Testing Altenator

Tesla · 16 Feb 2007 at 09:05

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?

paradigm · 16 Feb 2007 at 09:17

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.

Tesla · 16 Feb 2007 at 09:21

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?

BenST · 16 Feb 2007 at 09:33

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.