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A Guide to Alternator Troubleshooting

Suketu Mehta
A car alternator is like a mini generator which charges the car battery. Read and learn about its common problems, and solutions for the same.
The alternator is a small but important component of any car's electrical system.
A car engine functions with the help of air, spark, and fuel. Electricity, necessary to generate the spark, is supplied by the battery in small amounts. However, since it is not a large amount, the alternator steps in to ensure that the battery is constantly charged, and the car keeps running.
The alternator constantly gives an output of 13.5 to 14.8 volts, as the car battery is 12 volts and needs constant charging. Magnets inside it spin around copper wires continuously at a high speed, generating electricity.
The current is converted from AC to DC for the battery to use. In case additional voltage is produced, the voltage regulator shuts down the flow to prevent the car battery from overcharging.

Solving Alternator Problems

The entire system comprises the alternator, ignition switch, distribution wiring, a battery selector switch, the regulator, and batteries. There could be a malfunction in any of these parts, requiring some professional repair.

Battery Selector Switch

Mostly used in older batteries, battery banks are charged with help of a selector switch which facilitates charging.
As a working alternator contains energy stored in its field winding, disconnecting the batteries cuts off the alternator output and numerous volts reach the output. As the same circuit is supplying current to other devices, this sudden surge of high voltage can destroy any of the other equipment.

Distribution Wiring

The wires or cables connected to the alternator carry large amounts of current, and are stiff and under vibration most of the time. This can lead to loosening of the nut at the output stud. You should, hence, ensure that the wires are properly connected to the alternator and battery.

Ignition Switch

A sign of an ignition switch malfunction could be the system's inability to charge. You should ensure that the alternator regulator is getting voltage supply when the switch is on, and none when it is switched off.


A regulator is constantly under stress, as it has to deal with high currents and changing transients. Look for a terminal with a wire connecting to the alternator. Use a voltmeter to check the current. There should be no or minimal current when the ignition switch is off, and when it's on, the voltmeter should depict several volts.

How to Troubleshoot an Alternator Problem?

Step 1

To start the troubleshooting process, take out the car battery. Loosen the nut on the clamp with a wrench, and remove the negative cable before touching the positive one. Pull the car battery out from the engine bay.

Step 2

Connect the positive lead of the battery charger to the positive battery terminal. After this, connect the negative lead of the battery charger to the negative battery terminal. Switch on the battery charger.

Step 3

As soon as you notice the 'full charge' sign on the battery, unplug it from the charger. Leave the battery as it is for about 12-14 hours. Switch the dial on the voltmeter to 'voltage'.

Step 4

Take the red lead of the voltmeter, and touch it to the battery's positive terminal. After this, touch the black lead of the voltmeter to a metal piece which is grounded (earthing). Remember not to touch the black lead to the negative battery terminal.

Step 5

On a piece of paper, take down readings of the charge as shown by the voltmeter. For a standard car battery (12 volts), the reading should come close to 14. In case your car battery voltage shows a reading below 13, it indicates that the battery is dead, and won't bear any charge. If the battery does bear a charge, it means your car alternator is defective.

Step 6

Check the following:
  • The wiring should not be frayed.
  • The electrical plug should be tightly fit into the alternator.
  • The grounding wire should be rust and paint free.
  • There should be no loose wire connectors or grounds, as it causes overheating.
  • No noise should come from the alternator. In case you hear some, the bearings need to be changed.
After trying out the instructions given, if you notice that the damage is severe, replacing the alternator is a good option, especially if the car is really old, to avoid any further problems.