Weird Charging Issue

[roaniecowpony]

Thats how mine was. But driving around for hours at 12.6v and only seeing 14.xV during deceleration has shown to result in the batteries bleeding down to about 65%.

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[THAW]

Another factor to consider is battery temperature.

During extensive observation of IBS live data (BCM) on my '23 2.0L, IBS Temperature appears overwhelmingly to be the primary determinant of running voltage. Roughly, I see low-to-mid 14 Volts at around 50° F (battery temp, not ambient), with approximately +/- 0.1 Volts for every 10° F difference. I wonder if longer/hotter drives can cause the battery to hit a temperature threshold that effectively shuts off continuous charging (at least for the some PCMs).

In this context, it's important to understand battery temperature is not easy to guess because it doesn't closely track ambient or even engine temperature; the battery heats and cools slowly, so lags by hours. Perhaps counterintuitively, the battery can be 30° F hotter at startup on a cold Winter evening if the vehicle sat with a warm engine after running for a short time earlier in the day than it is at startup on a hot Summer afternoon after sitting idle over a cool night. That is, it could start at 80° F on a 50° F evening, or at 50° F on an 80° F afternoon, and not budge much during typical commute time. For longer drives, how much and how fast the battery warms depends heavily on speed/airflow and ambient temperature; watching dash voltage may actually be the most reliable indicator of battery temperature, outside of JScan.

Interestingly, the 2.0L engine doesn't have an exhaust manifold on the battery side, and the highest IBS Temperature I've documented is 133° F, whereas Genesis Offroad has reported the BMS in a LiFePo4 shut down from hitting its 167° F threshold during a long journey in a 3.6L (and, as a result, now offers a heat shield for their metal battery tray).

 

[AmericanPatriot100]

There is a lot to read here. And I’m not an electronics guy by any means. I have a video of this happening to me last Friday. I mean it’s every day. But finally decided to record it. I’ll post it after I shorten it. When I was a tech I’d never seen battery voltage drop like this when everything is “working correctly”! Mine goes from 14.4v on deceleration down to 13.0v on acceleration. Which seems backwards in the scheme of things. I didn’t read everything posted in this thread because I’m not smart and lazy. What is the reasoning? Is the alternator bad or battery bad? My ESS is always off cause I press the button right after I start the jeep. So I don’t think that’s the issue. I know for a fact that I’ve forgotten to turn it off maybe a dozen times in 18k miles.

 

[Bob Burd]

It's perfectly normal with modern vehicles. When you decelerate, it increases the voltage which makes the alternator act as an engine brake. When you accelerate, it reduces the voltage so it does load the engine. This is essentially what a "smart" alternator is.

 

[THAW]

Mine goes from 14.4v on deceleration down to 13.0v on acceleration. Which seems backwards in the scheme of things. I didn’t read everything posted in this thread because I’m not smart and lazy. What is the reasoning? Is the alternator bad or battery bad?

If you have JScan, presumably you could monitor MODULES -> LIVE DATA -> Powertrain Control -> Target Charging Voltage (V) while driving to test whether the voltage fluctuation is controlled or a sign a sign of a performance issue.

 

[roaniecowpony]

There is a lot to read here. And I’m not an electronics guy by any means. I have a video of this happening to me last Friday. I mean it’s every day. But finally decided to record it. I’ll post it after I shorten it. When I was a tech I’d never seen battery voltage drop like this when everything is “working correctly”! Mine goes from 14.4v on deceleration down to 13.0v on acceleration. Which seems backwards in the scheme of things. I didn’t read everything posted in this thread because I’m not smart and lazy. What is the reasoning? Is the alternator bad or battery bad? My ESS is always off cause I press the button right after I start the jeep. So I don’t think that’s the issue. I know for a fact that I’ve forgotten to turn it off maybe a dozen times in 18k miles.

Keep in mind, it should not drop below 13.x volts into the 12.x volt area. If it does it isn't charging. Your battery should show 12.8 to 13.0 ish volts fully charged.

Disconnecting the ground terminal resets the IBS and it should charge at 14.x volts for a few start cycles. If it charges above 14.0v, it's likely nothing is wrong with th e alternator.

Your voltage regulator is in the PCM.

 

[WranglerMan]

Strange Electrical Issue.

BLUF. My Alternator isn’t charging my battery to 14V. I’m getting a constant 12.6V. But when I decelerate it jumps to 14V like normal. When I finally stop or accelerate, the voltage drops back to 12.6V.

2019 JL Rubicon. Running a dual battery system from Genesis Offroad. I recently changed out the batteries and they are brand new. Cold snap earlier this year zapped them. I bought the Jeep new and made a fair number of mods after the warranty ran out. Everything electrically has been fine, except for a short in USB and license plate light.

Everything was running well. Just completed a 12 hour long drive the day prior. Heading up a HWY to a trail, I hit a huge pothole I couldn’t avoid. The impact rattled our teeth. I didn’t notice anything immediately, but when I got to the trail, I noticed the alternator wasn’t putting out 14.1 – 14.2 volts like normal. I was getting a steady 12.5 to 12.7V. I put the battery on a charger when I got back from the trail and ensured I was topped off before making the 12hour drive home. After the trail it was at 75% but I did have to run my headlights because I returned after dark. After the 12-hr drive during the day, the battery was 82% charged.

