Circuit diagram of 12V lead acid battery monitor

This circuit is designed to monitor the charge level of a 12V lead-acid battery. Battery level will be indicated by LED.

This simple circuit allows monitoring of the charging process to a higher level. Final adjustments are simple and easy, and the only equipment required is a digital voltmeter to ensure important accuracy and reliability. Connect an input voltage of 12.65 volts between the positive and negative terminals and adjust the 10K trimpot until LED10 lights up. Lower the voltage and all other LEDs will light up in sequence. Check that LED1 lights up at approximately 11.89 volts.

The battery is fully charged at 12.65 volts or higher and is considered "empty" at 11.89 volts. A green LED indicates the battery capacity is over 50%, a yellow LED indicates a capacity of 30%–50%, and a red LED indicates less than 30% capacity. This circuit with the components shown uses less than 10mA.

You can modify this circuit to suit your needs by making minor modifications. The circuit diagram above is set to "DOT" mode, which means only one LED is lit at a time. If you wish to use "BAR" mode, tie pin 9 to ground, but this will obviously increase current consumption. The LED brightness can be adjusted up or down by selecting different values ​​for the 4K7 resistor connected on pins 6/7

You can also change it to monitor voltage levels. For example, let's say you want to change to 10–13 volts, you connect 13 volts to the inputs (+ and -) and adjust the 10K potentiometer until LED10 lights up. Temporarily change the resistor on pin 4 with a 200 kilohm potentiometer and reconnect 10 volts to the input. Now, readjust the 200K potentiometer until LED1 lights up. When you are satisfied with the adjustment, feel free to replace the 200K potentiometer with a resistor again. (obviously after measuring the resistance of the potentiometer).

Diode 1N4007 is included to protect the circuit from incorrect polarity connections. However, it is strongly recommended to connect the monitor directly to the battery, in principle a connection to the cigarette lighter is sufficient, but for currently unknown reasons the voltage at this time is 0.2 volts lower than the voltage measured directly on the battery. Maybe some residual resistance caused by the ignition switch and the path through the fuse?