Understanding The Operation Of Your Auto's Alternator

By Roger Mooremen

Imagine this scenario: it's raining outside. You're leaving the office after a hard day and are looking forward to arriving at home. You climb into your car and crank the engine. Within a few minutes, you're on the highway with a 30-minute trip ahead of you. The radio is keeping you company while the heater warms the cab. Fifteen minutes into your drive home, your radio begins to cut out. Soon, the heater also becomes cranky. With several miles to go, your headlights begin to dim. Before long, your engine has died. You're still miles from home and the rain has only worsened. These are the signs of a dying alternator.

Even though this component receives little attention, it is one of the hardest-working parts under the hood. Below, I'll explain how it works and a few factors that can end its life. I'll also provide a few tips for finding a replacement.

How The Component Works

Most people believe the electricity that powers their vehicle comes solely from the battery. In truth, the alternator creates the electricity. It's a common misconception, especially given that this part works so closely with the battery to produce power. While you're driving, it keeps the battery charged so it can deliver power throughout your car. It is in constant operation. If it dies, so too, does your battery. This is why parts and systems, such as your heater, radio, headlights, and engine eventually stop working.

When Things Go Wrong

Your vehicle's alternator is comprised of several moving parts. That makes the entire assembly vulnerable to the buildup of debris, which in turn can lead to heat, stress, and ultimately, failure. For example, the needle bearings (part of the rotor) can break down from excess heat. When this happens, you might hear a grinding sound. The alternator can also fail if you attempt to jump-start your battery after it has completely lost its charge.

In some cases, this component can start to overcharge or undercharge the system. If the system is overcharged, you'll notice your lights failing suddenly rather than dimming. If the system is undercharged, your lights will dim, your engine will start to miss (or be sluggish when you're cranking it), and you'll eventually hear a fast-paced machine gun sound.

The only way to fix the problem is to buy a replacement.

Finding A Budget-Friendly Replacement

The cost of an alternator is partially dependent on your vehicle's make and model. It is also dependent on whether you purchase a new component versus a rebuilt or remanufactured unit. Automotive experts have differing opinions regarding the pros and cons of buying a rebuilt or remanufactured unit. On the one hand, doing so is less expensive. However, there is no way to know whether a rebuilt unit will last. Many drivers have discovered that the cost savings associated with purchasing a rebuilt evaporate because they fail more quickly than a "from the box" new model.

My advice? If your alternator fails, invest the money to purchase a new or remanufactured OEM unit. It will cost a few extra dollars than a rebuilt, but you'll have confidence that it will last for years. - 29952

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