How To Tell What Amp Your Alternator Is?

A common point of failure in today’s vehicles is the alternator.  What is essentially a electrical generator, the alternator converts mechanical energy to electrical energy to power our vehicles.  If you’ve experienced an alternator failure in the past, we’re here to help you diagnose the problem.

The best place to begin to evaluate potential alternator problems, is to determine your baseline and know how many amps your alternator is currently generating.  There are a few methods to measure alternator output.  We’ll cover a few of these options to better prepare you to move forward with repairs or replacements.

How To Tell What Amp Your Alternator Is?

How To Tell What Amp Your Alternator Is?

Understand what you’ve got

First, you need to know what you’re working with before you even begin to consider whether or not you’re over-taxing your alternator.

You need to know what amperage your alternator is rated for.  You will need to locate the stamp and/or the placard on the alternator that shows the part number and the amperage.  If the amperage isn’t easily legible, the part number can tell you what you’re looking at.  It’s a simple google search to find what you need to know.

If this still doesn’t lead you to the correct information, you can likely use a website such as AutoZone.com to enter your vehicle’s information and find out what alternators are recommended for your vehicle.  This only helps if you or a previous owner haven’t installed an aftermarket alternator.

Getting what you need for determine the amperage provided by your alternator

Now that you know what you should expect to see in terms of rated amperage, you can test your alternator to determine if you’re receiving an acceptable amperage.

To start with, you should ensure the belt connected to the alternator isn’t slipping on the pulley.  Prior to starting the engine, check the tension of the belt by pulling on it slightly.  If you can manually cause it to slip, you need to replace the serpentine belt.  You can sometimes see and/or hear the belt slipping after starting the engine and taking a look at it.  Obviously, don’t try to pull on it at this point.

The easiest way to test your alternator is to use a voltmeter or multimeter, which can be picked up in a local hardware store or online at a multitude of places.  Ensure the multimeter is set to read DC Voltage (VDC).

The next step is easier with a helper.  You’ll be testing your battery voltage while the vehicle is running.  Ideally, you should have somebody increase the RPM’s to between 1500 and 2000.  Testing the battery using the multimeter, you should see a voltage range of between 13 and 15 volts.  If the voltage fluctuates a great deal, or drops below 13 volts, then your battery isn’t receiving enough of a charge from the alternator.

If the voltage is dropping and you already determined the serpentine belt appears to be in good shape, you need to ensure the wiring harness for the alternator isn’t frayed or damaged in any way.  This would also be a good time to check on any related fuses that could be contributing to the problem.

If none of the above suggestions correct the alternator issue, then it’s time to replace your alternator.

Find label code and ask your dealer service

Another way from Jack in comment, thank for his help 🙂

There should be a label with codes (numbers and letters) in the trunk hood or glove compartment, or somewhere else. Call the dealer and ask what code to look for, or give the dealer service person the VIN number, then the dealer service person can tell what size amp alternator was installed at the factory..

Easy Mode

If you don’t want to spring for a voltmeter or multimeter to do a little testing on your own, there are a number of auto parts stores that will do the testing for you free of charge.  This is assuming your vehicle is in good enough shape to get you there for the test.

The verdict

Hopefully we’ve been able to shed some light on the subject of alternator functionality for you readers.  It might not always work out cheaper, but having the knowledge of how to troubleshoot problems on your own can go a long way toward better maintaining your vehicles.

Mike Cross

You have to look for teachers. If you want to be a mechanic, go hang out with mechanics.

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