Many alternator repairs involve removing the defective unit and replacing it with a new or rebuilt one, and this is often the most cost effective solution. In some cases the voltage regulator may be replaced, especially if it is an external part. Other alternator repairs can involve removing the unit, opening it up, and replacing or fixing internal components, such as the windings, brushes, bearings, and commutator. A problem that appears to be associated with the alternator can also involve loose or corroded connections, a bad battery, or other issues.
In order to determine whether alternator repairs are required, a few simple tests are typically performed. The battery is usually charged and tested first because it can be difficult to get accurate readings from the alternator without a proper input voltage. Unlike older generators, alternators require constant battery voltage in order to run properly. A bad battery can potentially damage an alternator by forcing it to work without this input voltage or by making it work too hard. If the battery appears to be in good condition, the voltage and amperage output of the alternator are typically tested at several engine speeds and load conditions.
The most common repair associated with alternators is replacement. If the alternator is not putting out the required voltage or amperage, the most cost effective way to rectify the situation is often to acquire a new or rebuilt unit. In order to replace an alternator, the serpentine or v-belt must usually be removed. Any electrical connections to the alternator must also be removed, after which the bolts and brackets that connect the unit to the engine can be taken off.
Many older vehicles used voltage regulators that were not integrated with the alternator. Early examples of these used mechanical switches, though newer versions have solid state components, such as transistors. When the voltage regulator fails, the alternator will no longer function properly. If the voltage regulator is not inside the alternator, it is typically easy to remove and replace. In some cases, a regulator that is mounted on an alternator can also be replaced without removing the unit from the vehicle, though this is less common.
Other types of alternator repairs require that the unit be removed from the vehicle and opened up. Since this is a labor intensive process, it is common for the alternator to be rebuilt at this time instead of simply replacing a single component. Common alternator repairs that can be performed after the unit is opened up include replacing the brushes, cleaning the windings, and replacing rectifier diodes. The bearing may also be pressed out, especially if it was making any noise.