Strange alternator behaviour

[prebordao]

A few weeks ago, the alt light started to stay on unless the engine was revved harder, say 3k rpm.
Suspected the external regulator but it "seemed" OK.
Then, a few days ago, problem disappeared with light going off normally.

Yesterday, it started again, the light only going off at about 3k.
However after a good blast on a motorway at about 150kph it started to behave again.
Question: could be the brushes on the alternator getting loose or worn ?
Anyone with a similar experience ?

[wwest]

External regulators are pretty inexpensive, even the solid state ones.

But I'd tighten/clean/burnish alll connections first.

Yes, that could well be the initial sign of worn out slip ring brushes.

[pete3799]

Impossible to trouble shoot an alt. without some voltage readings.
Suggest you hook a volt meter up and monitor it. What voltage does it read with the light off/ on?
How did you determine that the regulator was OK?

[DRACO A5OG]

I would remove it and take it and the pulley halves into a shop and have them test it on the bench tester, Most FLAPS do it for free, take it to two because sometimes the bench tester or the operator can be faulty. You need the halves so they can put a belt on it when they test, ask me how I know

You can take the whole car there to test the entire charging system but, it may not be as accurate.

I would also check your connectors at the battery just to make sure they are no dirty or in my case a hair line cracked connector.

Jim

[prebordao]

Battery connections were checked and OK.
Mechanical vr seems OK because I can see it working. Its just that when it happens the magnetic field can't pull the contact to close.
Next time it happens I'll take some readings.

[Porboynz]

I would place money on the slip ring brushes being worn out.

[prebordao]

My thought too.

1000th post !

[wwest]

Originally Posted by prebordao

Battery connections were checked and OK.
Mechanical vr seems OK because I can see it working.

with a fully charged battery the VR relay armature should be moving, vibrating, so fast it becomes more of a blur rather than a "see".

Its just that when it happens the magnetic field can't pull the contact to close.
Next time it happens I'll take some readings.

The VR relay magnetic field increases as the system voltage rises, OPENING the contacts and momentarily causing the alternator rotor's magnetic field to begin collapsing.

If you can actually "see" the VR relay armature movement then the slip ring brushes have become marginal or for some reason the alternator isn't "putting out" even with full current flow into the rotor windings.