Well, you're only the third person to catch that and bring up the generator / alternator issue. Most people don't know the difference. In fact, you will not find the term "alternator" in most automotive service manuals. It was first used by Chrysler in 1960 and they copyrighted the term. All other brands that developed their own starting by 1963 used the term "AC generator" and that is what the industry has gone to in an effort to standardize terminology since 1996. As an instructor, it is more important for me to use correct terminology in the classroom, but if you go into any parts store and use the word "alternator", no one is going to correct you or even know the difference. Everyone will know what you mean.
As for the diodes, yes, all voltage regulators contain hundreds of diodes, and transistors, and resistors. I'm referring to the six high-current diodes in the output circuit that are found in every AC generator. When one fails, you will lose exactly two thirds of the output capacity. The most common car alternator / AC generator is around a 90 amp unit. That means with one failed diode you will only get 30 amps on a load test. "Ripple" will also be very high due to the one missing phase and that shows up on most professional load testers. I type this same information at least once per day and I'm involved with two people right now with this same issue. It's so common and is much more noticeable today with all the insane computers on the cars that react negatively to that ripple. In the '70s you could have a bad diode and never know it. With no electric fuel pump, no computers, no electric radiator fan, and little electronics, 20 amps from a 60 amp unit was often enough to run a few lights and keep the battery charged. The same was true, I'm assuming, on a '70's tractor, but not today. You mentioned all the computer controls you have to deal with. So do we, and at least half of ours are unnecessary and needlessly complicate what used to be reliable systems. It's partly because of all those silly computers that charging system problems become more evident and more common. The days are long gone when the alternator, ... Uhm, ... I mean AC generator would last the life of the car.
You misunderstood my use of the 240 amp generator story and I appreciate the chance to clarify what I meant. You got 80 amps from yours on a load test which is exactly correct and proves it is working properly. The only OTHER way to get 80 amps is if it was a 240 amp unit with one bad diode, ... But there is no such thing as a 240 amp car generator. Maybe in a tractor or an airplane or a ship, but not in a car. I probably shouldn't have even added the comment since I know it can be confusing and misunderstood.
One failed diode will not result on "stopping them all". A failed voltage regulator can. A failed stator winding can, but not just one bad diode. There's two different types of stator windings. GM and Chrysler use the "delta" winding. Even if one of them had a broken connection, you would still get one third of its rated capacity. Ford uses the "wye" winding with a brass rivet connecting one end of each of the copper windings together. Throw a little road salt and water on that and galvanic action corrodes the connection apart. That WILL completely stop the output and is often intermittent.
The voltage regulator has nothing to do with rectifying the AC output to DC. He is strictly in the input "field" circuit and only handles up to three amps, usually much less. I should add that while every AC generator must have six high-current output diodes, some have an extra pair that in effect capture a little wasted energy to bump up the output by perhaps ten percent. Doing that is silly because to design the generator for higher output only requires a few more inches of copper wire in the stator windings, and using diodes capable of handling that higher current. To add to the confusion, there are some imports that use two entirely separate, but connected, output circuits. They still have just the one field winding, but they have two totally independent stator windings, each with six diodes. Logic would dictate one failed diode would result in getting only two thirds of its rated capacity on a load test, if I did my math right, but I never actually tested one of those. Chrysler used that around the late '80s on one of their import engines but they weren't very common.
The bottom line of all this is you obviously know WAY more about charging systems and electronics than probably any other visitor to this site, and if your test methods get you correct results, there is no valid reason to try to say you're doing it wrong. Keep doing what you've had success with, but understand that the people we normally work with don't have that knowledge and trying to explain it just confuses the issue even more. In those cases they don't care to learn how something works; they just want to know what to do. That's fine for people who want to drive their car. It's not sufficient for automotive students.
Thursday, June 21st, 2012 AT 9:33 PM
