This battery charger can replenish any type of 12V inverter battery or car battery and keep it in the best condition. The charger never allows the battery to over-charge or deeply discharge. It automatically charges the battery when the terminal voltage drops below 12 volts and shuts down the charging process when the terminal voltage rises to 13.5 volts. So that the battery can be kept unattended.
The operation of the circuit is very simple. The 15-0-15 – 1 Ampere step-down transformer with its rectifiers D1, D2 and smoothing capacitor C1 supplies 15 Volts DC to the three-terminal variable voltage regulator IC LM317. It can handle current up to 1.5 amps and can vary the output voltage from 1.2 volts to 37 volts. The output depends on feedback from the output pin (pin 3) to the tuning pin (pin 1) of the LM 317. By adjusting VR1 it is easy to set the output voltage from 1.2V to 15V DC. The charging current depends on the values of R1 and R4 and about 300 milliamps of current are available for charging at 15 volts DC.
When output from IC1 is available, the green LED lights up and current flows through diode D3 and resistor R4 to the battery, provided the battery voltage is below 12 volts. The Zener diode will not conduct in this state as the battery draws all the current to charge. When the terminal voltage of the battery rises to 13.5 volts, current flow to the battery stops and the Zener obtains breakdown voltage and conducts. The Zener current forward biases T1 so that all of the LM 317's output current is drained through T1 to ground, as indicated by the red LED. This stops the charging process. The charger remains in this state until the battery voltage drops below 12 volts (Zener breakdown voltage). If this happens, the Zener shuts down and T1 shuts down, allowing the LM317 output current to pass to the battery for charging again.
The battery is like a baby. Requires continuous attention and care. Click on the following links to read articles related to batteries and maintenance.
Circuit diagrams
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