Car Battery And Alternator Monitor Circuit

The monitor is a simple voltage comparator in which a car battery serves as the battery for operation. The input voltage to the comparator is set by adjustment potentiometer PI, which must be adjusted so that the green LED L2 is on when the alternator is operating properly and red LED1 is on when the alternator is inoperative.The circuit operates as follows: When the alternator operates properly, the battery voltage is higher and PI is set so that transistor Ql causes Q2 to be off. That results in Q3 and Q4 being fully on, thus applying current to green LED L2. If the battery voltage is lowered (alternator inoperative),

transistor Ql is turned off. That allows transistor Q2 to turn fully on, applying current to red LED LI, indicating trouble. Once Q2 is on, it causes Q3 and Q4 to go out of conduction.

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