How To Diagnose Alternator Problems - Car Talk

How to Diagnose Alternator Problems

This post is all about how we can test the car alternator to see if it’s faulty or not. Many a time you see people change their alternators without carrying out proper tests on the alternator to see if it’s actually the cause of the problem. After changing it they find out whatever is the problem still persists. For the simple reason that the car battery is not being charged does not mean that the alternator is faulty. Before you pass judgment on the alternator, take some steps to be sure that the alternator is dead.

Check the Battery Terminals & cables – Anytime you work on car electrical systems, it’s always good to start with the battery. Do some basic checks on the battery first. The first thing to check on the battery is the terminal connections. You need to make sure that the connections are tight and clean with no corrosions on the terminals. So many electrical problems originate from poor connections at the terminals. Corrosions that build up over time can create a resistance between the battery terminal and the cables thereby compromising the performance of the battery and also the alternator. So check that the battery terminals are well connected and also check for any signs of corrosion.

Test the Battery – The next step is to test the battery with a voltmeter. This is a very simple process. Set the voltmeter to a range above the battery voltage. For instance, car batteries are usually 12v; you need to set the voltmeter to something above that (say 20v). Then connect the positive probe of the voltmeter to the negative terminal of the battery and note the reading on the voltmeter. A reading of 12v and above is a good reading but if it is above 12.6v then the battery is probably overcharged and the surface charge may need to be removed either by turning on the headlamps for some time.

Check the Alternator Output, Cables & Belt – Leave the voltmeter still connected at the battery terminals, start the engine and rev it or raise the engine a little for some time while checking the reading on the voltmeter at the same time. The reading should be well above battery voltage but not more than 15.5v. Any value more than 15.5v indicates that the system is probably overcharged. Overcharging condition is just as bad as undercharging condition. Though some alternator systems might run more than that value but most cars still maintain a reading less than 15.5v. Now if you turn up the engine and the reading is less than the battery voltage then it’s possible the alternator may not be doing its work. However, don’t condemn the alternator yet we still have a few more things to check. Check the alternator cables and wiring, especially the wires that connects to the voltage regulator, for any kind of damage. Another thing to check is the alternator belt. If the belt tension is not sufficient enough to spin the alternator, the alternator cannot produce adequate electricity. So make sure the alternator belt is tight and secure.

Voltage Drop Test – Perform a voltage drop test by loading the system. How to perform a voltage drop test was treated in our earlier post. Click here to read it.

What if we still get an unfavorable reading after the tests?

There are two types of voltage regulators – external and internal voltage regulators. The external voltage regulator is separate from the alternator assembly while the internal voltage regulator is part of the alternator assembly. So, if the voltage reading falls below the battery voltage, replace the voltage regulator if it is an external regulator. If the regulator is internal then you just have to replace the alternator. Again, in most modern cars, voltage regulation is controlled by the ECU. It just might be that the ECU is not sending the right command to the alternator to push out the required voltage. Just keep that in mind.

So this post is basically to make sure that when you remove the alternator for replacement that you are sure to a greater extent that the alternator is the problem and not something else.

We hope this is very informative. Thanks for reading.

Source: http://carblognaija.com/how-to-diagnose-alternator-problems/