View Full Version : Generator failure?

08-03-2012, 06:11 PM
What are the signs of a failing generator?

08-03-2012, 06:50 PM
Not charging the battery.

Loud screeching noises coming out of it.

Inability to keep its smoke inside its housing...

Seriously, whenever you suspect a generator problem, you should consider the possibility that the regulator may be the problem. Often it is.

Beyond that, there are checks you can make to determine where the problem is.

What are you experiencing that motivated the question?

08-03-2012, 07:52 PM

Just some hints that something may be wrong.

(1) Relatively new battery (2 years old) suddenly seems to be weakening -- starter beginning to hesitate. (I'm having the battery checked tomorrow.)

(2) Unusual slight burning smell has appeared. (Although this may be a gas leak from carbs that I have now fixed).

(3) Ignition light comes on bright when I slow down to stop and when I am stopped (idling).

I've had trouble with new regulators in the past. Had to replace the one that came with the car three times before we found one that worked. The one in the car now is only 2 years old (though age certainly is no guarantee) and it was pre-adjusted by Moss.

Geo Hahn
08-03-2012, 08:16 PM
Every generator failure I have had has been a mechanical failure (bearing, brushes, bracket). All pretty easy to diagnose and fix. The Lucas trouble-shooting manual (and to a lesser extent Bentley or Haynes) have procedures for checking all aspects of the generator/control box system.

For a start, you could see what voltage the battery is getting when the engine is at 2000 RPM or so. I usually set it for about 13.4VDC. Much higher gets the water percolating, much lower doesn't keep up with the draw.

08-03-2012, 08:40 PM
Hi, George,

Thanks. How and/or where do you measure the VDC of the generator? I've never worked on a generator before because mine is only two years old.

08-03-2012, 09:28 PM
In theory, you can take it from anywhere in the system with a connection. I would check at the battery terminals...as that is showing how much charge is actually reaching the battery, and that's what you are interested in. A charged battery at rest (no draw) should show in the neighborhood of 12.6 volts. Once the gen kicks in, it should go between 13.5 and 14.4...again, roughly. Higher is definitely a regulator adjustment. Lower could be reg or gen.


08-04-2012, 07:35 AM
Thanks, John

08-04-2012, 08:19 AM
If I had to bet, I'd put my money on the regulator. USUALLY a generator either works or it doesn't; the kind of problem you describe sounds to me like the contacts in the regulator relay are getting burned or just worn out. You can burnish them with a bit of paper or thin cardboard between the contacts, or you can get a special file for doing that. Check the adjustment, too, of course.

A lot of the new components from the usual suppliers are not good quality. It might help to get an original, Lucas one, even if it's used, and see if that has a better lifetime.

Oh, yeah, be sure to disconnect the battery when you work on the regulator, or anything in the charging system, for that matter.