Automatic charger for automotive lead-acid batteries

Fig. 1. Automatic charger. Scheme

This scheme allows you to automatically charge the car batteries.
Charging current through the battery depending on the voltage on it, applied to the B-Z transition of VT1, is regulated by transistor VT1, collector voltage which is controlled by charge indicator on the LED. As the charging current of the charge gradually decreases and the LED goes out, but a powerful compound transistor containing VT2, VT3, VT4, rose. Resistor R3 limits the maximum charging current, so it must be powerful enough, not less than 10 watts, probably better than wire.
Moment of full battery charge (and a decrease in charging current to zero) determines the necessary tension on it - usually enough 14,2-14,5 V. Electro-chemical potentials of the materials used lead acid batteries can be fully charged battery at the same voltage.
This threshold is set resistor R1, the threshold depends on the type of transistors used.