Is the alternator charging your battery properly?

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A water-cooled automotive alternator that has been removed from its engine. Why someone added water cooling is anyone's guess.

A water-cooled alternator. (Photo Credit: CC BY/Chris Bede/Flickr)

Your car’s alternator is a generator. It’s the link between the gas tank and battery, converting mechanical energy from the serpentine belt into electrical energy that tops off the battery and powers on-board devices. It is important that your alternator works correctly, or the battery charge will run out more rapidly. Rather than becoming stranded, here’s how to check whether your alternator is properly charging the battery.

Things you’ll need to check your alternator

In order to determine whether your alternator is providing a proper charge to your battery, the first things you’ll need are, obviously, your car’s battery and alternator. If you own a drivable vehicle, you have both of these. You’ll also need a voltage meter. These are available at stores like Radio Shack for as little as $10. Auto batteries range from $50 to $150 or more, while an alternator retails for $120 or more new, a third of that reconditioned. For safety while under the hood, protective eyewear is also encouraged.

Begin the testing process

First, start the vehicle. If you notice that the headlights are still dim after turning the brightness dial to maximum, the alternator is starting to give. However, if the lights brighten when you rev the engine, that’s a sign that the alternator is working properly. At this point, turn off all extraneous electronic equipment in the car, such as lights, radio, A/C, heater or anything else.

Now turn off the car. Check the wire connections between the alternator and the battery to ensure they are secure. While you’re at it, inspect the alternator belt. If it appears shiny or cracked, replace it immediately.

Bringing in a battery charger

After inspecting the connections, turn on the ignition once more. If the car fails to start, a battery charger will be necessary. Buy one new from $50 to $150, depending upon the options you want.

If the engine does turn over, connect your voltage meter to the positive and negative terminals of your battery. Let the engine idle and then check for a reading. Between 13.6 and 14.3 volts is a good range. If the number is lower, you will likely need a new or rebuilt alternator.

Whatever you do, if you notice the alternator is dying but the engine still turns over, don’t wait. Go get a new battery and alternator, because the engine may not start again unless you do so.



Mister Fixit

Bad alternator sound

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