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DanDweller

What is Correct Alternator Voltage?

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Hi all, I just had an alternator shop look at my alternator because 1) I want to see if the transmission's hard shifting is related to a bad alternator, and 2) I am going to install a battery in the back of the van for vandwelling and one of the ways in which I will charge that battery is by a 20amp battery-to-battery charger made by Renogy, so I want to be sure my alternator is up to the task.

 

When we first started the engine, the alternator was putting out up to 14.8volts, but after a minute, it went down and stayed around 13.3-13.4.  When I kicked on the AC and brights, it dipped to 13.0 for a half-second and then went back to stay at 13.3-13.4.  The guys at the shop were not able to say whether the alternator is definitely faulty or perhaps is made to behave this way.  So I am putting the question on this forum before spending $235 to have them rebuild the alternator.  Thanks for any input.

 

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Sounds like it is operating normally.

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2 hours ago, kenryan said:

Sounds like it is operating normally.

Yeah, after posting this I also called a dealership and talked to a service tech who said it sounded normal.

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13.0v - 14.5v is the correct alternator voltage on a 12v system.

Edited by zalienz

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i expect around 14.2v but thats in europe if that makes any difference.

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Modern alternators may even go as low as 11V when needed and told by the ECU. You cannot measure it to diagnose. I went to an alternator shop when my battery went bad to ask them to measure it. They said it would be cheaper to buy a new battery to rule that out, they would need to remove the alternator from the car to diagnose it correctly.

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