How To Test Alternator of Your Truck For Issues

Knowing if your alternator is in good working condition is difficult when you do not know how to determine its health. You can test the health of your alternator using a voltmeter. But you can also try other methods depending on how well you understand your truck. The latest trucks have a computerized charging system which will require different approaches to test for alternators. Shared in this guide is how to test alternator in your truck for issues and know what to do after that.

What you should Know

When using a voltmeter, your engine should rev up to 2000RPM, leaving it running as you test the battery.

A good alternator gives a voltage of between 12.2V to 14.5V, but when the readings on the voltmeter reduce, or it does not make any motion, your alternator is faulty.  

If you are unsure how to test your alternator’s health, take your truck to any auto shop to check the health of your alternator.

Testing the Health of Your Alternator Using a Voltmeter

Consider the following steps to determine the health of your alternator with a voltameter.

Source a Voltmeter

You can ask a friend or buy one if you do not have one. It costs less than $20. Alternatively, you can use a multimeter that measures the voltage and other electrical properties like current resistance. 

Check the battery of your Truck.

For your truck to start, you will need the battery. It is the battery that, in turn, provides the energy necessary to turn the alternator. As the alternator turns, it generates electrical power for your truck’s electric parts, including charging the battery. When your battery is low, you will ot be able to ignite your engine and check the health of your alternator. Consider doing the following to check your battery.

  • Before attaching the voltmeter, turn off your engine.
  • Open the hood or access your battery where it is. 
  • Attach the voltmeter to the terminals of your battery. 
  • Monitor the readings of the voltmeter. If it is 12.2volts and above, then your battery is healthy. 

Start Your Truck and Rev the Engine to 2000RPM

Starting your truck and revving the engine to 2000RPM will draw power from your battery to the alternator. Your engine should be running as you test the alternator. This time, the readings in your alternator should be between 13 and 14.5 volts. Such readings will show that your alternator is in good health. Your alternator is faulty if your voltage doesn’t make any motion or reads figures less than 12 volts.

Turn on the lights, radio, wipers, AC, and all other parts which use electricity in your truck. The voltmeter readings should be above 13 volts to indicate that your alternator is in good condition with other electrical components running.

Monitor Your Alternator

Monitor your alternator gauge while all other electric parts are running, be keen to note if your alternator is straining. If not, it is in good health.


If your alternator is dead, consider buying and installing a new one. You must walk to the nearest shop or make an online order. But it is necessary to buy an alternator from a shop so that they test it in your presence.

How An Alternator Works in a Truck

Many people know the battery offers power to the windshield wipers, headlights, or even radio. But is that really the case? The power from the battery is necessary only when you start your truck and when the engine is off. It is the alternator that does all this. In this guide, we will go through the steps to learn how an alternator works in a truck.

What is an Alternator?

Alternator performs the role of converting mechanical energy into AC electrical energy. The alternator works similarly to the generator. The slight difference is that a generator converts mechanical energy into either AC or DC electrical energy. The converted energy powers other parts of the truck, such as the wipers, headlights, and even charging the battery.

Components of an Alternator

The components of an alternator give your truck the correct amount of power. Let us look at the parts of an alternator and what they do.

Rotor and Stator

Inside the stator is a rotor surrounded by a magnet with conductive copper wiring. The rotor and stator generate electricity by moving the magnet over the wiring. The two are the main components that produce power in a vehicle.

Voltage Regulator

From the names, it oversees the power the alternator makes and delivers to your truck and the battery.

Diode Rectifier

Converts the power from the alternator into a form that the battery can use and store.

Cooling Fan

Cools the alternator, which produces a lot of heat when functioning. It has rotating fun and aluminum casing that dispenses heat from it to the surrounding. 

How an Alternator Works

An alternator does the work of producing electricity and charging the battery of your truck. How an alternator performs, the above two roles will let us know how it works.

How an Alternator Generates Electricity

The engine is the primary source of electricity. An alternator has mounting types. In old engines, a pulley moves from the crankshaft to the alternator. In new engines, the alternator has a serpentine belt that connects it to the crankshaft. The mechanical energy resulting from the belt movement is what spins the rotor at a very high speed. 

The spinning of the rotor produces electricity. The magnets create a magnetic field as they pass over the copper wiring in the stator. The magnetic field generates the voltage which the stator captures. The power from the stator goes to the voltage regulator, which transfers it to other parts of the truck. 

How An Alternator Charges a Truck’s Battery

The electricity flows in different ways, but the battery only receives current in one way or direct current. The current intended-to-go battery first moves to the diode, which converts to DC before moving to the voltage regulator. The alternators generate the alternating current, which can flow reverse. After the conversion, the current charges the battery or gets stored. 


The alternator does the primary role of converting mechanical energy into electric energy. It gets the mechanical energy from the engine as it functions. Upon successful conversion, the electric energy will help power your radio and wipers and charge your battery. The alternator has parts which does the energy conversion.