Automatic charger. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Automobile. Batteries, chargers
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It is advisable to supplement the charger for car batteries with an automatic device that turns it on when the battery voltage drops to a minimum and turns it off after charging. This is especially true when using the battery as a backup power or when the battery is stored for a long time without operation - to prevent self-discharge.
The proposed scheme turns on the battery for charging when the voltage on it drops to a certain level and turns it off when the maximum is reached.
The maximum voltage for acid car batteries is 14,2 ... 14,5 V, and the minimum allowable during discharge is 10,8 V. It is desirable to limit the minimum for greater reliability to 11,5 ... 12 V.
The proposed circuit (Fig. 1) consists of a comparator on transistors VT1, VT2 and a key on VT3, VT4.
Fig.1. Schematic diagram of the automatic charger
The scheme works as follows. After connecting the battery and turning on the network, press the button SB1 "Start". Transistors VT1 and VT2 close, opening the key VT3, VT4, which turns on relay K1. It, with its normally closed contacts K1.2, turns off the relay K2, the normally closed contacts of which (K2.1), closing, connect the charger (charger) to the network.
Such a complex switching scheme is used for two reasons:
- firstly, the isolation of the high-voltage circuit from the low-voltage circuit is provided;
- secondly, so that relay K2 turns on at the maximum voltage of the battery and turns off at the minimum, because. the applied relay RES22 (passport of the Russian Federation 4500163) has a switching voltage of 12 ... 12,5 V.
Contacts K1.1 of relay K1 switch to the lower position according to the diagram. In the process of charging the battery, the voltage across the resistors R1 and R2 increases, and when the unlocking voltage is reached on the basis of VT1, the transistors VT1 and VT2 open, closing the key VT3, VT4.
Relay K1 turns off, including K2. Normally closed contacts K2.1 open and de-energize the charger. Contacts K1.1 move to the upper position according to the scheme. Now the voltage on the basis of the composite transistor VT1, VT2 is determined by the voltage drop across the resistors R1 and R2. As the battery discharges, the voltage at the base of VT1 decreases, and at some point VT1, VT2 close, opening the key VT3, VT4. The charging cycle starts again. Capacitor C1 serves to eliminate interference from contact bounce K1.1 at the time of switching.
Adjustment of the device is carried out without battery and charger. An adjustable DC voltage source with adjustment limits of 10 ... 20 V is required. It is connected to the circuit terminals instead of GB1.
The slider of the resistor R1 is moved to the top position, and the slider R5 to the bottom. The source voltage is set equal to the minimum battery voltage (11.5...12 V). By moving the R5 engine, the relay K1 and the VD7 LED are turned on. Then, raising the source voltage to 14,2 ... 14,5 V, by moving the R1 slider, K1 and the LED are turned off. By changing the source voltage in both directions, make sure that the device is turned on at a voltage of 11,5 ... 12 V, and turned off at 14,2 ... 14,5 V. This completes the adjustment.
As R1 and R5, it is desirable to use multi-turn potentiometers of the SP5-3 type or the like.
Author: K. Selyugin, Novorossiysk; Publication: radioradar.net
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