Powerful Affair of the Battery and the Alternator — Together Forever

I have been thinking about vehicle alternators lately, which is odd in that I have never been asked a car question about alternators. The subject of alternators has never come up at a dinner party or in casual conversation. No one tweets about alternators or “likes” articles about alternators.

But last August, I had an alternator event. I had purchased a new battery and had it installed in my 1997 GMC truck. Despite being equipped with this new battery, the battery voltage reading on my instrument panel kept dropping. My late husband’s son, Doug, who is a mechanic, was with me and he said it was the alternator.

We stopped at a local AutoZone and bought a voltage meter, which told us that the battery wasn’t getting any charge. When you think you have a bad alternator, turn everything off and drive immediately to your mechanic. You have a short window — maybe an hour — before your battery dies completely. Once my alternator was replaced the new battery charged properly.

The alternator is the source of electrical charge for your battery and your vehicle’s electrical systems. The current produced by the alternator is alternating current. Diodes in the alternator convert alternating current into direct current required by electrical systems and batteries.

Auto alternators use compact, electronic voltage regulators that decide how much current to send to the battery based on the battery’s level of discharge. The alternator keeps the battery charged and supplies voltage to the entire electrical system. The system is used for starting the vehicle, playing the radio, running the air conditioning or headlights.

If you’re alternator has electrical faults or poor wiring connection or if its belt is slipping or broken, then the battery will discharge. If you see that happening, if you notice your headlights dimming when you turn on the radio or use you windshield wipers, if have trouble starting your car, or you see a dashboard warning light then chances are the problem is your alternator.


“Today, with fancy headlights, quick-acting rear window defrosters, stereo system with multiple speakers, in-car television or DVD player, global navigation system and high output heating and air conditioning, the alternator and the battery are often hard-pressed to keep everything functioning. Demands can often far exceed the alternator’s capacity, leading to less than stellar performance from accessories — and ultimately to a dead battery,” said Fred Padgett, group product manager, starting and charging products for Bosch, the world’s largest automotive supplier.

The vehicle’s charging system should be checked every spring.  Winter and extreme temperatures can put a strain on the alternator, which should last in the range from 75,000 to 100,000 miles.

A patented new technology from General Motors called “Regulated Voltage Control,” or RVC, reduces the energy consumed by the alternator. It is being used to increase the fuel economy of GM’s new Chevrolet Cruze.

RVC reduces the power that runs to the alternator from 14 volts to 12.8 volts under normal driving conditions. This allows the alternator to focus the power on the vehicle’s electrical loads and avoid charging the battery with current it doesn’t need.
When the voltage sent to the battery is reduced, the demand on the alternator is reduced. That in turn reduces the alternator’s pull on the engine, which means the engine runs more efficiently. It gives the Cruze owner a 1.5 percent improvement on fuel economy or 8 more miles per tank.

I don’t know if people are going to start tweeting about liking car alternators, but maybe some readers will know what’s happening the next time their headlights dim when they turn on the radio. — Kate McLeod, Motor Matters

Bosch Alternator photo: New and remanufactured Bosch alternators carry the company’s exclusive free two-year emergency roadside assistance warranty in case the alternator fails. This provides the ultimate peace of mind for motorists and could be very valuable in the colder months.
Chevrolet photo: New electrical technology on 2011 Cruze reduces energy consumed by alternator, improving fuel economy by 8 miles per tank.

Copyright, AutoWriters Associates Inc., 2011

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