EagleTribune.com, North Andover, MA


May 18, 2014

New alternator will likely be sturdier

I have a 2000 Honda Accord EX V-6 with a little more than 44,800 miles on it. In February the alternator failed and was replaced. I would love to learn more about this incident. Is this a once-in-a-lifetime event? I hope so. I have a friend who also had alternator failure when she was 200 miles from her destination in northern California. Thanks to her cellphone, she got help.

Let’s take a look at what alternators do, and how they work, before putting your mind at ease.

Virtually all motor vehicles built since the 1960s employ an alternator, which generates electrical power for the entire vehicle. The battery simply stores energy, and is used for engine startup, engine-off accessory use, and serves as a voltage stabilizer, and a backup — for a limited time, should the alternator fail while driving. With minimal electrical accessory usage, one might drive perhaps several hours with a just-failed alternator. Don’t shut off the engine until reaching a safe place, as the starter requires a lot of battery energy.

Alternators get their name because the electricity generated inside alternates between positive and negative polarity. AC current is great for powering devices, but cannot be stored. A group of diodes within the alternator rectify the AC current into DC (constant polarity) current before sending it out for vehicle use and to the battery for storage.

Alternators convert belt-driven mechanical energy from the engine into electrical power. The more electrical power that is needed, the greater the load on the belt and engine. The drive belt must be in good condition and properly tensioned, or alternator performance will be compromised. Also, heavy electrical use reduces fuel economy, as the engine must work harder to turn the alternator. For this reason, recent vehicles employ smart operating strategies similar to those used in hybrid vehicles, emphasizing alternator usage during coasting and braking conditions when engine slow-down is desired.

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