Project Overview

This project was born out of necessity. Rather than replace an aged alternator early, this circuit was designed to monitor car battery voltage in real time to prolong the use of the alternator and detect eventual failure. The goal was to be able to detect operating voltages outside a specified range of 12-20 volts.

Note: My car’s name is Paula.

Alternator-Battery System

The alternators in most vehicles are essentially 3-phase electric motors. The alternator is spun by the main engine and creates 3-phase AC electric current. The AC current is run through a rectifier to get approximate DC current that is compatible with the 12 volt car battery. Typical alternator failure is caused by 1) rotor seizing and 2) phase shorting. In the event of a rotor seizing failure, there isn’t much that can be done. The battery will be dead shortly. The goal of the project was to bet on the latter failure considering many end of life alternators have winding erosion. In the event of the loss of a winding, the alternator will continue to charge the battery, however due to the rectifier, the current won’t be a constant DC value. This can cause damage to the battery and can be detected as battery voltage droop. An Arduino was programed to act as a voltmeter with an alarm. It measured voltage and set off a beeper in the event the voltage dropped.

Project Achievements

The circuit existed in my vehicle for many months. Upon getting pulled over by a State Trooper on one occasion, I had to explain the reason for a dash full of wires in a tangled mess that could be perceived differently to a person in charge of protecting people. He must have been intrigued by the utility because he let me off with a warning to slow down. In the end, the little gadget got me 6 extra months of carefree transportation before, one day, the beeper went off. I was on the way to work when the battery voltage dropped to approximately 11.8 volts. By the time I made it to the garage, it was just about dead.