage set at the DA4/2 input (this voltage, in turn, determines the moment when the thyristors open, and hence the current in the power circuit).

Thus, the stabilization of current or voltage in this and other modes of operation of the device is the process of setting such a moment of opening of the thyristors, at which the voltage at the output of the device through the feedback circuit compensates for the reference voltage at a certain point.

If the circuit operates in current stabilization mode, then as the battery charges, the voltage on it will increase. As soon as it reaches the level of 14,8 V, the DA5 comparator is triggered and the signal coming from its output to the DA4 / 4 input stops the formation of the pulses that control the opening of the thyristors.

Training mode

The training process is basically similar to the charging process, except that when the SA1 switch is set to the appropriate mode, the DA5 comparator monitors the voltage level on the battery and, if it exceeds 14,8 V, sends a lock signal to the DA4 / 4 input. Which leads to the disappearance of the pulses (DA4 / 8) that control the opening of the thyristors. In this case, the transistor VT5 will also open and the relay K3 will work. It will connect the load (R3.1) with its contacts K68 to discharge the battery. Resistor R68 provides a discharge current of 0,8 A.

The discharge will occur until the voltage on the battery drops to 10,5 V. As soon as this happens, the zero level will appear at the output of the DA5 comparator again, which will turn off the relay. Short circuit and the circuit will go into battery charging mode. This charge-discharge process will be repeated periodically, and the number of cycles is not limited.

Start mode

In this mode, not only the output current of the device is limited in order to protect it from damage, but also the output voltage level to a safe value for the battery and the on-board network.

To work in this mode, the current regulator R14 is set to the maximum, and the resistor R19 sets the voltage of 1 ... 13 V according to the PV14 device.

Now you can insert the key into the car ignition and start the engine. In this case, depending on the starting conditions, the arrow PA1 may occupy different positions on the scale, and its maximum value will correspond to 100 A. The arrow of the PV1 voltmeter may deviate downward.

Assembly features and design

The body of the device has dimensions of 340x240x200 mm and is made of sheet duralumin. Thyristors VS1 and VS2 are mounted on radiators with an area of ​​about 1000 cmXNUMX. (standard heatsinks for these thyristors have just such a surface area).

Structurally, the part of the parts highlighted in the diagram by a dotted line, except for the SA1 switch, is located on a double-sided printed circuit board made of fiberglass with a thickness of 2,5.3,5 mm and a size of 145x110. MM, fig. 4.17.4.19.

Elements VD5 and R8, R9 are installed under T2, C5, C6, respectively, to increase the mounting density. The tuned resistors are fixed on the board one above the other, as shown in Fig. 4.20.

To prevent the circuit of printed conductors during installation, under the transformer. T3 and tuned resistors are placed under a dielectric gasket. In addition, it is necessary to make two volumetric jumpers on the board between the outputs DA5 / 2-DA4 / 7-VT1 / e.

Rice. 4.17. PCB layout from mounting side

Rice. 4.18. Topology of the printed circuit board from the side of the installation of parts

Rice. 4.19. The location of the elements on the board (the DA6 chip is shown without a heatsink)

Rice. 4.20. Installation of trimmers on the board

The connection of the printed circuit board with the rest of the parts is made through the connector. HZ type. РШ2Н-2-15 and contact petals from any miniature connector. Connecting wires to regulators R14 and R19 must be shielded.

The installation of the power section (from transformer T1 to thyristors and terminals X1, X2) is carried out with a flexible stranded wire with a cross section of at least 8 mmXNUMX, for example, a brand. PVZ.

In the device, microcircuits can be replaced by imported analogues DA1 - A747C; DA2-TL494L; DA3-78L15; DA4-79L15; DA5-LM211N; DA6 - no analogues.

Diodes of the KD521 type installed at the inputs of the microcircuits prevent their accidental damage during the circuit setup and can be replaced by any low-power pulse diodes: KD522, KD510, KD503, etc.

Adjustable resistors (R38, R40, R41, R44) for ease of adjustment used multi-turn type SP5-3, adjusting R14, R19 type SPZ-4a-0,25 W with a linear characteristic (A) of resistance change, the rest can be of any type, for example MLT - the corresponding power.

polar capacitors. C10, C11, C13, C14 and C17 type K50-35; C3, C4 type K42U-2 at 0,015 uF at 630 V; the rest from the K10 series or. KM-6.

As measuring instruments, a pointer voltmeter PV1 and an ammeter RA1 of the same type M42301 were used. Since the ammeter has an internal shunt, you will need to open the case and remove it. Indeed, in the circuit for measuring a current of 100 A, an external shunt (Ruj) is used. The shunt Rm was taken as a standard type 75ShSM-100-0,5.

Switch. A1 (current machine) - type. AE10-31 for current 10 A, SA1 type switch. PGZ (PG2), any button SB1 will do.

Relay K1 type KP460DC for 12 V (Polish production) or similar with three groups of changeover contacts rated for current up to 5 A. Relay K2 i. KZ type. RES47 passport RS4.500.407-01 (RS4.500.407-03).

