Free Automotive Repair Advice by Certified ASE Technicians
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 the battery is charged by the alternator which is driven by the engine.
While in operation the alternator creates electricity, about 13.6 to 14.3 volts,
and recharges the battery to it's 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 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 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.
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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