Simple charger for four batteries. Encyclopedia of radio electronics and electrical engineering

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

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At present, batteries NkHz-0,45, D-0,26 and others are increasingly used in various designs as batteries. Shown in fig. 5.11 transformerless charger allows you to simultaneously charge four D-0,26 batteries with a current of 26 mA for 12 ... 16 hours.

Fig. 5.11

The excess mains voltage of 220 V is extinguished due to the reactance of the capacitors (Xc) at a frequency of 50 Hz, which makes it possible to reduce the dimensions of the charger.

Using this electrical circuit and knowing the charge current (1c) recommended for a particular type of battery, using the formulas below, you can determine the capacitance of capacitors C1, C2 (total C \u1d C2 + C2) and select the type of zener diode VD0,7 from the reference book so that its stabilization voltage exceeds voltage of charged batteries by about XNUMX V.

The type of zener diode depends only on the number of simultaneously charged batteries, so, for example, to charge three cells D-0,26 or NkHz-0,45, it is necessary to use a VD2 type KS456A zener diode. An example of calculation is given for batteries D-0,26 with a charging current of 26 mA.

The charger uses resistors of the MLT or C2-23 type, capacitors C1 and C2 of the K73-17V type for an operating voltage of 400 V. Resistor R1 can have a rating of 330 ... 620 kOhm (it ensures the discharge of capacitors after the device is turned off).

You can use any LED HL1, while choosing a resistor R3 so that it glows brightly enough. Diode matrix VD1 is replaced by four diodes KD102A.

Fig. 5.12.

The topology of the printed circuit board with the arrangement of elements is shown in fig. 5.12. The board is single-sided (without holes), and the elements are installed from the side of the printed conductors.

When using the elements indicated in the diagram, the charger is easily installed in the housing from power supplies for pocket microcalculators (Fig. 5.13) or can be placed inside the device housing where the batteries are installed.

Rice. 5.13. Charger housing

Indication of the presence of voltage in the charge circuit is carried out by the HL1 LED, which is placed in a prominent place on the case. Diode VD3 allows you to protect the discharge of batteries through the charger circuit when it is disconnected from the 220 V network. When charging batteries NkHz-0,45 with a current of 45 mA, resistor R3 must be reduced to a value at which the LED glows with full brightness.

It is better to check the charger when connecting instead of batteries measuring instruments and an equivalent load (Fig. 5.14), the minimum value of which for four batteries is determined by Ohm's law:

R \u4d U / I \u0,026d 150 / XNUMX \uXNUMXd XNUMX Ohm, where

U - voltage on discharged batteries (for the bulk of batteries, this value is one volt per cell).

Rice. 5.14. Equivalent load for charger setting

When using the charger, it is necessary to monitor the time, since the above circuit, although it reduces the likelihood of the battery receiving an excess charge (by limiting the voltage with a zener diode), however, it does not completely exclude such a possibility, with a very long charge time. And if you do not have problems with memory, then this simple and small device will help save money.

The second circuit of the transformerless charger (Fig. 5.15) is designed to simultaneously charge two batteries of the type NkHz-0,45 (NkHz-0,5). It provides an asymmetric charge mode, which allows you to extend the life of the batteries. The charge is made by a current of 40...45 mA during one half-wave of the mains voltage. During the second half-wave, when the corresponding diode is closed, the element G1 (G2) is discharged through the resistor R4 (R5) with a current of 4,5 mA.

Fig. 5.15

The batteries G1 and G2 are charged alternately, so, for example, during the positive half-wave, G1 is charged (G2 is discharged). Such a construction of the circuit allows the process of charging the batteries independently of each other, and any malfunction of one of them will not disturb the charge of the other.

To indicate the presence of mains voltage in the circuit, a miniature lamp HL1 type CMH6.3-20 or similar is used. Batteries should not be left connected to the circuit for a long time without the charger being connected to the mains, since in this case they are discharged through resistors R4, R5.

If the device is properly assembled, no configuration is required.

Rice. 5.16. Power supply circuit diagram with automatic charger (click to enlarge)

The scheme shown in fig. 5.16, in contrast to the above, excludes damage to batteries due to their receiving an excess charge. It automatically turns off the charging process when the voltage on the elements rises above the permissible value and consists of a current regulator on the VT2 transistor, an amplifier VT1, a voltage level detector on VT3 and a voltage regulator D1.

The device can also be used as a power supply for current up to 100 mA by connecting the load to pins 1 and 2 of plug X2.

The indicator of the charge process is the glow of the HL1 LED, which goes out when it is completed.

We start setting up the device with a current stabilizer. To do this, we temporarily close the base of the VT3 transistor to a common wire, and instead of batteries, we connect an equivalent load with a milliammeter 0 ... 100 mA. By controlling the current in the load with the device, by selecting the resistor R3 we set the rated charge current for a particular type of battery.

The second stage of tuning is to set the output voltage limitation level using the tuning resistor R5. To do this, by controlling the voltage at the load, we increase the load resistance until the maximum allowable voltage appears (5,8 V for four D-0,26 batteries). With resistor R5 we achieve a current cutoff in the load (the LED goes out).

In the manufacture of the device, you can use a case from a power source BP2-3 or similar (it is also convenient to take a transformer from it). The transformer is suitable for any small-sized one with a voltage in the secondary winding of 12 ... 16 V.

Transistor VT2 is attached to the heat dissipating plate. Capacitors C1 are used type K50-16-25V, C2-type K50-16-16V. For ease of setup, it is advisable to use a multi-turn resistor of the SP5-5 type or similar as R2, the rest of the resistors are suitable for any type.

You can get voltages of 6 or 9 V from the power source if you install KR1EN142B (G) or KR5EN142A (G) in place of the D8 chip, respectively.

Publication: cxem.net

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