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Checking Alternator

PhilW

PhilW

Nov 2, 2004
9,334
0
South Wales
Is it just a case of putting a multimeter on the main fuse in the engine bay, one of those metal ones and seeing if its showing any current?

I think my alternator is dead as the battery light is on and the engine dies after about 30 mins of driving which sees a fully charged battery drop to 6v then the engine cuts out.
 
To check current you need to put the multimeter in series, Phil.

So you need to take off the power cable to it and put one ond of the multimeter to the power cable and the other end to the terminal on the alternator.

Check that your multimeter can take the ampage first ;)
 
waste of time measuring the current anyway, as you'll only measure whats being drawn... which could be being drawn from the battery anyway.

Easiest check is measure the voltage at the battery, then get someone to rev the engine up to 2500-3000rpm while you measure again, the voltage should be around 12.6v at idle, and 14.4v at 2500-3000rpm, as the alternator voltage has to overcome the battery voltage to allow the battery to charge.

If your not getting this, then you need to start testing the individual components on the alternator such as the rectifier diodes, and checking the windings arn't shorted to ground, or it could be the voltage regulator.
 
I have a Scangauge thats plugged into the ODB port and that shows a full charged batter at about 13v then its just continually drops til all things stop working on the engine just shuts down.
 
it's shagged then mate.. if your confident with electronics you could check out the rectifier and regulator (altho i'm not entirely sure it's easily replacable on these)

but for ease and peace of mind, i'd replace the whole unit.
 
Last edited:
Bringing this back from the dead, got another alternator/charging.battery problem.

My battery basically doesnt hold charge and my Scangauge is reporting 12.5-12.8v whilst running and not really dropping or increasing.

Any ideas?

Do alternators fail slowly?
 
Phil, to test this you could start the car, and then disconect the battery, and see if the car then runs from the alternator. If it does that the alternators ok, if it cuts out, that it would seem that the battery is powering the car.

I think Ibiza Alex was selling an alternator, i think it was painted black.
 
Surely at a lower voltage tho tom it would still run, but wouldnt be enough to charge the battery?

Im gonna get my spare one fixed and use that.
 
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