A simple battery charger. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A simple battery charger. 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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In recent years, a large number of chargers can be found on sale, which are based on various principles, including patented inventions. At the same time, battery chargers, made according to the so-called classical scheme, still have a considerable number of their regular adherents.

The figure shows a schematic diagram of a universal charger, when working with which you can set both the charging current and the output voltage. Any number of rechargeable cells with a maximum total voltage of 18 V can be connected to this charger.

Simple battery charger

It can be seen from the diagram that in this case we are talking about a classic sequential regulator on powerful transistors T1 and T2. In the proposed design, transistors of the 2N3055 type are used, but they can be replaced by any other npn powerful transistors that the radio amateur will have at his disposal.

After the mains transformer, the alternating voltage is rectified by diodes D1 and D2, after which it enters the IC1 microcircuit, which is a monolithic voltage regulator with an adjustable output. In this case, the desired value of the output voltage is set using the trimmer potentiometer PL.

The charging current through the serial regulator (transistors T1 and T2) is supplied to the output contacts, flows through the rechargeable battery and then to the case through the R8 resistor acting as a sensor, the resistance value of which is 0,1 Ohm. A voltage drop of 1 mV is formed across this resistor at a charging current of 100 A. This voltage in comparator IC2 type LM339 is compared with the voltage taken from the engine trimmer potentiometer P2, which is connected through resistor R6 to the output of the stabilizer IC3.

Since the voltage can be adjusted starting from zero using the trimmer potentiometer P2, the charging current of the battery, respectively, can be selected almost from zero.

The base of the transistor T3 is connected to the output of the comparator. If the charging current exceeds the selected value, then the voltage across the resistor R8 will also increase. In this case, the comparator will switch, which will lead to the opening of the transistor TK. As a result, the voltage at the output of the regulator IC1 will decrease and, as a result, at the bases of the powerful transistors T1 and T2. Changing the voltage at the bases of transistors T1 and T2 will reduce the battery charging current to the selected value. The transistor type 2N3904 can be replaced, for example, with transistors like BC337 or BC635.

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