Alternator charging question

[Frostbit]

I noticed the dash voltmeter on my wife's 3.0 diesel with ESS (we disable it every start) acts differently than any other vehicle I've owned. It shows a charge into the mid 14's if coasting or braking but down into the 12's when driving under power. Is this how the Pentastar and 2.0 charge as well??????????

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[Goosed]

3.6 pent here and I get the same sometimes.

 

[Bob Burd]

Yes. It's a smart alternator that will hold off charging when the engine is working hard, and when the engine load is light it ramps up charging.

 

[SilentSkut]

Yes. It's a smart alternator that will hold off charging when the engine is working hard, and when the engine load is light it ramps up charging.

I believe this is correct and has to do with gas mileage efficiency. FWIW, I rebuild alternators for a living.

 

[Maverick909]

yup my 3.6 is the same. nothing to worry about!

 

[Frostbit]

Thank you everyone. Love this forum!! The reason I asked is a got a "big brother" alert via email from Jeep that there was an issue with my charging system even though there was no alert in the vehicle. I had not paid any attention to the voltmeter before the alert but then noticed what I thought was the odd charging pattern I mentioned.

My other vehicles are old school Cummins Rams and they charge rather linearly with an increase with RPM's.

I took the 3.0 Wrangler to the dealer under warranty as the email strongly suggested. I explained everything I've mentioned about the observed charging pattern. The dealership up here in Alaska had never seen a 3.0 Wrangler before.

The tech felt it was not charging at a high enough rate at idle and the Alternator was faulty. There is no replacement alternator available for months as the 3.0 uses a different one.

I took my rig back from the dealership and it continues to run fine and the charging pattern remains as I outlined above.

I suspect the dealership and tech have no clue how these alternators work as far as charging cycle and presumed there was a problem having no experience with the 3.0.

On the 3.0 forum two others have also gotten the same "big Brother" message and ended up with their dealerships saying there was no problem.

I'm going to link this thread onto the 3.0 forum so the others there can read it.

Thanks again!!

 

[D90John]

Thank you everyone. Love this forum!! The reason I asked is a got a "big brother" alert via email from Jeep that there was an issue with my charging system even though there was no alert in the vehicle. I had not paid any attention to the voltmeter before the alert but then noticed what I thought was the odd charging pattern I mentioned.

My other vehicles are old school Cummins Rams and they charge rather linearly with an increase with RPM's.

I took the 3.0 Wrangler to the dealer under warranty as the email strongly suggested. I explained everything I've mentioned about the observed charging pattern. The dealership up here in Alaska had never seen a 3.0 Wrangler before.

The tech felt it was not charging at a high enough rate at idle and the Alternator was faulty. There is no replacement alternator available for months as the 3.0 uses a different one.

I took my rig back from the dealership and it continues to run fine and the charging pattern remains as I outlined above.

I suspect the dealership and tech have no clue how these alternators work as far as charging cycle and presumed there was a problem having no experience with the 3.0.

On the 3.0 forum two others have also gotten the same "big Brother" message and ended up with their dealerships saying there was no problem.

I'm going to link this thread onto the 3.0 forum so the others there can read it.

Thanks again!!

 

[D90John]

I had the same problem with my new JLUR diesel. Same emails from big brother. Same issue with the dealer in Eureka, CA who had never seen a diesel wrangler. After 4 hours in the Covid-19 waiting room the tech found an info sheet that stated a similar problem has occurred to many new diesel owners and that the alternator is working as it should. Thanks for posting that write up!

 

[Frostbit]

I had the same problem with my new JLUR diesel. Same emails from big brother. Same issue with the dealer in Eureka, CA who had never seen a diesel wrangler. After 4 hours in the Covid-19 waiting room the tech found an info sheet that stated a similar problem has occurred to many new diesel owners and that the alternator is working as it should. Thanks for posting that write up!

Thank you. I'll give my dealer a curtesy call tomorrow. They said at the time they had mine that there were no service bulletins on the problem.

 

[word302]

Yes. It's a smart alternator that will hold off charging when the engine is working hard, and when the engine load is light it ramps up charging.

Well sort of. It charges when the battery needs it, not based on load.

 

[Bob Burd]

Well sort of. It charges when the battery needs it, not based on load.

If you step on the gas you'll see the alternator voltage drop, reducing its load on the engine. Conversely, if you start coasting downhill, you'll see the voltage go up - the alternator is loading the engine as a braking mechanism (however modest). The "smart" part of the alternator is how it adjusts to the engine's work load, not the needs of the battery. If your battery is low enough, it will overwrite the above adjustments and peg the alternator voltage to 14.x volts - this is typical if you make short drives. If you drive longer or use a battery tender, the alternator behaves as described above.

 

[word302]

If you step on the gas you'll see the alternator voltage drop, reducing its load on the engine. Conversely, if you start coasting downhill, you'll see the voltage go up - the alternator is loading the engine as a braking mechanism (however modest). The "smart" part of the alternator is how it adjusts to the engine's work load, not the needs of the battery. If your battery is low enough, it will overwrite the above adjustments and peg the alternator voltage to 14.x volts - this is typical if you make short drives. If you drive longer or use a battery tender, the alternator behaves as described above.

Like I said, not exactly. For the first couple days after reconditioning my batteries with the Odyssey 20 amp charger I don't see 14 volts on the voltmeter, even at idle. That leads me to believe that battery needs do infact impact the alternator output.

 

[Bob Burd]

I'd be curious to see what you see when decelerating. It *should* jump up to 14.x, but perhaps the Odyssey charger brings it to a higher resting voltage than my charger does, and as you say, it sees no need to charge the battery under any condition.

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