One brush broken off of voltage regulator - is the regulator doing anything? - PeachParts Mercedes-Benz Forum

chetwesley · #1 09-12-2012, 10:08 PM

Without it?

I have an alternator that seems to be chewing through voltage regulators. I think it is a warn/warped rotor or something, but it has broken three of them now in the same fashion, and now it is seemingly occurring more quickly.

I have a new alternator, but can't install it until Friday. Is the alternator doing anything without the missing brush?

It doesn't seem that the battery is discharging at a high rate. I drove 50 miles with the lights on and the battery was not dead. What do the two brushes do?

jay_bob · #2 09-12-2012, 10:56 PM

Alternator operation 101, this is what I do at work...
The outer shell of the alternator contains 3 coils of wire wound 120 degrees apart. It creates three phase electricity just like the big ones at the power company. Instead of passing the electricity out as three phase, a bank of diodes rectifies the three phase ac into dc. This winding is called the armature winding.

The inner part that rotates has a single coil of wire wound on it. The voltage regulator takes dc voltage from the battery, through the charge light, and uses the dc voltage to energize the rotating winding. This winding is called the field winding. The dc current in the rotating winding causes it to become a magnet. The rotating magnetic field induces current in the armature windings. This excitiation current goes through the brushes on the back of the regulator pack into the rotating field winding.

The regulator varies the amount of current sent through the field coil. By doing this it is able to control the output voltage of the armature windings. If no current goes through the field coil then no electricity is produced in the armature windings.

So if your brush is totally broken off then there is no way for the alternator to be producing electricity. I suspect you are living on borrowed time because the battery in these Diesel cars is so huge to allow cold morning starts that in warm weather you can get away with running the car for several days.

The reason you are eating brushes is that the rotating contact piece on the field assembly, that the brushes contact, called the commutator, is damaged.

In the mean time, if you have access to a battery charger, I would use it to keep the battery from being deep discharged until you can replace the alternator.

Jeremy5848 · #3 09-12-2012, 10:59 PM

The brushes feed current to the rotor, which generates a magnetic field, which spins as the rotor revolves, driven by the fanbelt. The rotating magnetic field "lines of force" are cut by the windings (wires) in the stator, generating electricity in the windings. This electricity is AC; it is rectified by a set of diodes in the alternator and, as DC, is sent to the battery and the various loads in the car. The regulator watches the voltage coming out of the alternator and, when it is high enough, cuts back on the current to the rotor.

With only one brush there is no current through the rotor and no magnetic field except for a small amount of magnetism in the metal of the rotor. Thus hobbled, the alternator cannot produce but a tiny amount of electricity and you are mostly running on your battery.

Jeremy

scottmcphee · #4 09-13-2012, 09:41 AM

When I replaced these brushes I could check the commutator through that hole and decided to clean it with very fine grit sandpaper (not emery), solvent, and a clean wipe. All surgically done with a finger through the hole. Fingertips are very sensitive to rough edges.. you will feel a chip or burr on any commutator pad that is bad. Rotate the alternator with a tool on its pully, engine not running.. (obviously?) to do this kind of thing!

Codifex Maximus · #5 09-15-2012, 04:32 AM

I wholeheartedly agree with JayBob and Jeremy regarding the way an alternator works. However, I'm not so sure I'd be sticking my fleshy finger into an alternator like ScottMcPhee does.

Might be sharp in there!

Anyway, could be new alternator time.

layback40 · #6 09-15-2012, 05:11 AM

Quote:

Originally Posted by scottmcphee

When I replaced these brushes I could check the commutator through that hole and decided to clean it with very fine grit sandpaper (not emery), solvent, and a clean wipe. All surgically done with a finger through the hole. Fingertips are very sensitive to rough edges.. you will feel a chip or burr on any commutator pad that is bad. Rotate the alternator with a tool on its pully, engine not running.. (obviously?) to do this kind of thing!

Commutators are for DC generators. Alternators have slip rings.
If the same brush is breaking each time, chances are you have damage on the slip ring. I hope you are not forcing the reg in, trying to force the reg into place when the brushes are not sitting properly on the slip rings will break the brushes.

jay_bob · #7 09-15-2012, 06:16 AM

Quote:

Originally Posted by layback40

Commutators are for DC generators. Alternators have slip rings.

You are correct, I had motor on the brain when I wrote that.

layback40 · #8 09-15-2012, 06:59 AM

Quote:

Originally Posted by jay_bob

You are correct, I had motor on the brain when I wrote that.

Hey Jay,
Dont be concerned, every one knew what you were talking about & others followed you !!
I just wanted to get to correct it before John or Roy did !

JHZR2 · #9 09-15-2012, 10:46 PM

BTDT:

One connected, one not. No charging. Had to drive home 165 miles, half in the dark, on just the charge in the battery. Minimized headlight use and everything. Car ran fine, but was a bit worried about brake lights on busy roads at the end...