fbodfreek

What does this thing do? I think my alternator is shot (putting out around 10 volts), but while shopping for one on the internet, I ran across this and it's significantly cheaper than the alternator. What does it do?

Stuart Moss

A regulator, well, regulates the alternators output voltage. It is only a small electronic device about 1" x 2" x 0.25" that is usually mounted inside an alternator, and it's primary job is to try to maintain a constant output voltage typically between 13.8 - 14.8 volts depending upon ambient temperature.

They are not expensive. I do not know exactly how much, but would guess ~$20 or so.

Grand Prix

To elaborate, the rectified alternator output can go as high as about 60V unloaded. It varies depending on how hot the alternator is, how much load is on it, and how fast its spinning. You would go insane trying to make a car work with voltages that ranged from 12V to 60V. The voltage regulator takes in this widely varying voltage and puts out a nice constant voltage. The output voltage depends a little on who made the regulator and so forth, but its generally around 14.4V. Now you have a nice 14-14.5V output from your alternator having little to do with how fast its spinning or the load. If you are only putting out 10V it could be the regulator but more likely its a diode failed. Usually when a regulator blows the voltage goes high.

Generally I don't repair alternators, I just replace them. Reason being is the bearings wear, the coating on the windings tends to break down with age, and other parts could have stressed when the alternator failed. Not to mention you get a warranty so if it fails a week later you get a whole new one. If you still want to give it a shot replace the diodes and regulator both at the same time. What year is the car? I may be able to dig up some diagnostic information for ohm-meter type checks to try to isolate a failed part.

Stuart Moss

That was good Grand Prix. But I have a feeling that Mr. fbodfreek does not know what an ohmmeter is let alone how to use one to make further checks (based only upon his question).

However, in the event he does, it's a simple matter to check the rectifier to at least make one check for a common diode failure if you want to fix it yourself (it's fun, at least to me).

There are six diodes in the rectifier. All you have to do is check (preferably with an ohmmeter making sure it's on the "diode check" function if it's a DMM) these six diodes. I believe you can do this from the rear of the alternator without removing the rear case.

If you find a bad diode(s) here, I'd just replace the rectifier before monkeying with the rectifier (which may or may not be bad too, but often it's the rectifier that goes first).

CS130 alternators are notorious for failing due to overheating, destroying the rectifier. This happened to me once and got an "Iceburg" modification kit to help it operate a little cooler.

Hummer

Just buy a repair kit. It comes with the bearings, voltage regulator, diode trio, brushes, maybe more and is only about $20Cnd, which is probably $2.50US. Easiest repair I've done under the hood-all self explanatory.

fbodfreek

Thanks guys, I just replaced the alternator with one that's got a lifetime warranty. The old one all of the sudden was only putting out 8-10 volts (yes I've got a tester and I do know what an ohm is) Problem Fixed. Thanks for the input.