Charger 5...10000 mAh. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Rechargeable cells and batteries are often used to power portable devices. Their capacity may be different, so charging requires a different charging current. And the EMF, the achievement of which means full charge, depends on the number of series-connected cells in the battery. There is a need for a charger with wide ranges of these parameters.

The proposed device allows you to charge alkaline batteries with a capacity of 5 to 10000 mAh and batteries containing 2, 3, 4, 5, 6, 8, 10, 12, 14 or 16 cells connected in series. Further in the article, one term is used to refer to both rechargeable cells and batteries - a battery.

The device provides the ability to charge the battery with both intermittent direct current and asymmetric current of variable polarity. The method of charging with an asymmetric current was quite often considered in the literature, for example, in [1-3]. Much has been said about its advantages and disadvantages. Sometimes it allows you to restore a battery that has lost capacity. The charging current is set with a 11-position switch. The values ​​of this current are fixed: 0,5; 1; 2; 5; 10; 20; 50; 100; 200; 500 and 1000 mA. The desired value is usually numerically equal to a tenth of the nominal capacity of the battery, expressed in milliamp-hours.

The block diagram of the charger is shown in fig. 1. The generator generates rectangular pulses. They are fed to the input of the distributor, which forms time intervals for measuring the EMF of the battery, its charging and discharging. These three intervals form one charging cycle. Their durations when charging with an asymmetric current are related as 1:2:2, where the first digit is the relative duration of the EMF measurement, the second is the relative duration of the charging current 1c, the third is the relative duration of the discharge current 1p. When the asymmetry is off, this ratio is 1:2:0 (discharge interval is excluded), the charging current is intermittent.

Rice. 1. Structural diagram of the charger

The measurement of the EMF of the battery being charged occurs when the stabilizers of the charging and discharging current are turned off. It is followed by a voltage comparator. When the rated EMF is reached, it is triggered, as a result of which the control unit stops the distributor in the EMF measurement state. He can stay there indefinitely. If the battery EMF drops, the distributor will restart and charging will begin.

The values ​​of the charging and discharging current set the appropriate stabilizers, depending on the position of the switch in the device. In this case, the charging current is always ten times greater than the discharge current. To simplify the pairing of charger microcircuits with current stabilizers, their power supply is made bipolar with respect to a common wire. The stabilizers themselves are also fed with bipolar voltage, and the positive voltage is adjustable depending on the number of cells in the battery being charged. This allows you to reduce the power dissipated by the charging current stabilizer when charging high-capacity, but low-voltage batteries.

The charger circuit is shown in fig. 2. On the elements DD1.1, DD1.3, DD1.4, a pulse generator with a frequency of about 150 Hz is assembled. They go to the counter DD3, which is made of the pulse distributor. Diodes VD5 and VD6 perform a logical OR function for signals from outputs 0 and 1 of the counter (pins 3 and 2), thus forming a time interval for measuring the battery emf. Four diodes VD7-VD10, performing the same function for signals from outputs 2-5 of the counter (pins 4, 7, 10, 1), form the charging current flow interval. Four more diodes VD11-VD14 combine the signals from the remaining counter outputs, forming a discharge interval.

Rice. 2. Charger circuit (click to enlarge)

As already mentioned, the EMF measurement of the battery being charged is performed when the charging and discharging circuits are disconnected from it. Upon reaching the nominal EMF, the voltage level at the output of the voltage comparator at the op-amp DA1 becomes high (about +15 V). This voltage through the limiter of the resistor R22 and diodes VD3 and VD4 is supplied to one of the inputs of the element DD2.2. On it and on the elements DD1.2, DD1.5 and DD2.1, the distributor control unit is assembled. A logically high level set at the input (pin 5) of the DD2.2 element by a comparator, and the same level that came to the second input (pin 6) of the same element from the distributor in the EMF measurement interval, put the DD2.2 element into a low level state at the outlet, which stops the distributor in the EMF measurement position.

To securely fix the distributor in the stopped state, the comparator DA1 is covered by positive feedback through the resistor R20.

This coupling creates a small hysteresis in the switching characteristic of the comparator, which increases its noise immunity. The EMF at which charging stops is 1,35 ... 1,4 V per battery cell. This level is regulated by a trimming resistor R19.

You can also charge batteries with an EMF at which charging should be stopped, different from that installed in the charger, but then you will have to follow the charging process yourself. Switch SA2 in the closed state excludes the influence of the comparator DA1 on the operation of the distributor, as a result of which it continues to work regardless of the EMF of the battery being charged.

Diodes VD1, VD2 and resistor R21 protect the input circuit of the op amp from high voltage damage. The exemplary voltage source for the comparator consists of resistors R1-R11 and switch SA1.1. The numbers indicating the switch positions correspond to the number of cells in the battery being charged.

The logic element DD2.3 inverts the charging signal from the distributor, the DD1.6 element inverts it again, amplifies the current and supplies it to the base of the transistor VT6, which controls the charging current stabilizer. The charging permission is signaled by the HL1 green LED.

Element DD2.4 inverts the signal of the discharge interval from the distributor before applying it to the base of the transistor VT7, which controls the discharge current stabilizer. The fact that the operation of this stabilizer is allowed is signaled by the yellow HL2 LED. When the battery charging is completed, the HL1 LED goes out, and if it was performed in the asymmetric current mode, the HL2 LED also goes out. Diodes VD15 and VD16 limit the reverse voltage at the bases of transistors VT6 and VT7 when they are closed.

