Editing Troubleshooting alternators

The function of an alternator is to keep the battery(s) in your vehicle charged. In order to troubleshoot the functionality of the alternator you will need some basic electrical tools. A good digital Volt/OHM meter is the bare minimum. When the vehicle is running with a fully charged battery you should read between 13.6 and 14.2 volts at the battery. This is the basic test to see if an alternator is working at all. Before performing the above test make sure the alternator drive belt is tight. If the voltage is within spec the next this to test is to see how much current it is capable of delivering. Most alternators will have the rated current capacity stamped on the case somewhere. 

To test current you will need a high power amp meter capable of 100 amps dc. Most home mechanics will not have this in their tool box. You will need to either take it to a shop that can test it on the car, or pull it and take it to one of the auto parts stores that has a machine to test it.
If it tests good off the car but does not work on the car it is time to check the wiring to the alternator. Alternators all work basically the same. Usually there is a wire to excite the alternator into working and a sense wire to tell the alternator what the voltage is currently in the system. To properly troubleshoot this you will need a wiring diagram for the vehicle that pertains to the alternator wiring. Most times these can be found on line for the common alternators.

If you find that the voltage is not within spec, usually this will show up as 12 volts or less at the battery, you can purchase a rebuild kit for around $20 to $25 bucks that has most of the common failure parts included. Most are fairly easy  to rebuild and at a fraction of the price to purchase a new or rebuilt.

A good source of information on the topic of alternators and automotive electrical systems is [http://www.madelectrical.com  Mad Electrical] 

[[Category:Electrical]]
[[Category:Troubleshooting]]