{"id":8407,"date":"2022-04-25T07:39:19","date_gmt":"2022-04-25T07:39:19","guid":{"rendered":"https:\/\/notsealed.com\/?p=8407"},"modified":"2024-02-29T11:04:02","modified_gmt":"2024-02-29T11:04:02","slug":"4-ways-how-to-test-an-alternator-with-or-without-a-multimeter","status":"publish","type":"post","link":"https:\/\/notsealed.com\/4-ways-how-to-test-an-alternator-with-or-without-a-multimeter.html","title":{"rendered":"4 Ways How to Test an Alternator With or Without a Multimeter."},"content":{"rendered":"\n

Car alternators provide the electrical energy needed to run all of the electronics and power circuits of your vehicle. It also charges up the battery to full capacity ready for the next time your start the car.<\/p>\n\n\n\n

The car alternator is a simple device made up of heavy-duty bearings, electrical copper windings, charging circuits, diodes, and a set of carbon brushes. Over time the bearings and or brushes can wear and fail to cause the charging circuit to not work properly.<\/p>\n\n\n\n

In this post, we will go over how to test your car alternator both in the vehicle and out of the vehicle to see if it is outputting the correct voltage.<\/p>\n\n\n\n

How to test an alternator with a multimeter<\/h2>\n\n\n\n
\"How
Car battery voltage test with the engine off.<\/figcaption><\/figure>\n\n\n\n

With the vehicle turned off take your favorite multimeter and select DC voltage. Place the test probes onto the battery terminals and measure the battery voltage. It should read around 12 to 12.7 volts depending on the charge level of the battery.<\/p>\n\n\n\n

Any battery voltage below 12v then you have a discharged battery and it should either be recharged or replaced if it is over 4 years old.<\/p>\n\n\n\n

\"car<\/figure>\n\n\n\n

Once you have your base battery voltage start the vehicle and wait 30 seconds for the engine to idle smoothly. Take your multimeter and select DC voltage and measure across the battery terminals again.<\/p>\n\n\n\n

Alternator output voltage<\/h3>\n\n\n\n
\"ford
Ford Focus Alternator output voltage test.<\/figcaption><\/figure>\n\n\n\n

A good quality car alternator should output between 13.5v and 15v depending on the model and load on the alternator. Anything less than 13-volts and you will have a failed alternator. It should also be a smooth voltage and not fluctuate or jump between say 12v and 13.5 volts every few seconds.<\/p>\n\n\n\n

As you can see the alternator output voltage on a 2003 Ford Focus is 14.34 volts. This is a good voltage output from the alternator. It will temporally dip down to 12v when a high load kicks in such as the air-conditioner. An inconsistent voltage usually means the carbon brushes are failing on the alternator.<\/p>\n\n\n\n

Some smart alternators will actually lower the voltage\/current to a fully charged battery.<\/p>\n\n\n\n

Car onboard diagnostics.<\/h3>\n\n\n\n
\"Car<\/figure>\n\n\n\n

Often when the vehicle alternator is failing you will get an engine, battery, or electrical check light on the dash. The car’s onboard diagnostics is testing the output voltage of the alternator and if it dips below a pre-defined voltage then the engine battery check light will come on.<\/p>\n\n\n\n

You will need an OBD2 tester to further diagnose the problem as it could be one of 100+ general faults. I use a Bluetooth OBD2 tester for my Yamaha Motorcycles<\/a> which also works on all my cars as well. A very handy piece of hardware that is very cheap.<\/p>\n\n\n\n

How long can you drive with the alternator light on<\/h3>\n\n\n\n
\"How<\/figure>\n\n\n\n

This will be determined by a number of factors such as battery capacity size, battery charge state, and electrical load on the battery.<\/p>\n\n\n\n

To get the best mileage if your alternator has just failed turn off all non-essential electronics. This means radio, air conditioning, and driving lights if it is daylight.<\/p>\n\n\n\n

You should be able to drive around 50 miles with the alternator light on. this is with a full capacity battery. Older cars say 25 years+ old may run longer as they have fewer electronics in them such as no fuel injection.<\/p>\n\n\n\n

The battery light is on but the alternator is charging problem.<\/h3>\n\n\n\n

This could be an indication the battery is not accepting the charge. If the battery voltage drops under 12v then the battery has failed or is depleted. I like to replace my vehicle batteries after 4 years of service life as they become unreliable after this.<\/p>\n\n\n\n

If the battery light is on but the alternator is charging then the problem could still be at the alternator. If the alternator is over 190k miles old or 300,000km I would get it replaced as it is getting close to mean time before failure.<\/p>\n\n\n\n

My Toyota Highlander alternator was replaced at 200,000 miles and was still going strong but preventative maintenance is the best.<\/p>\n\n\n\n

How to test the alternator out of the car<\/h2>\n\n\n\n
\"How<\/figure>\n\n\n\n

There are a number of reasons you may need to test the alternator out of the car such as a reconditioned part, rebuilding the engine, scrapyard find, or just being curious.<\/p>\n\n\n\n

Make sure to clamp the alternator to the bench securely.<\/p>\n\n\n\n

Locate the positive terminal and clean up the bolt post with a fine bit of emery paper. Place the alternator in a vice and make sure it is clamped securely. Spin it by hand to make sure it moves freely. As the frame of the alternator is the negative ground clean up a spot to place the negative of the multimeter onto.<\/p>\n\n\n\n

\"Alternator
Alternator 4 terminal plug<\/figcaption><\/figure>\n\n\n\n

The only way to test an alternator charging correctly is to use another 12v car battery. Connect the car battery up to the alternator and get a small 12v globe and connect it to Earth and to the lamp terminal shown in the picture above. The lamp will turn off when the alternator is charging the battery. The lamp will turn on then the alternator slows down or stops.<\/p>\n\n\n\n

Now find a socket the same size as the flywheel bolt and attach it to a battery drill. On my Toyota Highlander\/Kluger 130A alternator I used a 10mm socket attached to a 1\/4 inch drive extension piece. This is what we will use to spin up the alternator fast.<\/p>\n\n\n\n

Now get someone to help you as you spin up the alternator. You should have the drill at its fastest speed to measure the voltage between the positive and negative of the housing. It should be between 13.5v and 15 volts. Make sure to use the fastest drill speed possible. <\/p>\n\n\n\n

This is one of the best ways how to bench-test an alternator off the car. The video below explains it well.<\/p>\n\n\n\n

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