I'm pretty sure that my alternator is dead after breaking down on the motorway (in road works with no hard shoulder and three lanes of traffic - not fun).

New ones seem stupidly expensive, so I'm planning to get one off ebay, or from a breakers, unless anyone knows of anywhere good for new or reconditioned alternators??

Would be good if someone could confirm if my conclusion is correct as well....

When running, a voltmeter across the battery shows the voltage dropping from 11v and continuing to drop constantly.

Volt meter from the -ve on the altenator to +ve on battery shows something less that 10v which constantly changes.

Volt meter on -ve on alternator and grounded on the car with the ignition on, but the engine not running shows a fluctuating voltage from 3v to 11v.

Does this mean that maybe it's just the regulator part of the alternator that has gone? Is it worth having a poke around to see if it can be repaired?

I once had an alternator reconditioned, I drove to work in the morning, took off the alternator and dropped it in, then picked it up in the evening fitted it and drove home.
Grendel

I fitted a new alternator and a new battery to the car, and all is good. It works, which is nice.

However, this morning noticed that the battery light is glowing dimly, so investigated what was going on.

The battery voltage remains at around 15v, with the alternator giving out about 19v. Everything works properly (apart from the fuel gauge), so I'm confused.

Is this something I should just ignore, or is there some earth connection or something that needs to be checked?

could be the earth from the dashboard, I have no idea where that is though
Grendel

Hadn't thought of that. I'll have a poke around tomorrow and see what I can find.

Well, it died again. The battery light came on, and it died and wouldn't start. The breakdown guy suggested the new alternator was faulty, so I swapped it out for another one.

And, the same still happens. Jump start the car. All works, the battery charge light comes on and gets brighter, drive a couple of hundred yards and it looses all power and dies.

The battery is fine, the alternator is working and outputting the required power etc... so what could it be?

Are there some hidden in-line fuses or something, as it seems almost as if the laternator is providing no charge at all to the battery, even though it is working!

I discovered after poking around that there was a fuse between the alternator and the battery.

It's an 80amp MEGA fuse!! And it had blown. I guess the regulator on my old alternator went out in spectacular fashion, and had that fuse not been there my battery would have turned into a firework.

Managed to get hold of the correct fuse, and all is now good!