You can turn off the asymmetry of the charging current with the SA3 switch. When its contacts are closed, the DD2.4 element blocks the signal for turning on the discharge current stabilizer, and the elements DD1.2, DD1.5 and DD2.1 form a signal that switches the distributor to the EMF measurement state. Therefore, there is no discharge interval in the charger cycle, and the charging current is intermittent. Only the HL1 LED is lit.

On transistors VT1, VT3 and VT4, a charging current stabilizer is assembled. The current value depends on the resistance of the resistors R29-R42, selected by the switch SA4.1. Transistors VT2 and VT5 stabilize the discharge current, depending on the resistance of resistors R47-R59, selected by switch SA4.2.

The diagram of the power supply unit of the charger is shown in fig. 3. Most of the supply voltages are obtained from the alternating voltage of the winding 3-5 of the transformer T1, rectified by the bridge diodes VD19. The voltage regulator +/-15 V for powering the op amp DA1 is made on zener diodes VD21-VD24 and resistors R62, R63. Zener diodes VD26, VD27 and resistors R64, R65 form a +/-4,7 V voltage regulator for digital circuits.

Rice. 3. Diagram of the power supply unit of the charger (click to enlarge)

To power the charging current stabilizer, a VD20 diode bridge rectifier with step-by-step adjustment of the rectified voltage is used. It is produced by switching the taps of the secondary winding 6-10 of the transformer T1 with the SA1.2 switch paired with SA1.1. The discharge current stabilizer is powered from the winding 11-12 of the transformer T1 through an unstabilized rectifier on the VD25 diode bridge.

The charger is assembled in a steel case with dimensions of 180x200xx165 mm. Its front panel contains all the switches, LEDs and battery terminals. The holder of the fusible insert VPB6-1 (FU1) is installed on the rear panel and the power cord is brought out. Inside the housing there is a T1 transformer and a 170x190mm circuit board. A heat sink ribbed on one side with dimensions of 80x80 mm is attached to the board, on the flat side of which transistors VT3-VT5 are fixed without any gaskets.

Transformer T1 with a power of 30...40 VA is made of a material designed to power halogen lamps. It has a toroidal steel magnetic core. Its primary is retained and its 12V secondary removed. Winding 3-5 is wound with PEV-2 wire with a diameter of 0,28 mm and contains 180 turns with a tap from the middle. The voltage on each half of this winding is 14 V. Winding 11-12 consists of 39 turns of the same wire, its voltage is 6,6 V. Multi-pin winding 6-10 is wound with PEV-2 wire with a diameter of 0,67 mm. There are 132 turns in total - 33 in each of the four sections. The voltage between pins 6 and 10 is 22 V. Between pins 9 and 10 is 5,5 V, between pins 8 and 10 is 11 V, between pins 7 and 10 is 16,5 V.

Switches SA1 and SA4 - PM 11P2N, switches SA2, SA3 - MT1 or similar imported, SA5 - TP1-2. As clamps XT1 and XT2 for connecting a rechargeable battery GB1, a spring connector for acoustic speakers with two clamps - red and black - is used. The positive pole of the battery is connected to the red clamp, the negative pole to the black one.

The device uses fixed MLT resistors, a tuning resistor SP3-38a, oxide capacitors K50-16 and similar imported ceramic capacitors K10-7v. Diode bridges KTS407A and RS107 can be replaced by others with similar parameters.

Start setting up the device with a selection of resistor R26. To do this, connect a multirange milliammeter to terminals XT1 and XT2. Then connect the base with the emitter of each of the transistors VT6 and VT7 with two wire jumpers. Selecting the resistor R26, achieve the absence of current through the transistor VT2.

Before adjusting the charging current stabilizer, connect the collector and emitter of the VT6 transistor with one wire jumper, and the base and emitter of the VT7 transistor with the other. Follow the readings of the milliammeter in each position of the switch SA4. If the current differs significantly, by more than ± 5%, from the required one, then by selecting the appropriate resistor, bring it to normal.

Check the discharge current stabilizer in the same way, but by connecting the base of the VT6 transistor with its emitter, as well as the collector with the emitter of the VT7 transistor, with jumpers. The discharge current must be ten times less than the charging current set by switch SA4. If this is not the case, select the appropriate resistors in the discharge current stabilizer.

After performing the described operations, do not forget to remove all jumpers. Now you need to adjust the threshold EMF at which charging will stop. To do this, connect the plus to the XT2 terminal, and the minus to the XT1 terminal, an external adjustable stabilized voltage source loaded with a resistor, for example, 100 Ohm, 1 W. Set the charging current to 4 mA with the SA2 switch, and the number of charged elements equal to six with the SA1 switch, move the trimming resistor R19 engine to the minimum resistance position (left according to the diagram). With a tuning resistor, achieve a sure shutdown of the charging current at an external source voltage of 8,1 ... 8,4 V. The HL1 LED, and if the SA3 switch is on asymmetric charging mode, and the HL2 LED should go out when this voltage is exceeded.

In order to obtain acceptable EMF values ​​for stopping charging after this adjustment in other positions of the SA1 switch, you need to select resistors R1-R11 with resistance values ​​as close as possible to those indicated in the diagram, or use high-precision resistors.

Literature

1. Skrindevsky N. Automatic battery charger. - Radio, 1991, No. 12, p. 28-30.
2. Yakovlev E. Low-voltage automatic charger. - Radioamator, 2005, No. 7, p. 21.
3. Konovalov V. Pulsating charger-recovery device. - Radio amateur, 2007, No. 5, p. 30, 31.

Author: A. Vishnevsky

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