Virtually all cars built in recent years have AC generators, commonly called alternators.
The alternator electrical system represents a high achievement in obtaining the most electrical power from a minimum draw on engine output. It has been termed the ultimate electrical power source for automotive use.
The alternator offers the potential for longer battery life in addition to its primary advantage – higher output. The higher output is due to the comparatively low weight of the rotor and coil assembly allowing greater pulley ratios for higher rpm. The result, of course, is higher output – even at engine idle. Maintaining the advantage an alternate gives your electrical system is just a matter of knowing the alternator and keeping it in top tune.
The alternator is no harder to tune than the generator. If trouble is apparent, you don’t usually have to replace the entire unit. The unit breaks into two parts – the stator and rotor – allowing you to replace the one that is giving the trouble.
In many cases, you don’t even have to replace one of those major components. A common problem, low output, is normally traced to either of two things: a slipping fan belt or defective diodes (rectifiers).
Fan belt tension is critical with the alternator. Always make sure the belt is in good condition and adjusted to specification.
The one precaution you must keep in mind when working with the alternator is guarding against reserve polarity. Reserve polarity of the alternator or the battery for even an instant and you stand a chance of burning out the rectifiers. To prevent accidental grounding, furthermore, you should always use insulated tools when working in the area of the alternator.
Following adjustment of the fan belt, turn your attention to the regulator. Make sure all connections at this unit are tight. Follow this by checking the condition of the regulator points. If you find they’re burned or pitted, you’ll have to replace the regulator. Now, check and tighten all connections including those to the ignition switch, the ballast resistor, the regulator and the conducting surfaces of the fuse and holder.
Unscrew the brushes from the alternator and inspect them for wear. If worn, replace them.
In some cars, the brushes can be removed from the alternator with the unit in the car. Unscrewing the external cap screws, to which the brushes are attached, does this. In other cars, the unit must be removed from the car to reach the brushes, which can then be unscrewed.
If it becomes necessary to take the unit apart, remove it from the car and split it open, separating the stator from the rotor. Test the rectifiers first. This can be done with a commercial diode tester, although you can also use any continuity tester, such as an ohmmeter or a test lamp that plug into household current.
If a diode is defective, it must be replaced. This requires special tools and should be left to professional shop.
Next inspect the stator wiring carefully for breaks. To be absolutely sure there are none, you should test from the stator leads to the stator core with a 110-volt test lamp or other suitable tester. If the lamp lights, the stator is grounded and should be replaced.
Finally, test the field windings in the rotor part of the alternator. This is done with an ammeter hooked to the alternator battery output terminal while turning the rotor shaft by hand. The correct field current draw should be recorded on the meter. This reading differs from car to car, so check your service manual.
The above description tells you what to do if you are not getting output from the alternator. However, there are things a faultily adjusted or malfunctioning alternator can cause – most can be checked on the car.