DIY: car battery and alternator voltage tester.

 

Put an LED voltage tester from a breadboard to a printed circuit prototype board and then into a car cigarette lighter enclosure. Voltage can be measured from 6 to 16 V in a 2 V increament. Red LEDs are for 6, 8 and 10 V. Green LEDs are for 12, 14 and 16 V. 

Voltage inputs from a voltage source at 8, 12 and 16 V are shown in pictures 2, 3 and 4.

Picture 6 is the tester in a car cigaretter when the car key is utility mode (krey is one stop (or push the start button once, radio is on and engine is off).

Picture 5 is when the car engine is running. 

A car battery voltage should be 12.6 V when the car is not running.

A car alternator should be 14.4 V when the engine is running.