Alternator, battery warning light

[darrenandsarah]

Now the problem is this, when I bought my Maestro DLX the battery light glowed very feintly and it was only really noticeable at night, using a multimeter it appears to be charging at about 13 volts when engine running and battery holds about 12.5 normally. But just lately the battery light glows alot more and when engine revs increase the light glows brighter not dimmer... would I be correct in thinking that this is a knackered diode and should I just drive it I have left the car for a week and still the battery has been charged.

Any thoughts?

[B18 GPC]

Or just check your earths ;) , Cleaning them up .. new earths if necessary

[Dean]

Is the belt the correct tension? Maybe worth changing it too.

[Steve H]

The charging voltage of only about 13V is a little suspicious. An alternator in good order should be able to maintain about 14 to 14.5V. Sounds like the charging current is weak for some reason.

Try putting a heavier load on (say headlamps and/or rear screen heater) and re-measuring the voltage. A weak charge would let the volts collapse back to 12V.

If it does this then (assuming the belt is tight enough to turn the alternator over) you've either got a duff alternator or the wiring loom is loose somewhere.

Could be diodes but it really sounds like the brushes are worn to the point where they are only just making contact. If this is the case, they can be replaced but an alternative is to get a secondhand alternator from a scrappy. And again, if it is brushes or diodes, it's only going to get worse..........:(

Steve H