Rechargeable batteries should not be discharged below a certain voltage level. This lower voltage limit depends upon the type of the battery. This simple circuit can be used for 12V batteries to give an indication of the battery voltage falling below the preset value. The indication is in the form of a flickering LED
All rechargeable battery has their specific level of charging and discharging, they are likely to get damage if the battery voltage exceeds that level. Here is a simple circuit battery voltage monitor used to indicate the state of battery by monitor them. Circuit description of battery voltage monitor
The circuit of battery voltage monitor is fabricated and designed around op-amp IC LM709 configured as comparator. Where bi-color LED is used as indicator and indicates three voltage level state of a 12V battery. Resistor R1 with potentiometer VR1 is used as potential driver of voltage monitor circuit.
When voltage level rise above 13.5 volts, the output from IC1 goes low as a result LED begins to emit RED light. Similarly, when the voltage fall below a preset level (10Volts) the output goes high and the LED start to emit GREEN light. Resistors R3 and R4 is used as current limiter of LED.
NOTE: Adjust VR1 such that LED begins to emit GREEN light when 10V DC is connected.
Resistors (all ¼-watt, ± 5% Carbon)
VR1 = 10 KΩ (Potentiometer)
IC1 = LM709; D1 = 1N4003
B1 = 12V Battery; LED = Bi-color LED