When it comes to your vehicle's electrical system, many drivers assume that the battery is responsible for nearly everything. If you go out to your car in the morning and find that it's not starting, most experienced drivers will automatically assume that the car's battery is dead. However, there are other critical parts that could also be at fault in these situations, and one of these is the alternator.
The alternator essentially holds the electric charge before it goes to the battery. Without a properly functioning alternator, the battery won't receive any juice from the crankshaft, which generates the electricity in the first place. Think of the alternator as a mini storage facility for the electricity before the battery can distribute it to the rest of the vehicle.
Before this electricity can reach the battery, it must pass through the alternator's diodes, which are the most common cause of alternator failure. The diodes pass the electric current on to the positive battery cable, which eventually leads to the battery itself. However, the failure of the diodes to function properly will essentially disrupt this circuit. The diodes also serve to block any reverse electric current from reaching sensitive electronic equipment, which could lead to electrical issues.
Fortunately, vehicles also direct a small amount of current to a signal on the dashboard for the alternator. If the current does not reach this signal, the light on the dashboard will alert you to an alternator issue, so you should be able to check for potential problems - probably related to the diodes.
There are a number of reasons that diodes can go bad, but one of the most common is excessive current flow. If the connection is weak, the electric current will be forced to find a different path to the battery. This unregulated current usually gets to excessive levels, overheating the diodes and causing them to blow out. Using the alternator to power up an undercharged battery can also cause this issue.
Diodes can also be damaged through human error. For example, this is one reason why you should always turn off your car before replacing a battery. With electrical currents still pumping through the vehicle when the car is on, removing the battery will cause the electricity to overload the diodes. Another possible cause is jump starting a car - this may sometimes cause a surge that can overpower the alternator.