Normal Voltage Reading?

[AdmiralAckbar]

2003 2.4 auto, for the past week or so my TJ has been reading a little above 14v when running. This morning it was about half way between 14 and the next notch. It’s settled down a little bit at the time of taking the photo. Is this a normal read? Battery terminals are clean, battery and alternator are less than a year old.

The only other thing that’s also going on is that my radio will not turn on. It will sometime randomly turn on once it warms up, but on a start, no power.

 

[Jerry Bransford]

Normal. The voltage the alternator puts out while the engine is running varies on the battery's charge level. 14-something is typical while the engine is running. Without the engine running a fully charged 'wet' acid battery will measure 12.6 volts and a fully charged AGM battery will measure 12.8 volts.

 

[Rattler6]

13.7-14.7 volts when running is considered normal for most vehicles. A good rule of thumb for the TJ is that "normal" is when the guages stick straight up, give or take a little. Even your gas is normal in the pic

 

[LJDC]

Normal. The voltage the alternator puts out while the engine is running varies on the battery's charge level. 14-something is typical while the engine is running. Without the engine running a fully charged 'wet' acid battery will measure 12.6 volts and a fully charged AGM battery will measure 12.8 volts.

I found this thread in a search… I’m tracking down a small drain on the battery, but I think there is also another issue, maybe with the alternator.

With the (4.0) engine running at idle, and nothing extra plugged in, my alternator puts out about 13.3-13.4 volts. That seems low.

I first noticed after an all-day trail ride, when the battery was down to around 12 volts. I also had some other stuff charging during the day’s ride. I expected the alternator to be putting out 14 volts and above.

Is this a symptom of an alternator on the way out? I checked it at both the positive battery post and the post on the alternator.

If I’m going to replace it, is there a new part that will put out a little more, to support the other stuff I’m also charging while driving? I don’t mind upgrading the big electrical connections in the process, if necessary, to support it.

 

[Jerry Bransford]

I found this thread in a search… I’m tracking down a small drain on the battery, but I think there is also another issue, maybe with the alternator.

With the (4.0) engine running at idle, and nothing extra plugged in, my alternator puts out about 13.3-13.4 volts. That seems low.

I first noticed after an all-day trail ride, when the battery was down to around 12 volts. I also had some other stuff charging during the day’s ride. I expected the alternator to be putting out 14 volts and above.

Is this a symptom of an alternator on the way out? I checked it at both the positive battery post and the post on the alternator.

If I’m going to replace it, is there a new part that will put out a little more, to support the other stuff I’m also charging while driving? I don’t mind upgrading the big electrical connections in the process, if necessary, to support it.

The voltage output of the alternator varies with the state of the charge on the battery, your 13.3 to 13.4 is fine for a battery that is charged and doesn't need more charge. Over 14 is only going to be seen when the battery is low and needs charging. With the engine off a fully charged conventional battery measures 12.6 volts, a fully charged AGM battery measures 12.8 volts.

I'd charge the battery overnight (not just a couple hours) with a benchtop charger, not a trickle charger. Then take it to a battery retailer and ask them to do a "Load Test" on the battery which is the only way to know if the battery itself is good. They will place an amperage load that is 50% of its max rating for 15 seconds and measure its voltage at the end of 15 seconds. How much it dropped at the end of 15 seconds indicates if it is good or bad.

 

[LJDC]

Thank you. I don’t have a bench charger for a lead-acid battery, but I can get one. Would a trickle charger do over a longer time?

I just drove it for about 60 minutes—about 30 minutes twice (with a 2 hour break in between). At the end, the battery was at 12.6v, which is where it’s been for a while, even after long drives, and the alternator was putting out 13.4-13.5v.

To clarify the data from my previous post, when I checked the alternator the battery was at 11.6v and the alternator was still putting out 13.3-13.4v.

If the battery were bad, could it cause the alternator to feed that kind of voltage?

 

[macleanflood]

You don't get much voltage at idle. 12.8 ish. I usually slip a dime on the throttle cable on the throttle body to get the RPM up to 2k when winching. Then I'm around 14v.

Or at least that's what my alternator does...

-Mac

 

[C.J. Roberts]

During warmer weather, mine usually hits about 14.2 upon starting, then settles to 13.9. During colder weather, it has hit 15 briefly, but normally, again, upon starting, will easily crank mid14 for a good while, and eventually settle at about 14.1, maybe eventually getting down to 13.9.

