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What is an alternator anyway. The name of the device gives us a clue as to what an alternator really is. It is a device that developes an alternating current. Now the device also contains some other components as well such as a diode bridge and a voltage regulator. And we will go farther into this in a few moments.

Years ago motor vehicles did not use an alternator. They used instead a device called a generator to keep the battery up to voltage. But there were draw backs to using a generator. And a generator was actually an electric motor reversed so that it was driven by a belt and producing electricity instead of consuming energy like a blower motor. But they were inefficient as a charging unit plus they used brushes in their construction which made them electrically noisy. Lot of static on nearby electronics like radios and tv’s was a really annoying side-effect of these devices.

For one thing they had to run at substantial revolutions in order to keep the battery up to charge. They also did not like heavy loads placed on them. Modern creature features such as power windows, deicers and heated seats would have quickly discharged your battery. And a generator would take a rather long time to recharge it. In today’s cars it is actually the alternator that supplies most of the electrical power for the car and not the battery as is commonly believed.

An alternator can easily provide, at idle speeds in excess of 100 amps of energy. Whereas an old-timey generator would be left far behind in this kind of contest. Let’s take a look inside the alternator. The alternator is composed of the field coils, the stator, the diode bridge and the voltage regulator. The field coils and stator are the actual power generating components. Just a lot copper windings wrapped around a metal shaft spinning in an electromagnetic field. Given how it is designed an alternator is able to generate a great deal of energy at low engine revolutions. But this energy is not direct current like the old generators were made to create. An alternator makes alternating current. Which is totally useless to your car unless something is done to it first.

And that is what the diode bridge is all about. More commonly known as a rectifier, a diode can take alternating current and convert it to dc or direct current. That current and voltage is then run through the voltage regulator which is designed to take that voltage and apply it to the battery if and only if there is a substantial voltage drop and the battery needs recharged. Otherwise the alternator just freewheels and runs any accessories the occupants may want.

Some signs your alternator may be going bad are a low initial charge on your in-dash meter when the engine is first started for the day. If your car has idiot lights you may notice the alt light stays on for a few minutes after you start the car. Or this light may come and go intermittently as you drive. Another problem an alternator may experience is seized bearings. You will have no warning usually with this problem. It seems to be alright until it suddenly stops your engine because the bearings have fused into an immovable mass and the alternator pulley refuses to turn. And no doubt the most common complaint found with an alternator is a complete lack of charge and a dead battery.

Replacing alternators is usually a rather straight forward job. You will need to disconnect the battery completely. Release and probably remove the serpentine belt. Disconnect any electrical connections to the alternator and then remove the bolts holding it on.

Once the new unit is on, replace the electrical connections and the belts and battery terminals and that is it. Start the car and watch the amp gauge or idiot light for any fluctuations. If your battery was a bit flat from not being charged correctly you can expect the amp gauge to show a pretty hefty charge going into the battery. And while you are under the hood, go ahead and check on the water level in the battery. Most people don’t realize it but an alternator that has a faulty voltage regulator could just as easily have been overcharging the battery and this will boil the water right out.