Charging rechargeable lights from the on-board network of the car. Scheme, description

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Charging rechargeable lights from the on-board network of the car. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Automobile. Batteries, chargers

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The proposed device is intended for charging pocket rechargeable flashlights with a built-in charger (charger) from the vehicle's on-board network or another source of direct voltage 12 ... 14 V. From a similar device described in the article by S. Gureev "Device for charging rechargeable flashlights from the on-board network car" ("Radio", 2007, No. 8, pp. 49, 50), the proposed one is distinguished by half the number of parts and much smaller dimensions.

The principle of operation is described in detail in the mentioned article, briefly it boils down to the following. As a rule, the built-in flashlight chargers contain a rectifier and a ballast capacitor. Its capacity determines the charging current (and hence its duration) and is designed for an alternating voltage of 220 V with a frequency of 50 Hz. To provide the required charging current at a lower alternating voltage, it is necessary to proportionally increase its frequency. The described device is a rectangular alternating voltage source with an amplitude of about 10 V and a frequency of several kilohertz. Thanks to this, charging can be carried out without modifying or disassembling the flashlight (if, of course, the charging current of the battery is known), using its standard plug, designed to be connected to a 220 V network.

Charging rechargeable lights from the vehicle's on-board network
Fig. 1

The scheme of the device is shown in fig. 1. Its basis is a pulse generator assembled on a TDA7052 (DA1) chip, which is a AF bridge amplifier with a voltage gain of 38 ... 40 dB and a maximum output power of 1,2 W (at a load with a resistance of 8 ohms). Due to positive feedback through the circuit R1C2R2C3 (passive band-pass filter), oscillation occurs at a frequency of about 10 kHz. Anti-phase voltage pulses with this frequency and a duty cycle of about two through trimmers R3 and R4 are fed to the XS1 socket, to which the rechargeable flashlight is connected. The first of them sets the charging current (its maximum value is about 75 mA), the second acts as a current sensor, in parallel with which the HL1 LED is connected - an indicator of the charging process. By changing the brightness of its glow, the course of the process is judged: at first, the battery voltage is minimal and the LED glows noticeably, and as it charges, it increases, due to which the current through the LED decreases and the brightness of its glow decreases.

Charging rechargeable lights from the vehicle's on-board network
Fig. 2

A drawing of a printed circuit board on which all parts are mounted, except for the XP1 plug and the RJ1 fusible insert, is shown in fig. 2. It is made from one-sided foil fiberglass with a thickness of 1 ... 1,5 mm. The board is designed for the use of fixed resistors P1-4, MLT, S2-23, tuning resistors SPZ-19a, an oxide capacitor (C1) from Jamicon and ceramic K10-17 (the rest). Resistor R2 is installed above the DA1 chip. The XS1 socket is an instrument type, upon completion of the installation of the parts, it is glued to the board (Fig. 3), and the terminals of the sockets are connected with short lengths of tinned wire to the printed conductors.

Charging rechargeable lights from the vehicle's on-board network

The device is connected to the car's on-board network with a two-wire cord ending in a standard plug inserted into the cigarette lighter socket. A fusible insert for a current of 0,2 A is mounted in the plug. After checking the performance and adjusting, it is advisable to cover the board with the parts with a layer of epoxy glue to protect it from moisture and damage.

Setting up the device begins with setting the required charging current. To do this, a flashlight with a charged battery is connected to the device, the engine of the tuning resistor R3 is moved to the extreme right (according to the diagram) position, and the resistor R4 is moved to the extreme left and the supply voltage is applied. Resistor R3 sets the required charging current, and resistor R4 achieves a weak glow of the HL1 LED. Since the adjustments are interrelated, operations with these resistors will have to be repeated two or three times. If it is not possible to set the required current, it is necessary to increase the frequency of the generator by replacing C2 and C3 with capacitors of a smaller (necessarily the same) capacity.

If the technical characteristics of the flashlight battery are unknown, then the charging current provided by the standard charger when connected to a 220 V network is preliminarily determined. To do this, the flashlight will have to be disassembled and the current in the battery circuit measured in charging mode.

Author: I. Nechaev, Moscow; Publication: radioradar.net

See other articles Section Automobile. Batteries, chargers.

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