How to Troubleshoot an Auto Alternator
Auto alternators are very reliable and rarely need maintenance. However, they are an important part of an auto, and if they don't operate correctly, it can result in your battery going dead and your electrical equipment not working. If you find yourself getting these problems, then you need to troubleshoot the problem. Follow through on a few moderately easy checks and tests, and you can find out the problem and get it rectified.
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Instructions
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Check Alternator Belt Tension
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Check the tension of the alternator belt. If an alternator belt is too loose, the alternator pulley doesn't spin effectively, meaning it doesn't produce enough electricity to charge the battery and power the electronics.
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Find the longest part of the alternator belt. This is usually between the alternator and the water pump.
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Place a 6-inch ruler in the center of the longest part of the alternator belt. Make a mark on the ruler where the belt is using a pen.
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Keep the ruler in the same place using one hand then using your other hand push and pull the alternator belt so it moves across the ruler.
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Measure the total distance you can move the belt. If your alternator belt is correctly tensioned, you can only move it about one-half to 1 inch each way: total movement shouldn't exceed 2 inches. If it moves more than 2 inches, the belt is too loose and the tension needs tightening, or at worst you need a new belt. Get it checked out by your auto garage if you're not confident about doing it yourself.
Check Alternator Wiring Connections
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Check the wires that connect to the terminals of the alternator. The number of wires varies, depending on auto type.
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Use your fingers to try and move each wire. If you can move the wires, it's likely you have a bad electrical connection.
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Tighten the wires onto the terminals. Use a wrench or screwdriver, depending on how they connect. If you find broken or exposed wire, then get it checked out professionally.
Test Alternator Voltage Output
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Check you don't have any loose clothing. Start the engine.
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Set your multimeter to measure voltage. Place the prong on the end of the red wire that's attached to the multimeter onto the positive terminal of the battery. The terminal is labeled "+" or "Pos." Place the prong on the end of the black wire from the multimeter onto the negative battery terminal. It's labeled "-" or "Neg."
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Read the multimeter display. It will read between 13.4 and 14.5 volts if the alternator is working correctly. If it's less than 13 volts get it checked out by a professional. The reason the output voltage is greater than the battery voltage (12 volts) is because the volts travel through thick cables before they reach the battery, causing electrical resistance. The extra voltage compensates for the resistance.
Test Alternator Ampere Output
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Check the ampere output your alternator should produce if it's working properly. Find the specifications section in your owner's manual. This is usually at the back. Find the alternator information, and note the ampere range. As a guide, most car alternators produce between 50 and 100 amperes, depending on the electrical requirements of the car.
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Set the multimeter to measure amperes. Repeat the process you completed to measure voltage by placing the prongs on the battery terminals as before. Read the multimeter display. Make a note of the reading.
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Turn on energy consuming electrical equipment in your car such as wipers, heater fan and lights. Repeat the test to check the amperes using the same process. Read the display, and make a note of it.
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Turn off the electrical equipment in the car, and turn off the engine. Close the hood.
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Compare the two ampere readings you made a note of to the ampere range you noted in the owner's manual. The first reading you noted is lower than the second reading as you turned on the electrical equipment in the car. Your readings will be the same, or within 10 percent, as the readings from the owner's manual if your alternator is working properly. For example, if the range in the manual is 50 to 75 amperes, then your lower reading should not be less than 45 amperes and the higher reading should not be less than about 65 amperes. If they are, get the alternator checked out professionally.
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Tips & Warnings
Before you start, put on a pair of protective rubber gloves so your hands don't get covered in grease and then open your car's hood.
References
- Photo Credit New car petrol engines image by Christopher Dodge from Fotolia.com
