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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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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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I ran a test on this for an extended time with an accurate meter directly on the battery terminals. The TC appears to be setup for Ford's "silver calcium" battery, used as standard equipment in Europe from Ford. It's a slightly different battery formula than is commonly used in US. It's supposed to last longer and resist sulfation, but requires a slightly higher system voltage. As a result, most Ford Europe vehicles are setup with 14.8V nominal alternator outputs, vs the more typical US domestic 14.4. 

 

As a matter of fact, I just removed the original battery and replaced it. The original battery had a black Motorcraft BXT-96R sticker on it, but there was clearly another sticker underneath, so I peeled it up and the actual original battery was a made in Germany Ford Silver Calcium T6 (DIN standard size T6). 

 

The slightly higher system voltage probably isn't a big deal, but you may not get as much life out of a standard lead-acid battery running in this electrical system. Wouldn't worry over it too much.  Not sure if Ford has taken this into account with their now specified replacement battery, a Motorcraft 40R.  It's not expensive, about the same as any other battery on the market. 

 

The 1.6L Ecoboost option has a battery charge regulator to reduce load on the engine. Mine is a 2.5L, and there's no additional regulator on the battery. The 1.6L will show different voltage on the battery than the alternator output. 

 

Edited by nuke

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