For the manufacture of T1, transformer iron was used with a cross section at the location of the winding Sct = 35 cm. (the window has an area of ​​Sok=72 cm240). The primary winding contains 2,5 turns of PETV wire with a cross section of 1,8 mm22. (diameter 22 mm), secondary 3 + 10 turns with wire. PShV-XNUMX with a section of XNUMX mm square.

Any low-power transformer T2 (P - 5 W) with voltages in the secondary windings 3-4-5 - 18 + 18 V, and in 6-7-8 - 10 + 10 V, but it is better if its design provides for installation on a printed circuit fee.

Pulse transformer. T3 is carried out on the frame inside the armor cups of the standard size. B28 from ferrite brand M2000NM. The windings contain 1-2 - 80 turns, 3-4 - 40 turns with PELSHO wire with a diameter of 0,35 mm.

Schema setup

To set up, you need an oscilloscope, a digital voltmeter, an equivalent load Rh (wire resistor with a resistance of 1.1.2 ohms and a power of at least 100 W, for example, a nichrome wire with a diameter of 0,5 mm is suitable), as well as an external pointer ammeter (PA1) on current up to 2 A, see fig. 10.

Rice. 4.21. Connecting device circuits when setting up a circuit

Elements marked with an asterisk on the circuit diagram may require selection. The additional resistor R67 in the relay circuit is selected so that the armature of relay K1, after operation, is released at a supply voltage of less than 10 V (it is better to do this before the resistor and relay are installed in the circuit).

Preliminary configuration of the scheme is performed in the following sequence. It is necessary to temporarily block the relay contacts K1.1 and K1.2 with jumpers, and also unsolder R36. Set the SA1 switch to the "training" position, and bring the resistors R14 and R19 to the maximum.

Turning on the mains supply (A1) using an oscilloscope, check the shape of the sawtooth voltage at pin DA4 / 5 - it should not have a large step at zero level, see fig. 4.16, a (this may require the selection of resistor R28). After that, with an oscilloscope and a digital voltmeter, we control the voltage at terminals X1 and X2. The output voltage shape should correspond to that shown in fig. 4.16, b and be regulated by resistors R44 and R19. If this is not the case, then you should check the presence of pulses at the output of DA4 / 8 and the correct installation.

Rice. 4.16. The voltage shape at the control points: a) at the output DA4/5; b) on nests X1-X2 during setting; c) on sockets X1-X2 with the battery connected; d) at the exit DA4/8; e) pulses in the primary winding T3

With the trimmer resistor R44, we set the moment of opening the thyristors Uopen = 15,5 V. This is necessary so that in all modes of operation of the device the amplitude value of the output voltage exceeds the voltage on the battery (otherwise the thyristors will not open).

After turning off the device, solder R36 in place. After that, when the circuit is turned on, with the regulator R19 we set the effective voltage at the output of the device to 14,8 V and by selecting the resistor R36 we ensure that when this voltage is reached at the output, the comparator DA5 switches - +5 V appears at the DA9 / 15 output (the HL1 LED will glow) .

After that, with the regulator R19 we set a voltage of 10,5 V at the output of the device and by adjusting the resistor R41 we ensure that when this voltage is reached at the terminals X1-X2, the comparator has zero voltage at the output DA5.9 (resistor R41 sets the hysteresis value for the comparator).

In order for the controls installed on the front panel to be convenient to use, i.e. the range of output voltage adjustment by resistor R19 remained in the range of 10 ... 15 V - it is necessary to select additional resistors R15 and R24 Similarly, resistors R10 and R23 are selected for the range of adjustment of the current stabilization level by resistor R14 in the range of 1 ... 10 A. In this case allowable modes for the battery will not be exceeded.

Resistor R19 is used to adjust the voltage at terminals X1-X2 in the "start" mode, in other modes it is set to the maximum output voltage, since the circuit in these modes should work as a current stabilizer (the output voltage will depend on the current value) and as the battery is charged, the voltage on it will increase, but will not exceed the allowable value.

To calibrate the readings of the PA1 ammeter in the "charge" and "training" modes, it is necessary to set the instrument pointer to "38" with the resistor R0. Then we connect the Rh load (with the SA2 switch) and an external pointer ammeter (RA2), fig. 4.20. With resistor R14 (when R19 is at the maximum), set the current to 2 A using the external ammeter PA10, and with resistor R40 you need to set the same value of the current readings on PA1.

This operation should be repeated several times, adjusting R38 and R40 until the arrow PA1 at "0" and at a current of 10 A corresponds to the readings of the external ammeter.

Now you need to check the operation of the circuit in the current stabilization mode. To do this, at the time of turning on the device, we block contacts K1.1, K1.2. Set the SA1 switch to the "start" position, the current regulator "I" to the middle position, and "U" to the maximum. We connect a load with a resistance of about 1 Ohm to the output terminals X2-X0,2 (in terms of power, it should be designed for a flowing current of up to 100 A). In this case, the readings of the devices should be: RA1 - 50 A, PV1 - 10 V. The "I" regulator can change the output current - in this case, the output voltage will also change, which corresponds to the current stabilization mode. And when the load resistance changes within small limits, the current should not change.

On this, the preliminary adjustment can be considered complete, and the final check is performed on a real battery.

Author: Shelestov I.P.

See other articles Section Chargers, batteries, galvanic cells.

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