Flickering generator light

[cwcarpenter98]

So on my 63, (the dummy light says generator, but the 63's were the first years for an alternator) the light started flickering very faintly this evening at idle. When I'm driving or rev the engine up, the flickering stops. It was working good yesterday.

Could it be I just need some new brushes? I haven't had any experience with alternators yet

[VetteVet]

These charging lights are designed to work when there is no path to ground for them to illuminate. When the ignition is on and the engine (gen) is not working, or if the alternator fails,the light will come on because the light has a path to ground through the voltage regulator and the alternator diodes.

Once the alternator comes on line it starts sending a positive voltage to the light by using a small portion of it's output back to the light. These two positive voltages (actually currents), cancel the path to ground for the light and the light cannot illuminate.

Normally the alternator and the battery are equalized enough in voltage to keep the light out, but when either one becomes low enough, it allows the light to come on faintly or bright depending on the strength of the resistance of the path to ground. This also occurs when the alternator undercharges or overcharges.

In your case, which is very common, at idle the alternator output is small enough to allow the battery voltage to push current through the regulator and the alternator to ground and allow the light to flicker. As soon as the alternator speed increases, it's output voltage to the light increases and the light goes out. This is also what's going on when the headlights dim at idle on the older charging systems.

What's causing this is most likely the external voltage regulator, due to it's age and weakening of the spring that closes the charging points. Most of the alternators up to the CS type will lessen their output at idle and increase as the engine revs up. You can see this if you connect a voltmeter to the out put wire of the alternator and let the engine idle and then rev it up. We don't notice it with a gauge dash but the charging light is pretty obvious in the light dashes.

It's pretty normal and the complaints about the headlights dimming is pretty universal at idle. As long as the light doesn't become bright and it goes out as soon as the engine is sped up, I don't think it will hurt anything.

There;s a few things you can due to improve the situation.
Install a smaller pulley on the alternator to increase it's RPM at all speeds.
Try a digital external regulator.
increase idle speed.
Convert to a newer CS alternator, especially if you're adding high draw items such as cooling fans.

[cwcarpenter98]

Ah, that makes a whole lot more sense now, thanks!!

I'm probably just going to run it as is until it either breaks or I end up replacing it for a higher amp alternator. I do plan on installing some AC towards the beginning of next summer, so might have to upgrade alternators there anyways