Alternator not charging

[Paul V]

The alternator isn’t charging on the mini, its a 1996 1.3i, I’ve tried changing it but still no charge, the 2 main wires show battery voltage and the small wire about 0.4v.

Any idea what could be causing it?

[jmorgan]

I had this once on an older car and it was the ignition lamp blown on the dash. Tells the alternator to start charging, was an old system though.....

[Paul V]

The ignition light does come on but goes out once started!

It's got me puzzled, I think it might end up in a garage but I’m trying to sell it and don't really want to spend anymore money on it!

[kevinday]

Duff output regulator or maybe duff brushes?

[Paul V]

I'm pretty sure the one I've replaced it with would be ok though as it was working on the other car.

[jv_as]

Once the engine is running do all the ancillaries work at their full potential e.g. do the head lights work correctly when the engine is running, and it is the battery thats not charging. Could be many things try looking at the battery connections especially the earth, it could also be a very old battery. You need to give us more information if you would like us to fix this over the internet.

[Paul V]

Sorry the alternator isn't charging, it's only showing about 11.5v at the back of the alternator on the 2 large gauge wires and nothing on the smaller wire, I think that may be the problem as when I tested a friend’s mini all 3 were showing 14+v.

It's weird as everything started working last night, it was charging etc but now it's stopped again.

[smeagol]

IMHO this suggests a faulty alternator. I would take it back and get them to check it for you. The intermittent nature means there's probably a loose wire inside that is sometimes completing the circuit and sometimes not.

Another thing to check is the engine earth strap is tight. It may be enough for general running but causing problems with the charging circuit (as someone has mentioned before a loose earth on a battery has the same effect). Although seeing as you haven't said its hard to start and the engine seems to run fine it should be okay.

[Paul V]

Well it only goes with a jump start, the alternator came off my other car and was working fine on there. I'll have more fun over the weekend by the look of it.

Really annoying though as the Griff is off the road as well!

[jmorgan]

Is the 11 volts the battery? Or is that disconected. On our festa the battery is accross the alternator.

[Paul V]

its with the battery connected so the voltage would be coming from the battery not the alternator as its the same with the engine running or not!

[wedg1e]

The smaller wire is the sensing wire for the alternator. It detects the voltage at a point remote from the alternator to better allow it to judge the drain present and thus the amount of charge required: this is known as 'battery-sensing'. Older alternator designs sensed the voltage drop internally (known as 'machine-sensing') and were consequently less reliable.
You're obviously measuring the battery voltage at the larger terminals; the lack of anything on the smaller wire may be something as daft as a blown fuse or poorly-plugged connector - depends where they sense the voltage.
The alternator will be expecting to see something coming in to tell it what to do, in effect.

Ian

[Paul V]

I thought it was something like that, I have fitted another alternator plus clean up the plug connections etc. and that seems to have it charging, I’m now getting 13.9v at the alternator but only 13.2v at the battery so I’ll try cleaning the earths etc.