Broken Alternator?

[ed2204]

Hi,

This morning, I noticed the ignition light was glowing a bit, but went out when I started driving. When I went out this evening however the light is stuck on, and will only disappear at really high revs. I've tried tightening the fan belt, but it's tight already.

I've metered the outputs of the alternator and got about 12v out of the big spade and 6v (when engine running, 0v when not) out of the little terminal.

I'm not quite sure what the problem could be, but feel that the most likely case is the alternator has given up. Is there something I might have missed? or do I need a new alternator?

Ed

[bmcecosse]

Almost certainly it just needs new brushes - if it's a Lucas 15/16/17/18/ ACR - very easy and cheap to do. I haven't done the job on later models - but I'm sure equally straightforward.

[mike.perry]

Big spade and little spade? Are you sure its an alternator and not a dynamo?

[MarkyB]

Well, they both have brushes.
Is it black, smooth with silver ends or silverish and not smooth at all?
A picture would be worth a lot of words!

[LouiseM]

If it helps, this is a dynamo:[frame][/frame]

And this is an alternator:[frame][/frame]

[beero]

12v is not enough from an alternator, should be nearer 14v, or at least more than the battery voltage when not running.

[ed2204]

it's definitely an alternator - I've replaced it with a new one now and it seems to be working well.

[bmcecosse]

Throw away society........

[ASL642]

Sometimes "speed if of the essence" If the car is a daily driver it's easier to fit another quickly to get you back on the road. The old unit can be mended/not at leisure depending on the capabilities of the owner.

[bmcecosse]

But surely everyone carries a spare alternator - or two...........?

[MarkyB]

Nope, it's only you that carries a spare engine and gearbox to ensure the good behaviour of those that are fitted .

[hanvyj]

New he has a spare! Provided he doesn't throw it away but replaces the brushes.

[MarkyB]

Indeed, however a Minor will run for ages without a charging system, I don't see the need for carrying a spare everywhere you go.

[bmcecosse]

Not for long in miserable wet weather - when wipers and lights are very necessary and the heater very desirable! I know - tried to soldier on, but was forced by rapidly failing wipers to stop and fit the spare alternator after 20 minutes or so.