Charger with timer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Charger with timer. 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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At present, with the development of MP3 sound reproduction technology, a lot of portable equipment powered by galvanic cells has appeared. Of course, it is more profitable to power a miniature MP3 player from batteries.

Chargers sold in stores are usually very simple and provide a fast charge mode, in which the battery ages much faster. It is safer to charge the battery with the nominal charging current (0,2 of the nameplate capacity), but this takes a lot of time, and this time must be controlled.

On fig. 1 shows a diagram of a self-made charger for charging "AA" and "AAA" finger batteries, which has a timer that allows you to set the charging time from two to ten hours. The time is set using a variable resistor, so the accuracy of the setting is not high, but an error of several minutes is not significant in this case.

Charger with timer

The charger itself consists of a constant voltage source of about 20V on the elements T1, VD1-VD4, C1 and a current stabilizer on the transistor VT1.

The value of the charging current depends on the resistance of the resistors R1 (for "AAA" batteries) and R2 (for "AA"). Selecting the type of batteries - switch S2. Charging occurs only when the transistor VT2 is open and, of course, the battery is connected. At the same time, the HL1 LED is on.

LED HL3 serves as an indicator of inclusion in the network.

The timer is made on chips D1 and D2. Elements D1.3 and D1.4 form an RS flip-flop. Charging occurs only when the output D1.3 is one (while VT2 is open). At the time of power-up, the R7-C5 circuit sets the trigger to zero at output D1.3 and one at pin D1.4.

At the same time, there is no charging, since VT2 is closed, and the timer does not work, since the unit at pin 6 of D1.2 slows down the multivibrator on the elements D1.1 and D1.2.

To start charging, you need to set the desired time with a variable resistor R5, press and release the S3 ("start") button. The counter D2 will be set to zero, and the trigger D1.3-D1.4 will be set to a position with a unit at the output of D1.3 and a zero at the output of D1.4. Now the transistor VT2 is open and charging is in progress, and the multivibrator D1.1-D1.2 is disinhibited. Pulses from it are counted by counter D2.

After a predetermined time, one appears at the highest output of the counter - pin 3. Capacitor C5 is discharged through R7 and one is sent to pin 8 D1.3. Trigger D1.3-D1.4 turns off charging and slows down the multivibrator. The key on VT3 opens, and the HL2 LED lights up - "Charged". This completes the charging.

If there is a power outage during charging, then after the restoration of power supply, the circuit will go into the off state (only HL3 is lit).

The circuit can be modified by introducing a backup source for microcircuits into it (Fig. 2).

Charger with timer

The backup source is a 9 V battery, Krona type.

You also need two diodes. Connect one in series with resistor R3, and the other in series with the backup source.

The Zener diode VD6 must be selected for a voltage slightly higher than the voltage of the backup source (D814V at 9,5 V). An additional transistor KT315 serves as a sensor for the presence of mains voltage. When there is voltage in the network, the voltage at its base is high, and it is open.

At pin 1 D1.1 is a logical zero, which does not interfere with the operation of the multivibrator. If there is no mains voltage, the transistor will close and through a 9,1 K resistor, a logic unit voltage will be applied to pin 1 D1.1, which will slow down the multivibrator.

The power switch S1 should now be double - one half of it turns off the mains, and the second (S1.1) serves to turn off the backup source.

Thus, with the modifications shown in Figure 2, when the mains voltage fails, the battery charging stops, but the D2 counter retains its state, and the time countdown stops.

Therefore, after the resumption of the supply of electricity, the charge will continue, and will last the remaining time. Even if the electricity is cut off several times during the charging time, the total charge time will be fully respected.

Details

Power transformer T1 - Chinese. He has conclusions from the mounting wires. The color is signed on the scheme. Thick wires - this is to the mains, and thin - from the secondary winding. Both windings are fully utilized.

Insulate unused taps from the middle of the windings. Chips K561 can be replaced by analogues of other CMOS series. Diodes KD209 can be replaced by any for a current of at least 0 A. Diodes KD522 - any low-power, for example, 1N4148. LEDs - any indicator. Choose replacement transistors according to power and conductivity.

The assembly is done on a 75x60 mm printed breadboard (transformer, bridge and C1 outside the board). Install the VT1 transistor on the radiator with a surface of at least 25 cm2.

Resistor R5 is desirable with a linear law of resistance adjustment (group A). You need to put a pen with an arrow on its shaft, and under it make a scale in units of time (from 2 hours to 10 hours, in increments of 30 minutes).

The accuracy of the timer, if necessary, can be set by selecting R4 and C2. At the same time, in order not to wait for several hours, the time interval can be controlled by the level at pin 4 D2. Here, the unit will appear exactly 128 times faster than on output 3. That is, the minimum interval of 2 hours is 53 seconds here, and the interval of 10 hours is 4 minutes 25 seconds. The time is measured from the moment the S3 button is released until one appears on this pin.

The charging current is set by selecting the resistances R1 and R2, respectively.

Connect a milliammeter instead of a battery and set a current equal to 0,2 of the nominal battery capacity by selecting the appropriate resistor.

Author: Shcheglov V.N.

See other articles Section Chargers, batteries, galvanic cells.

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