How Do Alternators Work? - And How to know if Yours is Failing

An alternator is the power base of your vehicle – it provides the electrical energy required to run essential components like fans (engine cooling, air conditioning), ignition coils, and nonessential components like car stereos, interior lights, and cigarette lighters. Most people believe that power comes from the battery, and to some extent that is true. However, the power that runs all of those electrical components actually comes from the fuel used to run the vehicle. Essentially, the electrical power is generated by your crankshaft. It turns your fan belt which then rotates the alternator. The primary function of the alternator is to convert the power from the gasoline engine that drives you along the road to electrical energy. This keeps your battery fully charged and provides the electricity required to power all your electrical needs.

How can you tell when your Alternator is no longer working?

Initially, you may not notice anything because the battery will continue to provide enough electricity to continue running the engine and the above-mentioned electrical components for a period of time. A bad alternator is not going to immediately leave you on the side of the road. Still, if you were driving and knew your alternator was failing, it would be important to conserve power by turning off the stereo, blowers, and headlights (if you could do so safely). The battery reserve power might allow you to get home or to a local garage.

One major problem that will occur when your alternator is failing will be the lack of voltage to keep the engine running properly. This happens as the battery loses the last of its reserve power.

How can you tell if the alternator is failing without taking it apart and doing some measuring inside the alternator?

It's really pretty simple. You will need a simple voltmeter. You can get one at an electronics store for less than ten dollars. To tell whether or not your alternator is failing, follow these next steps. Start the car, make sure all the accessories are off and rev up the motor to a fast idle. Set the voltmeter to the DC scale (not AC or Ohms). Measure the voltage across the battery terminals – a red lead of the voltmeter on the positive terminal, black on the negative (ground in most cars). The voltage should read around 14 volts. If it reads less than 12 volts, you may indeed have a failed alternator and may need a new alternator, you can skip the next step. Next, turn on the heater, the rear window defroster, stereo, headlights and anything else that draws power. Now rev up the motor and watch the voltmeter. It should still be reading around 14 volts. If it reads lower than 13 volts, your alternator is likely not in the best condition and you may want to consider a replacement alternator.

The last indication of alternator failure can be found in the noise it makes. The rotor inside the alternator rotates on bearings; these can be high precision bearings, and they can fail. If they do, you will hear a loud grinding noise coming from the alternator. To isolate the noise, get a length of tubing; any garden hose will do fine. Put one end to your ear, and move the other around in the vicinity of the alternator. The noise will be much louder when you point it at the alternator if that is the culprit. Other possibilities are the water pump and the power steering pump which are also driven by the engine belt. To further isolate the noise, disconnect the drive belt and spin the alternator by hand. If you hear a rumble or grinding noise, then the bearings are broken. If you don't hear a noise, the problem may still be in the alternator since the bearing might be quiet without the loading of the drive belt tension. Check for side play.

Hopefully, this article has helped you determine if you are in need of a new alternator (replacement alternator)