Monitor your Car battery or Inverter battery with this simple circuit. It always follows the terminal voltage of the battery and gives corresponding LED indications. A 12 volt Lead-Acid battery attains 13.85 volts in full charged condition and Inverter Tubular battery 14.85 volts. So it is necessary to have an idea about the charge status of the battery. If the battery discharges below 10 volts, it needs immediate charging to prevent the deep discharge. The circuit gives three LED indications. If the terminal voltage of the battery rises above 13.5 volts, Red LED lights. If the voltage drops below 10 volts, Green LED lights. If the voltage is normal around 12 volts, both the LEDs remain off.
IC CA3140 is wired as a Non inverting amplifier with VR2 for gain control. When the voltage in the battery increases above 13.5 volts (Gassing voltage above 13.85 is considered as over charged) output of IC1 turns low and Red LED lights. This indicates that the battery is entering into over charged state. When the voltage in the battery drops below 10 volts, output of IC1 goes high and Green LED lights to indicate the chance of deep discharge.
Before connecting the battery, set both the levels using a variable power supply. Provide 10 volts and adjust VR1 till Green LED lights. Increase the voltage to 11 volts, Green LED should turns off, otherwise adjust VR2. Increase the voltage to 13.5. Red LED will light.