Charger with electronic protection. Encyclopedia of radio electronics and electrical engineering

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

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Rectifier diodes in chargers can be damaged if the output terminals are accidentally shorted or the battery is connected incorrectly.

The usual means of protection is fuses, however, to restore the device to working capacity, this requires replacing a blown fuse with a new one, which, as usual, is not at hand at the right time. We have to put a "bug", which further reduces the security of the charger.

The device eliminates the flow of charging current if the voltage at the output terminals is below a certain value.

Thyristor VS1 is unlocked by the collector current of transistor VT1 when the instantaneous value of each half-wave of the rectified pulsating voltage exceeds the battery voltage. If the voltage at the output terminals is zero, which can be caused by a short circuit, or small in magnitude, due to the connection for charging, for example, a 6-volt battery instead of a 12-volt battery, or the polarity of the battery connection is incorrect, then the transistor VT1 is closed and the thyristor remains in a non-conducting state.

The device also protects the battery from overcharging, since increasing the voltage on the latter when fully charged leads to the reverse bias of the thyristor and its closing.

This unit can be an addition to an existing charger, but the secondary voltage of the mains transformer must be increased by about 1 V to compensate for the voltage drop across the thyristor.

For the operation of a charger designed for a number of voltages, it is advisable to use a resistance box as a resistor R5, switched simultaneously with the switching of the transformer windings. The resistance of the resistor at a lower voltage should be proportionally reduced, and at a higher voltage it should be increased.

Author: Shelestov I.P.

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