Automotive Alternators

Electricity is considered the life blood of your automobile.

This has always been the case as nearly all gasoline internal combustion engines use electricity to ignite the fuel. Today the total automobile is controlled and operated by electricity and electronic equipment. This include fuel control, emission control, accessories such as the heater and air conditioning system, steering control, brakes, lights and many more. It is obvious that the automobilecharging system that provide this power is a very important system.

Every alternator is controlled by some form of electronic regulator (in modern cars it's the onboard computer) that controls the output of the alternator. In years past that was a regulator mounted to the vehicle independent of the alternator.

It was only a few years ago and the regulator was moved into the alternator and the system was called internally regulated. A few manufactures decided that the electrical system should be interfaced with the computer network. Now most cars either control the charging system by computer or monitor it and set certain levels by using the engine control computer. Many systems reduce the alternator load during periods of hard acceleration.

How do I test & diagnose problems with my alternator?

That depends entirely on the equipment that you may have. A modern multi meter will give you a fair indication of the state of a charging system. If all that you have is a multi meter then you should measure the voltage at the battery terminals before starting the engine.

Then measure the voltage while the car engine is running at a fast idle. The so-called resting voltage should be close to 12.6 volts and the operating voltage generally ranges 13.2 to 14.2 volts at the battery.

You can also measure the output voltage at the alternator and it should measure with in 0.1 volts of the battery voltage. After measuring the voltage at a fast idle, turn on all of the accessories and the lights. The voltage should remain close to the same as at a fast idle (with in about 3 or 4 tenths of a volt).


Disconnecting a battery cable while the engine is still running will most likely damage your voltage regulator and/or the engine management computer and other components. This could end up costing you thousands of hard earn dollars.

DO NOT reverse the battery terminal when jump starting a car, truck or any motor vehicle.

Is it possible to change my own car alternator? Yes it is possible, if you have the proper tools. It's a good idea though, to read a good automobile repair manual before you try to diagnose or change your own alternator. You can find other helpful advice and information regarding automotive axle assembly.