![]() ![]() If the voltage is above 12 V the zener Z3 will bias the transistor TR1 sufficiently to turn it on and this will light the second LED D2 which is green and indicates that the battery voltage is normal. The first LED D1, is connected in series with R2 and D4 and will light when the battery voltage is below 11.5 V. The principle behind the circuit is very simple. board and can be fitted easily anywhere in the dashboard. The whole circuit is accommodated on a small p.c. When the red LED is on the battery voltage is low, green is the OK signal and orange is a warning that the battery is overcharging. It uses three LED’s to give a visual indication of the state of charge of your car battery. The power supply to the 741 op amp is unipolar 12V regulated DC.įig.This is a really useful instrument for your car. ![]() Resistor (0.5K, 9K, 2 watt) (9K if not available may be split to three 3K ) The power rating of the resistors should be above 2 Watt. only 3V.So the extra 9V should be dropped across somewhere. ![]() ![]() Let the value of each resistor be R.īut we need to monitor voltage from 9V to 12V i.e. There should be six identical resistors across each op amp. The value of the resistors is calculated as:Īssume current ‘i’ flowing through the voltage divider is 1 mA. If the voltage goes down below 9V, the transistor will be activated and the buzzer will start indicating LOW VOLTAGE Similarly if the battery voltage is 9.2V only the LED at the bottom will be ON and other 5 will be OFF. The series of resistors connected at the inverting terminals of each op amp makes a voltage divider and exact comparing voltage is supplied to each op amp.įor example if the battery voltage is 10.7V, the upper 2 LEDs in the circuit will be OFF and the lower 4 LEDs will be ON. Comparison is done between the two terminals of each op amp and accordingly output is shown. So 6 op amps are used to compare and display the appropriate level of voltage. Here for the development of the circuit, the 12V to 9V range is divided into 6 parts as 9V, 9.5V, 10V…11.5V. My point to say all these is that to monitor a 12V battery, it is sufficient to monitor the battery voltage from 12V to 9V range and a voltage below 9V should give a warning for LOW BATTERY VOLTAGE. Any inverter designed to use with a 12V battery should be comfortable to produce a constant AC output voltage during the fall of battery voltage from 12V to 9v approximately. So it is generally considered that if the output voltage of a 12V battery changes from 12V to 9V approximately, it is constant and after the voltage falls below 9V, it is considered to be discharged and need to be charged again. Practically, it is not possible and the output voltage of the battery decreases gradually as load connected to it draws current from it. Generally a 12V battery is expected to produce a 12V dc voltage all the time until it gets discharged. The series of resistors connected at the inverting terminals of each op amp makes a voltage divider and exact comparing voltage is supplied to each op amp. Here for the development of the circuit, the 12V to 9V range is divided into 6 parts as 9V, 9.5V, 10V.11.5V. My point to say all these is that to monitor a 12V battery, it is sufficient to monitor the battery voltage from 12V to 9V range and a voltage below 9V should give a warning for LOW BATTERY VOLTAGE. ![]()
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