What is the voltage output of a healthy alternator?
Around 14 volts (between 13.8 and 14.2 is good). Remember, modern alternators will have their output controlled by an ECU and may not always output this voltage.
How can I identify a fault?
Perform a voltage check. If the voltage of the alternator increases or decreases with engine speed, then it may indicate a fault. You could also switch on heavy electrical loads to make the alternator work hard and check to see if the voltage output of the alternator operates consistently at around 14 volts.
What happens if the voltage output is too high or low?
Too high means that the vehicle’s battery is being overcharged. Too low means the regulator is potentially faulty and is discharging the battery.
What’s the difference between a standard alternator and a smart charging system?
An alternator delivers full power, even if it’s not needed. This is inefficient as it wastes fuel and causes more pollution than necessary. A smart charging alternator’s output is variable and controlled by an engine management system. This means that it only delivers the power that the vehicle needs.
How can I tell if the engine is fitted with a smart charging system?
If the engine is Euro 5 emissions standard or later, it mostly likely has a smart charging system. The other indicator is the battery sensor found on the negative terminal of the battery – smart charging systems often have these.