On the way home I noticed something peculiar. I’m getting a consistent 12.6V at idle, at highway speed, higher RPMs while in park/neutral. But when I decelerate, either braking or coasting to a stop, the voltage jumps to 14.1, 14.2V like normal. As soon as I coast to, or brake to a stop the voltage drops back down to 12.6. If I need to accelerate after coasting to or braking to a stop, the voltage also drops. Why would momentum change how many volts I’m getting from the alternator.

I can only pass on my experience, I to run a Gen 2 Genesis system and my batteries are coming up on two years old in my 2018.

When I do charge them it’s not very often and before charging I always test with a decent battery tester and not rely solely on a voltmeter as a voltmeter only tells part of a batteries health.

After a good deep conditioning charge with one of several chargers I have my EVIC somtimes stays at 12.9 for days regardless of driving conditions and my tester always shows 100% SOC, CCA are above rated and SOH is above 80%

Others are correct the JL uses a smart alternator so it only puts outs what the batteries need, I would not solely rely on a voltmeter and get a battery tester to give you a better view of battery health.

 

[roaniecowpony]

I can only pass on my experience, I to run a Gen 2 Genesis system and my batteries are coming up on two years old in my 2018.

When I do charge them it’s not very often and before charging I always test with a decent battery tester and not rely solely on a voltmeter as a voltmeter only tells part of a batteries health.

After a good deep conditioning charge with one of several chargers I have my EVIC somtimes stays at 12.9 for days regardless of driving conditions and my tester always shows 100% SOC, CCA are above rated and SOH is above 80%

Others are correct the JL uses a smart alternator so it only puts outs what the batteries need, I would not solely rely on a voltmeter and get a battery tester to give you a better view of battery health.

What are you seeing on your dash voltmeter?

 

[Mguy]

Postings on this forum seem to show, apparently with all JL versions, that system voltage increases to battery charging range when the start battery is full and the engine RPMs are being reduced. The internet talk is that this is the "smart alternator" doing its thing for efficiency.

The talk is not consistent with what EEs know. A start battery at full charge can accept no more than a few tenths of an amp. An alternator outputting a few tenths of an amp, regardless of voltage, is not even consuming one horsepower. Regenerative power is only significant and useful when a vehicle battery much larger than a start 12V, like those found in EVs and hybrids, needs charging.

Perhaps someone will post some hard evidence that alternator equipped JLs use the charging system for regenerative power, however minuscule. Until then, my guess is that the observed full battery/voltage fluctuation is part of a JL diagnostic.

 

[WranglerMan]

What are you seeing on your dash voltmeter?

After a deep conditioning charge for 48 hrs my EVIC display on startup is normally 12.9-13.1 but most times it’s 12.9 and it will stay this way for several days then upon startup I’ll see 13.2-13-13.5 and then is slowly climbs back to 13.8-14.1 but drops pretty quickly on a decent highway drive.

i honestly don’t look at the EVIC voltage very often as I use a Motopower tester mostly to just monitor as it give me more info than a voltmeter

 

[roaniecowpony]

After a deep conditioning charge for 48 hrs my EVIC display on startup is normally 12.9-13.1 but most times it’s 12.9 and it will stay this way for several days then upon startup I’ll see 13.2-13-13.5 and then is slowly climbs back to 13.8-14.1 but drops pretty quickly on a decent highway drive.

i honestly don’t look at the EVIC voltage very often as I use a Motopower tester mostly to just monitor as it give me more info than a voltmeter

So when my voltage regulator was malfunctioning, it would eventually drain the battery down to 12.6v after 3-4 days. It would stay at that voltage. During highway cruise, my dash gauge would show around 12.6-12,8v. That's not enough voltage to fully charge the battery. It'll keep it around 60% charge. When I would disconnect the negative, it reset the IBS and I'd get 14.x volts for a day or so, then it would keep going lower with each successive start-drive cycle. That's how I determined the alternator was capable of making adequate charging voltage, but something was commanding it to low voltage. So, I changed the IBS and drove it a week. It did the same thing, and the battery eventually went to 60%. I had a spare PCM (original) and installed it. Problem solved. (the voltage regulator is in the PCM)

 

[Pape]

So when my voltage regulator was malfunctioning, it would eventually drain the battery down to 12.6v after 3-4 days. It would stay at that voltage. During highway cruise, my dash gauge would show around 12.6-12,8v. That's not enough voltage to fully charge the battery. It'll keep it around 60% charge. When I would disconnect the negative, it reset the IBS and I'd get 14.x volts for a day or so, then it would keep going lower with each successive start-drive cycle. That's how I determined the alternator was capable of making adequate charging voltage, but something was commanding it to low voltage. So, I changed the IBS and drove it a week. It did the same thing, and the battery eventually went to 60%. I had a spare PCM (original) and installed it. Problem solved. (the voltage regulator is in the PCM)

Can it be a loose pin at the connector of the PCM ?

 

[roaniecowpony]

Can it be a loose pin at the connector of the PCM ?

I would say No, based on the consistency of how it acted and how it immediately returned to a normal charging cycle after installing the old PCM. ...and has remained consistently normal charging.

 

[Pape]

I would say No, based on the consistency of how it acted and how it immediately returned to a normal charging cycle after installing the old PCM. ...and has remained consistently normal charging.

Ok, so you suspect a bad pcm or a issue with the tune ?

 

[roaniecowpony]

Ok, so you suspect a bad pcm or a issue with the tune ?

Bad voltage regulator circuit on the pcm is my suspicion.

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