Testing an alternator
Thread Starter
Burning Brakes
Joined: Sep 2004
Posts: 994
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Testing an alternator
I suspect the alternator on my '04 C5 is bad, so I removed it and am going to take it to autozone for them to test it tomorrow. But I was bored so I rigged up a way to hook the pulley to my electric drill and spun it up to around 1000 rpm with a multimeter hooked to the +12V terminal and ground (body of alternator). The meter showed no voltage.
My question is, does this prove it is bad? Or does it produce no voltage without some sort of control signal from the 4 post terminal on top?
My question is, does this prove it is bad? Or does it produce no voltage without some sort of control signal from the 4 post terminal on top?
Race Director
Joined: Sep 2002
Posts: 14,523
Likes: 24
From: Washington County, South UTAH
That is not a valid test. The alternator will not produce current, until the field is energized. The voltage regulator varies the amount of current into the field(stationary windings) to control the current output.
I have only tested alternators on the car, by buy passing the regulator and measuring output. There are other tests, shorted diode stc.
I have only tested alternators on the car, by buy passing the regulator and measuring output. There are other tests, shorted diode stc.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
alternator
put the alternator back on the car. plug it in
start the car and check volts at the battery lug.
if over 2.9V it's good if stays 11.0 to 11.5, go get another one
normal volts is 14.0 to 14.8
without jumpering the volt reg lug on the connector and placing a load on the other lug in the connector, it will not produce anything just spinning.
start the car and check volts at the battery lug.
if over 2.9V it's good if stays 11.0 to 11.5, go get another one
normal volts is 14.0 to 14.8
without jumpering the volt reg lug on the connector and placing a load on the other lug in the connector, it will not produce anything just spinning.
