Alternator woe's

[Matt Mason]

My chaging light stays on!
Having checked the battery voltage it shows its not charging when running. The voltage stays the same when the engine speed is increased and go's down if the lights are put on.
ALSO if you remove the earth lead it stops the engine dead , this should not happen!
Is there a way to test the alternator other than putting lights on and hearing a rev drop??

Whats the best way???

Thanks Matt

Matt

[Richard B]

I think you've just about proved it.

But..........

Is the main cable to the battery in a good condition? If this cable  has a dodgy connection then that can cause the alternator to fail.

[Matt Mason]

All sorted ...bulb/holder some how was not supplying voltage to the ind conection on the alternator....just changed the bulb and low and behold all worked again!!!
The glass of the bulb had become unatached from its screwfitting yet it still just lit up ..but why it didnt pass on the voltage down to the alternator iam stumped.

Watch out for this annoying fault....it drove me mad. >:(


Matt

[Pete Lewis]

worth a note the warning light wattage controls the cut in voltage,, bigger bulb =quicker cut in
usefull if playing around and cant get the right pulley size/revs at idle  peter

[mark spit]

Re alternator checking,
Use a multimeter, I recently put a brand new one on my Astra and had no charge at battery when running.

Stuck until I checked between the alternator output post and the alternator body, 15V. but between the post and anywhere else I could only get 12 V which made it look like it wasn't charging.
There was a 3V drop across the bolt connections which earth the alternator body to the car itself. Any other bad earth connection between the alternator and the -ve battery terminal will do similar.
Yours
mark