Failing Alternator

[ImAJeepskate]

Was almost done with a 300 mi road trip and noticed that my voltage was only around 12.8v while doing 67 mph in 5th gear. It would never go over 13v unless I was off the throttle engine breaking (manual transmission). I assume this is because of less draw from the ignition. But shouldn't the alternator be at 14v or at least above 13v? Also I have the standard (non-high output) alternator.

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[rustyshakelford]

I agree with what’s been said. Completely normal

Brett

 

[LincolnSixAlpha]

I agree with the other two comments. Also worth noting that if your alternator was failing, your vehicle would soon stop running as the batteries, on their own, do not have enough juice to fire the fuel injectors, among all the other electrical needs of the vehicle.

Also, I own/drive BMW motorcycles, and have so for years. They integrate well with Garmin rebranded BMW Navigator GPS units. There's an information page that gives you particular stats such as current fuel consumption, range to empty, as well as a voltmeter. Like the Jeep, the alternator output is a little higher on startup, until the battery is topped off, then drops to low-mid 12's. I had a battery at one point with a bad cell, the voltage output was always in the 14's, which clued me into the issue.

 

[ImAJeepskate]

I agree with the other two comments. Also worth noting that if your alternator was failing, your vehicle would soon stop running as the batteries, on their own, do not have enough juice to fire the fuel injectors, among all the other electrical needs of the vehicle.

Also, I own/drive BMW motorcycles, and have so for years. They integrate well with Garmin rebranded BMW Navigator GPS units. There's an information page that gives you particular stats such as current fuel consumption, range to empty, as well as a voltmeter. Like the Jeep, the alternator output is a little higher on startup, until the battery is topped off, then drops to low-mid 12's. I had a battery at one point with a bad cell, the voltage output was always in the 14's, which clued me into the issue.

Appreciate the explanation!

 

[smokinjeep]

I dont know a thing about alternators, volts, amps etc but agree with the other three because i want to sound like I know something.

 

[LincolnSixAlpha]

I dont know a thing about alternators, volts, amps etc but agree with the other three because i want to sound like I know something.

Well, to be honest, I'm no electrician either, I just found out the hard way with a few of my daughter's vehicles in which suffered battery, AND alternator problems. Anyhow, cars today are so, so much more complicated than they were many years ago. I remember driving home in my 74 Subaru in the mid 80's on just the alternator. The battery had died. Lights would go dim when I came to stop signs, then bright again as the engine speed increased.

 

[melendez69]

My JL always cranks up at 14.2v, & I've taken her on a few 200+ mile trips this year. By the time I got home each time, it would drop down to about 13v. I used to have voltage anxiety, but I've learned what the gents here are saying. Perfectly normal.

But I still keep a trickle charger.

 

[Shenanigans]

Mine consistently runs at 14.2 to 14.3 volts.

 

[Moto_21]

Mine consistently runs at 14.2 to 14.3 volts.

So does mine or higher. Makes me think one of the batteries is on the way out. When i first got the jeep it would fluctuate as its supposed to. Now its a constant 14.2-14.7

 

[Shenanigans]

Charging systems are designed to be around 14 volts while the motor is running. A healthy battery that isn’t being charged by an alternator should be around 12.6 volts. I’ve had all sorts of charging systems as I was a huge stereo guy. Dual alternators, isolated 12 volt systems with six 6 volt batteries, multiple 12 volt batteries, etc.... I was a 12 volt freak for a very long time.

 

[Moto_21]

Charging systems are designed to be around 14 volts while the motor is running. A healthy battery that isn’t being charged by an alternator should be around 12.6 volts. I’ve had all sorts of charging systems as I was a huge stereo guy. Dual alternators, isolated 12 volt systems with six 6 volt batteries, multiple 12 volt batteries, etc.... I was a 12 volt freak for a very long time.

Yeah when i check resting voltage on my display before i start it up in the morning its at 12.3-12.4 volts

 

[Markham]

I have an auto, but when I’m on the throttle the voltage drops, when I coast it goes back up.

 

[Token]

I have an auto, but when I’m on the throttle the voltage drops, when I coast it goes back up.

Go WOT.

You’ll see it go up again as your A/C clutch disengages.

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