Here is a dual charger for Inverter battery. It can charge the battery via Solar panel as well as from AC power to keep the battery always in top condition. Even though a 12 volt Solar panel gives around 20 volts in full sunlight, it is available only three or four hours in a day. During the remaining hours, the intensity of light is very low and the condition worsens in cloudy and rainy days. This results in incomplete battery charging that ultimately leads to memory effect and permanent damage of the battery. This charger shifts the charging to AC mode when the voltage from solar panel reduces below 12 volts and restores the solar charging when the sunlight is sufficient enough again.
The circuit uses a voltage comparator built around IC1. It is powered by the voltage from the solar panel and ZD1 provides 12 volts regulated supply to the circuit. Its Inverting input is referenced at 10 volts using a 10 volt Zener while the Non inverting input receives a variable voltage through R3, VR1 and R4. When the solar panel gives more than 12 volts output, pin3 of IC1 gets a higher voltage than pin2 ( as set by VR1) and its output turns high. T1 conducts and the relay energizes. The battery gets charging voltage through the Common and NO contacts.
Click Image to get enlarged view
When the solar panel output reduces to 12 volts, output of IC1 turns low and the relay de-energizes. Then the battery charges through the Common and NC contacts of the relay. The NC contact is connected to the Transformer power supply using a 15-0-15 volt 1 Ampere transformer .If the switch S1 is closed, the AC charging continues during night also.