Using this circuit diagram can be made a very simple car charger which delivers a constant current output. Constant current supplied by the battery car charger can be applied to battery from the board lighter socket.
Charger consists of a network transformer Tr1, bridge rectifier B1 and filtering capacitor C1. Charge current passing through the regulator IC1 and switching resistances in series is: 107 mA (47 ohms) at 230 mA (22 ohms), 500 mA (10 ohms) 1 A (5 ohms).
Diodes D1 D4 indicate switch position. Transistor T1, R1 and diodes D5 ensure constant illumination.
When the battery is connected, the relay is actuated and the circuit is disconnected from the network.
When the battery is connected, it loads C3, T4 opens and activates the relay. Coupling occurs at the network and battery will be charged by D7. Voltage drop on D7 determine the opening of T3 and T2, so the relay remains activated. The transistor T4 is blocked, or the collector to +12 V. The resistor R5 C3 remains charged, so that the transistor T4 is locked.
For the charger can operate with exhausted batteries, can S1 can be shunted, which allows connecting the manual charger.
Circuit Diagram Schematic: