{"id":1974,"date":"2019-07-02T06:25:54","date_gmt":"2019-07-02T13:25:54","guid":{"rendered":"https:\/\/www.emanualonline.com\/blog\/?p=1974"},"modified":"2025-04-10T08:39:06","modified_gmt":"2025-04-10T13:39:06","slug":"how-to-correctly-test-an-alternator","status":"publish","type":"post","link":"https:\/\/www.emanualonline.com\/blog\/how-to-correctly-test-an-alternator","title":{"rendered":"How To Correctly Test An Alternator"},"content":{"rendered":"

A faulty alternator is a common cause of engine<\/a> problems and often requires expensive work to be done by a certified mechanic. If you’re looking to save on your alternator repairs, troubleshooting the problem yourself may be a good idea. Such a task can be performed by almost everyone once you have mastered some basic electrical troubleshooting<\/strong><\/a> notions. Read on to learn everything you need to know to test your car\u2019s alternator, how to replace it, and save a lot of money along the way.<\/p>\n

\"Automotive<\/p>\n

How Alternators Work<\/h2>\n

A vehicle\u2019s alternator is the main component of the charging system. While the battery is exclusively used to start the engine, the alternator\u2019s job is to take the relay once the vehicle is running and recharge the battery.<\/p>\n

When you turn the ignition key and start your engine, the starter drains a significant amount of the power stored in the battery. By itself, the battery could not make the car run for longer than 10-15 minutes. The alternator creates electricity to power every electrical system on your car and sends the excess to be stored inside the battery for future use. That way, the battery stays fully charged at all times and is always ready to start your car once again the next morning.<\/p>\n

The alternator can be compared to a dynamo in the sense that it transforms kinetic energy into electrical power. This is made possible by a simple magnet rotating inside a copper coil. In motion, the magnet displaces the electrons on the copper atoms thanks to its magnetic field<\/strong><\/a>. This operation is ensured by the alternator belt, which transmits the power of the engine, which is why the alternator only fulfills this function when the engine is on. The electrons rotating in circles create electricity that will then be transferred to the battery.<\/p>\n

Main Components<\/h2>\n

Rotor<\/h3>\n

The rotor is the rotating part generating a magnetic field via an excitation coil fed by brushes. It is composed of two shells nested, one inside the other, forming an assembly of three electromagnets. The rotor is connected to the crankshaft via the drive belt and constantly turns at the same speed as the engine.<\/p>\n

Brushes<\/h3>\n

Charcoal brushes are used to feed the electromagnet with power while it turns on itself. A standard connector is not enough as the wire would basically wrap on itself as the rotor turns. Exactly as with starters and steering wheels, a connection allowing contact between two rotating parts is needed, and this is where the brushes come into action.<\/p>\n

Stator<\/h3>\n

The stator, as the name suggests, is the static part of the alternator. In the case of a three-phase alternator, the stator is composed of three coils. Thanks to the magnetic force induced by the magnet of the rotor, electrons move and generate alternating current in each of the coils.<\/p>\n

Voltage Regulator<\/h3>\n

Modern alternators have an electromagnet in their center. The PCM can modulate the intensity of the magnet using a voltage regulator, making it possible to control the amount of power produced by the alternator.<\/p>\n

Diode Assembly<\/h3>\n

Since a three-phase alternator generates an AC current and cars only run on DC current, the power needs to be rectified before being sent back into the system. To do this, manufacturers use a diode assembly. Diodes only allow current to go in one direction. Connecting them in series will then redirect the current produced by each coil to ultimately convert the AC input into a DC output.<\/p>\n

\"Cutout<\/p>\n

What Happens in the Case of an Alternator Failure<\/h2>\n

Whenever your alternator starts misbehaving or stops working completely, the first thing you\u2019ll notice is the charging system warning light lighting up in the dashboard. This warning light is there to let you know that the power in the system is slowly dropping and is now under a normal threshold.<\/p>\n

The battery warning light is usually shown whenever the voltage reading of your electrical system goes under 12.6v. When the alternator stops producing current, the battery will take the relay and power everything in its place. As said earlier, the battery itself won\u2019t be able to power the car for long, though. If the condition remains the same, the engine will shortly die.<\/p>\n

In such a situation, turn off all the electrical accessories to save as much power as you can and quickly find a safe place to stop the car. Turn off the radio, the headlights, the climate control, the navigation, and the entertainment system to be able to go as far as you can before it dies and save on tow truck fees.<\/p>\n

Most Common Causes of Alternator Failures<\/h2>\n

Broken Drive Belt<\/h3>\n

The drive belt is what\u2019s making the rotor spin. If the drive belt breaks, the alternator will stop turning and producing current altogether. In the case of an alternator failure, always begin by inspecting the belt and making sure it\u2019s not too loose or damaged.<\/p>\n

If the belt is completely torn up, the drive pulley might be stuck and will need to be replaced.<\/p>\n

Worn Out Internal Components<\/h3>\n

Any worn-out component can cause the alternator to stop working. Charcoal brushes, for example, are often prone to premature wear due to the constant friction of the rotor. Water and rust can also cause an open circuit or short-to-ground condition to the rotor and stator.<\/p>\n

In any case, buying an alternator rebuilding kit instead of replacing the whole thing might be a good solution.<\/p>\n

How to Test an Alternator Using A Multimeter<\/h2>\n

\"Auto<\/p>\n

Before starting to troubleshoot an electrical problem, make sure you get yourself a good multimeter<\/a>. Try to buy one equipped with an amp clamp. This feature really helps to speed up the process of measuring amps which is, otherwise, kinda complicated.<\/p>\n

Check the Battery Voltage<\/h3>\n

First, check the battery voltage while the engine is turned off. This will give you a reference value to compare with the alternator output voltage. Connect the device to the battery terminals: the red wire of the multimeter must be connected to the red terminal of the battery, and the black wire directly to the black terminal. The voltage reading should be around 12.6v. If it\u2019s not, you\u2019ll have to charge your battery with a smart battery charger first, or you might end up with false readings.<\/p>\n

Measure the Voltage of the Alternator<\/h3>\n

Start the engine and read the battery voltage again. The voltage should now be between 13.3v and 14.6V<\/p>\n