Testing Alternator

[Jim.ME]

No need to take it off and to AutoZone. Check the belt, check that the battery terminal of the alternator has battery voltage and then do the full field test. If the alternator charges the problem is likely the external regulator or wiring.

 

[old]

Your the one who is wrong which is normal for you. If you have a hard starting engine that wears the battery down so the alternator can/will put out 15 plus volts for a short time to get a fast charge on the battery

 

[MarkB_MI]

> Your [sic] the one who is wrong which is normal for you. If you have a hard starting engine that wears the battery down so the alternator can/will put out 15 plus volts for a short time to get a fast charge on the battery

That's not how voltage regulators work. A VR attempts to keep the output at a specific voltage, regardless of how much current it's providing. If the battery is exceptionally discharged, the voltage will actually be lower than nominal because the alternator isn't able to produce enough current to raise the battery voltage to nominal.

Most, if not all, voltage regulators have some sort of temperature compensation that raises the nominal voltage when it's cold and lowers it when the ambient temperature is hot. Which is why alternator voltage is always specified as a range.

 

[Geo-TH,In]

Would you believe my XT5 cadillac will charge at 15.5 volts when temps are close to zero?

 

[JMOR]

absolutely believe you

 

[MarkB_MI]

> Would you believe my XT5 cadillac will charge at 15.5 volts when temps are close to zero?

Newer GM vehicles constantly adjust the alternator voltage according to conditions in order to improve fuel economy and ensure the battery is properly charged. If you plug in a trailer, the voltage will bump up to ensure the trailer battery gets enough voltage. I suppose other manufactures do the same.

 

[Bhunt]

Yep I had one overchargering on a 1993 f350 I changed the regulator and the brushes. i spent about 30 dollars havent had an issue since. that was 4 years ago.