Testing an Alternator – The Good, the Bad, and the Ugly

Most car owners will know of the frustration that comes along when there are issues with their vehicles. Knowing what the problem actually is will usually be the first obstacle as with so many moving parts in a car and its engine there are so many things that can go wrong.

One example is that of when your car battery does not seem to be charging. Many will initially think it is the battery but in reality it could also be the alternator. So many people make the mistake of going out and getting a new battery only to find out that the problem still exists.

This is why it is important to test the alternator with some alternator testing equipment before purchasing that new battery. To do this, there are a number of methods as you can see below.

The Good

The best way to test an alternator would be to take it to an automotive repair shop and have experienced mechanics put to use specialized alternator test equipment on it. Whilst this method might be the costliest of the three, it is the safest and will provide the most accurate results.

Just ensure that your automotive repair shop uses quality alternator test equipment such as those available from reputable brands. They have a variety of high quality products that are related to the testing of alternators.

The Bad

Another way is to purchase a voltmeter and use that to test the alternator. This is done by starting the engine and placing the positive probe from the voltmeter to the positive terminal on the battery and the negative probe likewise to the negative terminal.

You should now get a reading that will be around the 14 volts mark if the alternator is working, if it is more than 15, there is a good chance that the alternator is not working as it should be.
While this method works and is accurate enough, it can be a dangerous process for those that do not know too much about what they are doing and cars in general. The engine is running while you are in the hood of the car, so there is potential for a lot to go wrong.

The Ugly

The ugly way to test an alternator is the old style method that should be avoided completely. It involves starting the car and disconnecting one of its battery terminals in order to see if the car continues running. While this method certainly works, it should not be done as a number of things could go wrong that are dangerous. Firstly, the battery could blow up if a spark occurs near it and more modern cars could see their computer components fried due to a possible voltage surge going through them.

It is highly recommended that you stick to one of the other two methods.