Charger for car batteries. Scheme, description

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Charger for car batteries. Encyclopedia of radio electronics and electrical engineering

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

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The service life of a car battery depends not only on its quality, but also on proper operation. Some motorists believe that if you drive a car constantly, then everything will be in order with the battery. However, driving around the city is associated with a fairly frequent launch of the starter and a small mileage "from point A to point B". As a result, the battery does not have time to renew the spent energy, it is undercharged, and this, in turn, leads to sulfation of the plates and loss of nominal capacity. For example, after two years of operation of a new battery, I measured its capacity, and it turned out to be less than 50%.

In some articles, the authors recommend fully charging the batteries only before winter operation, but it seems to me that this should be done more often - 2-4 times a year. Moreover, before the final charging, it is necessary to train the battery (2-3 discharge-charge cycles). The charge is best carried out in a desulfating way, i.e. Charge for 30 seconds with a current of 0,1C, then discharge for 10 seconds with a current of 0,01. C (C is the nominal capacity of the battery).

I offer a charger (Fig. 1), which provides automatic and manual modes. Consider the operation of the device in manual mode. After applying 220 V and turning on SA1, a reduced voltage appears on the winding II of the transformer T1, which is rectified by the diode bridge VD16 and filtered by the capacitor C14. Relay K1 and stabilizer D3 are powered from this bridge, the voltage from which is supplied to power the microcontroller D5.

(click to enlarge)

Charger for car batteries

From the windings III and IV of T1, voltage is supplied to the diode bridge VD5 and voltage stabilizers D1 (+12 V) and D2 (-17,6 V), from which operational amplifiers D4 and D7 are powered. From the winding V T1, the voltage is rectified by the diode bridge VD9 ... VD12, filtered by the capacitor C7 and serves to power two parallel current sources of the ITUN type (voltage controlled current source) D7.1, D7.2, VT3.VT6, R9.R12, R30, R31, C17, C18, which are controlled by PWM pulses from pin 5 of the D5 microcontroller. From the winding VI T1, the voltage is rectified by the diode bridge VD1, filtered by the capacitor C4 and stabilized by the D6 microcircuit. From this microcircuit, the battery discharge control circuit (ITUN), consisting of D4.1, VT1, VT2, R1.R4 C1, C2, is powered. This ITUN is controlled by PWM pulses from pin 3 of D5 through a decoupling optocoupler VS1.

On the operational amplifier D4.2, a battery voltage control circuit is assembled. Resistors R13, R14 form a voltage divider, the R17.R20 chain serves to shift the level of the measured voltage by subtracting the reference voltage from the voltage on the battery. Diodes VD13, VD14 protect the input of the analog-to-digital converter of the microcontroller D5. An indicator is connected to pin 2 D5 on HL2, VT8, R32 ... R34 and a transistor switch on VT7, VT9, R35, R37, R38, which turns on relay K1. The HL2 indicator indicates the modes:

mode. STOP or manual - HL2 off;
battery discharge by an external load is enabled - HL2 is constantly on;
charging - HL2 flashes (long on, long off);
desulfation - HL2 flashes at a higher frequency (short ignition, short-term extinction).

Button SB1 puts the device in STOP mode, SB2 performs START, i.e. the device is switched to charge mode or to cyclic (charge-discharge). The SB3...SB6 buttons set the current in the charge (discharge) mode. The SB7 button, after turning on the device, puts it into the desulfation mode (at the same time, the HL2 LED lights up for a short time).

In the desulfation mode, the battery is discharged to a voltage of 10,2 V by an external load (HL1 lamp), then charged with a current of 5,5 A for 30 s and discharged with a current of 0,55 A for 10 s. The cycles are repeated until the voltage on the battery stops increasing within 2 hours. Then the current decreases to 2,75 A and additional charging takes place for another 2 hours. If the voltage starts to decrease, the charging is turned off.

In manual mode, the battery is charged with a current of 5,5 A to a stable voltage on the battery for 2 hours. Buttons SB3...SB6 can change the charge-discharge current. current indication is carried out by a RA1 milliammeter with the SA2 switch set to the "A" position (in the "V" position, the voltage is controlled).

Attention! The battery should be connected to the charger only after the power is turned on, otherwise the transistor VT2 may fail.

The device uses a transformer TS 180. The primary winding is retained, and the rest are unwound. First winding V -50 turns of wire PEV-2 01,5 mm, then winding II - 26 turns of wire 0,5 mm, winding VI - 20 turns 0,3 mm, windings III and IV - 50 turns 0,4 mm each .

Indicator RA1 - М2001/1-М4, which needs to be slightly improved. In it, the initial position of the arrow is shifted to the right from the real zero, a shunt R8 is connected to the head and the scale is recalibrated using a control ammeter. It is also necessary to calibrate the voltage values \u6b\u7band select resistors RXNUMX or RXNUMX.

Any relay with an operating voltage of 12 V and a contact current of 4 ... 5 A can be used in the device. The circuit is assembled on a printed circuit board made of one-sided fiberglass with dimensions of 38x98 mm. The drawing of the board is shown in Fig.2.

Charger for car batteries

The microcontroller contains a microprogram whose HEX codes are presented in the table.

Before operation, the device must be set to cut-off voltage during discharge. To do this, disconnect the output of the resistor R13 left according to the scheme, connect a laboratory power supply to it and supply a voltage of 10,2 V from it. The device is started in automatic mode, while the relay and the HL1 light turn on. Rotate the engine of the tuned resistor R19 until the relay is turned off.

This completes the setup and checks the performance of the entire device.

Author: Abramov S.

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