Universal timer for charger. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Universal timer for 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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Usually, the main parameters for charging batteries are two quantities - charging current and time. For example, in the instructions for a lead-acid battery, it will be written something like: "charge with such and such a current for such and such a time."

Simple chargers are usually a source of current, but the time has to be controlled "manually", that is, by a timer, chronometer, alarm clock, cuckoo clock. The following describes a simple timer that is designed to turn off the charger after some time after being turned on.

Since I wanted to make this timer universal, it is made independently powered from the mains through a miniature low-power power transformer. With fire protection circuits, the circuit is designed so that after the end of the time delay, the entire system is disconnected from the network - both the timer and the charger.

This eliminates the possibility of ignition of the power transformer from too long operation, and also excludes the possibility of spontaneous switching on of the charger as a result of drops and temporary voltage drops in the network.

The schematic diagram is given in the figure.

Universal charger timer

The basic part of the circuit is IC K176IE12. This microcircuit is widely known to radio amateurs, its functional purpose is a generator of second and minute pulses for electronic clocks, as well as for dynamic indication, signals. Here it operates at much lower frequencies, which is necessary to obtain large time delays with the same counter, and an RC circuit is used instead of a quartz resonator with a multivibrator built into the microcircuit. Exposure adjustment, setting range change, all this is done by changing the parameters of this RC circuit.

The ranges are switched by switch S3, one section of which switches capacitors C4 and C5, and the second one switches resistors R4 and R5.

Resistors need to be switched because the ranges have different overlap widths (1-24 and 1-60). S3 is shown at the 1-24 o'clock position. The start of the timer begins with the zeroing of the counter. Here, this happens automatically when the power is turned on, since pins 9 and 5 of the microcircuit are connected to the C2-R1 circuit.

When the power is turned on, the C2 charge creates a pulse on these pins and resets the counters. Turning on / starting the timer is carried out by the S1 button. When pressed, it supplies power to both the timer and the load, which can be the mains input of the charger. In this case, the K176IE12 counters are reset, and a low logic level is set at the output of the senior counter (pin 10). This is equivalent to applying voltage to the base VT1.

The transistor opens and the relay K1 included in its collector circuit closes its contacts, indicated in the diagram "S2". Now, even after the button is released, the load and the primary winding of the transformer will remain on.

Next, the countdown begins and after the interval set by resistor R3 and switch S3, at pin 10 K176IE12, the voltage increases to a high logic level. Transistor VT1 closes. Relay K1 turns off its contacts S2, and everything is disconnected from the network.

LED HL1 - power indicator. Relay K1 can be used almost any with a winding of 12 V and a resistance of at least 50 ohms. In this case, this is a relay for the instrument panel of a VAZ car.

The T1 transformer is ready-made Chinese with a secondary winding of "9-0-9 V", that is, 18 V with a tap strictly from the middle. Therefore, the rectifier is made according to a full-wave circuit.

If there is a transformer with one winding for 8-10 V, then the rectifier must be made according to the bridge circuit.

Only a multivibrator needs to be adjusted. It is necessary to select the resistances R4, R5, as well as the capacitances C4 and C5. You need to select the values so that on the range "1-24 hours" (S3 in the position as in the diagram), the frequency at pin 13 of the microcircuit is regulated within 14-350 Hz, and on the range "1-60 minutes" - within 0,35 -21 kHz.

This completes the setup. It remains only to mark the scale around the handle of the variable resistor.

Author: Rufinov P.

See other articles Section Chargers, batteries, galvanic cells.

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