 

[LJDC]

During warmer weather, mine usually hits about 14.2 upon starting, then settles to 13.9. During colder weather, it has hit 15 briefly, but normally, again, upon starting, will easily crank mid14 for a good while, and eventually settle at about 14.1, maybe eventually getting down to 13.9.

Is that at idle or revving the engine a bit?

 

[C.J. Roberts]

Is that at idle or revving the engine a bit?

It stays at 13.9 at idle, more while driving until it's warmed up. Once the battery recovers from starting, it settles an 13.9..

 

[LJDC]

I’m definitely not seeing that kind of voltage from the alternator…

 

[C.J. Roberts]

The voltage output of the alternator varies with the state of the charge on the battery, your 13.3 to 13.4 is fine for a battery that is charged and doesn't need more charge. Over 14 is only going to be seen when the battery is low and needs charging. With the engine off a fully charged conventional battery measures 12.6 volts, a fully charged AGM battery measures 12.8 volts.

I just drove it for about 60 minutes—about 30 minutes twice (with a 2 hour break in between). At the end, the battery was at 12.6v, which is where it’s been for a while, even after long drives, and the alternator was putting out 13.4-13.5v.

To clarify the data from my previous post, when I checked the alternator the battery was at 11.6v and the alternator was still putting out 13.3-13.4v.

I’m definitely not seeing that kind of voltage from the alternator…

Take another look at what Jerry Bransford said. 13.3 - 13.4 is fine.

 

[CharlesHS]

when I checked the alternator the battery was at 11.6v and the alternator was still putting out 13.3-13.4v.

IF the battery voltage measured 11.6V; there is a good chance that the battery is bad.
To be sure follow what Jerry posted above about charging the battery over night and have a local AP store load test the battery.
I would suggest you disconnect the negative battery terminal while charging the battery so there is no load on the battery over night.

 

[LJDC]

I’m not at all discounting what Jerry said. I just can't pull the battery and charge it yet, because I’m bogged down with work. I’ll try it this weekend. Meanwhile, I’ve had just enough time to check the battery when I’ve taken the Jeep out for one reason or another.

Take another look at what Jerry Bransford said. 13.3 - 13.4 is fine

 

[hear]

I usually slip a dime on the throttle cable on the throttle body to get the RPM up to 2k when winching.

You do what now?

 

[macleanflood]

So the throttle has a hard stop on the driver side. When you press the gas it pulls the cable passenger. You can move the throttle by hand... creating a gap between the stop...and shoving the right sized object in there gets you a higher idle.

My ten cents worth...

-Mac

 

[hear]

So the throttle has a hard stop on the driver side. When you press the gas it pulls the cable passenger. You can move the throttle by hand... creating a gap between the stop...and shoving the right sized object in there gets you a higher idle.

My ten cents worth...

-Mac

One of the 32RH diagnostic tests involves running the engine at a certain RPM, and I wondered how you did that. I guess the answer is to stack in the thin legos. A dime is about 18mm across, and a thin lego is 3.2mm, which means that each lego is worth about 178 RPM. r/Ididthemath

 

[LJDC]

.

 

[LJDC]

The voltage output of the alternator varies with the state of the charge on the battery, your 13.3 to 13.4 is fine for a battery that is charged and doesn't need more charge. Over 14 is only going to be seen when the battery is low and needs charging. With the engine off a fully charged conventional battery measures 12.6 volts, a fully charged AGM battery measures 12.8 volts.

I'd charge the battery overnight (not just a couple hours) with a benchtop charger, not a trickle charger. Then take it to a battery retailer and ask them to do a "Load Test" on the battery which is the only way to know if the battery itself is good. They will place an amperage load that is 50% of its max rating for 15 seconds and measure its voltage at the end of 15 seconds. How much it dropped at the end of 15 seconds indicates if it is good or bad.

I charged the battery. I haven’t taken it in to be tested yet. It appeared to reach 12.9v, but then it fell back down to 12.5v.

I’m going to let it sit in the Jeep to see if there’s something drawing it down. I’m wondering if there’s a current draw that’s causing the battery to discharge as it sits in the driveway.

Is there a nominal draw that’s common? I know certain things like the radio pull a small a mount of current to retain their settings (disconnect the battery and you lose your radio presets).

 

[Jerry Bransford]

Both the PCM and the radio have a 7/24 draw on the battery. Any aftermarket things like an aux amplifier that is staying on all the time? Even miswired relays for things like driving lights can cause a permanent draw when they're miswired to energize what they're connected to by being shut off and turned on to shut the device off.