ALT-1 How an Alternator Works
The alternator is a key accessory to any internal combustion engine. It provides all of the electricity for the engine, including the starter, fuel pump and fuel ignition system, and charges the vehicles battery too. In addition, when the engine is running the alternator furnishes electricity to power all other electrically operated systems and devices in the vehicle.In older vehicles a generator was used to generate electricity, but with the advent of inexpensive semiconductor rectifiers in the 1950’s, alternators began to replace the more expensive generators. The only real difference between a generator and alternator is the method by which the Alternating Current (A/C) electricity is converted into Direct Current (D/C) electricity. In a generator the A/C to D/C conversion is accomplished by a multi-contact rotating mechanical switch called a commutator. In the Alternator, as already eluded to, the conversion is facilitated by semiconductor diodes arranged in a bridge rectifier configuration. The alternator method provides two advantages, lower manufacturing cost and elimination of brushes which would otherwise require periodic replacement.The alternator converts mechanical energy into electrical energy. Once the engine is running, a v-belt transfers mechanical energy from a larger pulley mounted on the engines crankshaft to a smaller pulley mounted on the alternator shaft. The different sized pulleys cause the alternator shaft to spin several times faster than the crankshaft rotations per minute (rpm).The stationary field windings installed in the alternator casing are initially energized by current from the vehicle battery producing a magnetic field around the rotor mounted on the alternator shaft. The rotor basically consists of a number of windings or loops of wire. Each winding produces 1 volt of electricity, therefore, the total number of windings in the rotor will be proportional to the designed alternator output voltage. Most vehicles today use a twelve volt system. As the rotor shaft turns, the loops or windings pass through the magnetic field generated by the field windings, inducing an electric current flow in the rotor windings. This current is fed by slip rings to the rectifier which converts the A/C coming from the rotor into D/C for distribution and use by the vehicles D/C electrical systems.Once the engine is running the alternator provides current to the field windings. If you have a dead battery, one way to eliminate the alternator as a possible source of the problem is to disconnect the vehicle battery while the engine is running. If the engine keeps running and you can turn the lights and other electrical accessories on, the alternator must be working and the source of the problem is either the battery it self, possibly a faulty voltage regulator, or a short somewhere in the electrical system that is draining voltage from the battery when the engine is turned off.
