Car Repair Help by Professional Mechanics
How Does it Work /
Alternator
Alternator and Charging System
A battery is needed to power the operating system of your car. Once the
vehicle is running an alternator that is driven by the engine charges the
battery. While in operation the alternator creates electricity, about 13.6 to
14.3 volts, and recharges the battery to its original state of charge. The
alternator is one of the hardest working electrical components in your vehicle.
When your vehicle is running the alternator is busy creating electricity to
provide the engine and the car accessories with needed power. When the car is
not running and your battery is severely discharged some electrical components such as alarms or
other memory retaining items may still operate or operate poorly. Typically,
these components are designed to operate properly at 12 volts; if the system
voltage is low it can cause erratic symptoms.
Typical Alternator
Common Problems and Solutions
When jump-started a severely discharged battery can cause the alternator to
overload and internally fail. If this occurs replace or charge the battery
before replacing the alternator. This will help prevent a second alternator
failure. Most vehicles use a multi-ribbed belt connected to the engine to rotate
the armature inside the alternator. If the belt fails it should be replaced
immediately. Belt tension should be taught. If it isn't, check the belt
tensioner, it may need to be replaced or the incorrect size belt may have been
installed. Either of these conditions can cause the vehicle to stall and not
restart.
Additionally, problems can occur if the alternator is overcharging the
system. Some symptoms of overcharging include a swollen or seeping battery, both
headlight bulbs failing at the same time, and other
electrical component problems. To perform an
alternator system check for this condition use a voltmeter on both positive
and negative terminals while the engine is idling. If the voltmeter reading is
over 15 volts this is an indication of an overcharging alternator. The
alternator should be replaced with an OE (original equipment) unit. While an
inferior rebuilt alternator is often much cheaper, it can fail prematurely
causing another costly replacement.
The most common alternator problem is "undercharging." This condition is
often accompanied by symptoms such as a low state of charge on the battery, poor
or erratic performance from electrical components and dim headlights and other
lighting systems. The first symptom of an undercharging alternator is a slow
cranking engine. The next symptom is a "machine gun" sound when the engine is
cranked as the system voltage drops below normal operating levels. In order to
correct this problem a replacement alternator must be installed after the
battery has been replaced or charged.
Maintenance
To ensure that your alternator lasts as long as possible there are several things
you can do. Be sure all battery connections are tight and both terminals are clean.
This should be inspected periodically regardless of when the battery was changed
as even new batteries can have problems and be defective. While the engine is off,
visually inspect the alternator belt and replace the belt if cracks or
tears are observed.
How Does it Work
/ Alternator
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