Automatic Inverter Battery Charger with Cut Off

This Battery charger can replenish any kind of 12 V Inverter battery or Car battery and keep it in top condition. The charger never allows the battery to Over charge or Deep discharge. It automatically charges the battery when its terminal voltage drops below 12 volts and switch off the charging process when the terminal voltage rises to 13.5 volts. So that the battery can be kept unattended.

Internals of an Inverter

Fig. 1: Image of a Inverter Battery

Working of the circuit is too simple. The 15-0-15 – 1 Ampere step-down transformer with its rectifiers D1 ,D2 and smoothing capacitor C1 provides 15 Volt DC to the Three terminal variable voltage regulator IC LM317. It can handle up to 1.5 ampere current and can vary the output voltage from 1.2 volts to 37 volts. The output depends on the feedback from the output pin (pin 3) to the adjust pin (pin1) of LM 317. By adjusting VR1 it is easy to set the output voltage from 1.2 V to 15 V DC. The charging current depends on the values of R1 and R4 and around 300 milli amperes current is available for charging at 15 volt DC.

When the output is available from IC1, Green LED lights and current flows through diode D3 and resistor R4 to the battery provided the battery voltage is below 12 volts. Zener diode will not conduct in this state since the battery takes all the current for charging. When the terminal voltage of battery rises to 13.5 volts, the current flow to the battery ceases and Zener gets breakdown voltage and it conducts. The current from the Zener forward bias T1 so that all the output current from LM 317 will be drained through T1 to the ground as indicated by the Red LED. This stops the charging process. Charger remains in this state till the battery voltage drops below 12 volts (break down voltage of Zener). If this happens Zener turns off and T1 switched off allowing output current from LM317 to pass into the battery for charging again.

Battery is just like a Baby. It requires continuous attention and care. Click on the following links to read the articles related to batteries and maintenance.