What it Does
The vehicle’s charging system is responsible for supplying all of the electrical power that the vehicle needs once it has started. It supplies power for any electrical item in your vehicle that you could think of, and it also keeps your battery charged. If you’re wondering why some electrical functions work when the vehicle is off (charging system inactive), this is because the battery and the charging system are joined together, and the battery can supply power while the vehicle is not running.
Why This Matters
Charging system failure can cause the vehicle to break-down. Loss of power to the engine management system will cause the engine to stall. A depleted battery may be able to keep the engine running (for a time) as long as the car remains on but be unable to restart the car if it’s turned off. This means that charging system failure can actually cause an on-the-road break-down or a surprise failure to start.
Possible Problems and Concerns
Alternator Failure
The alternator is the heart of the charging system. It generates the voltage and amperage necessary to keep vehicle systems powered up. High quality alternators commonly last for several years and beyond 100,000 miles, but it’s not uncommon for a vehicle to need one (maybe even two) alternators replaced over the course of a 300,000 miles (or higher) lifespan.
Alternator Control System Failure
Many alternators are only going to provide charging system voltage if they “know” that they are supposed to. Circuit failure (wiring, connection, or circuit board) resulting in the alternator regulator lacking for proper power or ground, or not getting a “wake-up” command or signal, can result in a healthy alternator that does not do its job.
Voltage Loss
Circuit troubles (bad wiring or connections) can cause loss of charging system voltage. For example, a healthy alternator generating 14.5 volts can only provide 11.5 volts to the battery if 3 volts drops through a bad alternator cable. In a condition like this, the battery will not stay charged.
Belt Failure or Slippage
Alternators require rotational motion to work so a failed belt drive will disable the alternator. A slipping belt will spin the alternator, but belt slippage can result in reduce alternator RPM and thus partial loss of alternator output.
Installation Errors
Improperly secured alternators may not sit level with the belt drive line, and this can result alternator bearing failure. Alternators that are not fully secured have resulted in damaged engine computers due to voltage spikes. Alternator belts that are not properly run-in or tensioned are at risk of premature slippage or wear.
Poor Battery Condition
The alternator will work harder if it keeps having to charge a weak battery that keeps losing its charge. A bad battery may also pull excessive current from the alternator just to “keep itself charged,” which will work the alternator harder as well. Both conditions can reduce alternator lifespan.
Mis-Diagnosis or Assumptions
While alternator failure is always a possibility when a charging system fails, it is one among other possibilities. Proper testing & evaluation methods can determine exactly what has failed, and they may also uncover deeper issues or secondary issues: for example, a loose connection, worn belt, bad grounding point, or weak battery.