Testing Altenator

Soldato
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19 Jan 2003
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Bristol, UK
Testing Alternator

My friends battery keeps going flat, he replaced the battery but now that is flat to.

So either he has a short or a dodgy alternator. It's a '96 Fiesta (Mk3?, the boxy type) and has a 1.0l engine.

What is the correct procedure for testing how well the alty is functioning?
 
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Caporegime
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Leafy Cheshire
Get the car bump started, the voltage reading with the engine running should be a fair bit higher than 12v (probably 14-16v), then turn the engine off and take a reading (should be around 12-13v).

If the readings are the same, or very close, then it'd be a pretty certain bet that the altenator is shot.
 
Soldato
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paradigm said:
Get the car bump started, the voltage reading with the engine running should be a fair bit higher than 12v (probably 14-16v), then turn the engine off and take a reading (should be around 12-13v).

If the readings are the same, or very close, then it'd be a pretty certain bet that the altenator is shot.
Where should I measure it across? The battery terminals?
 
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Yes. Ideally to eliminate the possibility of loose or damaged wiring it would advisable to measure the voltage across the alternator ( +ve point to alternator body ) but I rarely have the need to do this.
 
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