Charging Systems in New cars. curious!

On New cars like a 08 vue, does the alternator stop charging while driving once the battery is fully charged to capacity? I've read that some systems do. For example, start up the car and the output is 14.5v to the battery. But once you drive it for several minutes, the regulator or ecm will tell the alternator to drop the voltage to 12.7. Is this true? I'm wondering because mines does exactly this. Matches to the tee. I recently changed my battery and or of curiosity I put a volt meter and watched the voltage as I drive. And that's the pattern I see.

I've not heard of a charging system that does that, and I'm not sure why they would design it that way. Generally a "smart charger" will start with a constant current mode, then switch to a constant voltage of something like 13.6 - 13.8 V and will maintain this voltage. Maintaining 12.7 V would not really make much sense as the current required by several systems would be higher to meet the power draw. The only logical reason I can come up with to do something like described would be to reduce the parasitic drag on the accessory belt, but then the designers could just as easily design the system to maintain 13.8V rather than 12.7. And that's basically what the system does today via the voltage regulator.

You have my curiosity piqued. Do you have a link to where you read about systems functioning as you describe?

-Rod

That's what I thought too. I only wished I saved the page. Ive been reading about of trying to figure out if my alternator is going bad. Came across where someone mentioned some charging systems do that. I found it odd myself. I'll see if I dig it out my history. But to give you my issue. I put a new battery since my battu was turning the engine slow this morning. Everything is squeaky clean. So I put a voltmeter to tthebattery. Start the car. 14.6v. 5 minutes later it slowly begins to drop to 13.6. Stays stay for another 5 minutes. Then it slowly drops to 12.7. Stays there forever. Only changes and goes back to 13.6 volts if I turn on lights or any other loads. If I leave it alone with nothing turned on, it drops back to 12.7. Only way I can get it to 14.5v is if I shut the engine off and turn it back on. Odd huh? But I came across a post from a guy who said some charging systems do that to maintain a long battery life. I was like, awesome! But I never heard of it before. I thought charging systems always charged at 14.5 on a good batt and alternator. Do I have a bad regulator? Or dead diode? Only hint I have of a bad regulator, I saw the voltage jump briefly to 14.9 for a full 2 seconds on one start up then drop to a steady 4.7. Im confused and hate to have a new battery get killed earlier due to a funny alternator. Ideas from you experts are appreciated. Also my lights don't flicker. Only flicker I had was my mileage lcd in the cluster assembly. That's gone now with the new battery. Lol. Im nuts.

I don't think charging to 12.7V would prolong the battery life, I'd be more inclined to say the continual transients on the battery every time the brake pedal is pressed, a turn signal is turned on, the blower fan kicks in, etc. would be far more damaging to the battery than a voltage of 13.8-14.4 that the battery is designed to handle, supported by a working alternator that is helping with the load.

What happens to the system voltage is you just increase the engine speed without turning on an accessory? Does the system voltage remain at 12.7V or does it increase? If it increases, I'd be inclined to say the alternator is not working properly, hence the low voltage at idle. Another thing to try would be to switch your meter to read ACV and see if you are getting more than say 0.2VAC at the battery. If so, the alternator would seem to be putting out more AC than the battery is able to filter off, pointing towards a failed diode or two.

You might need to find a factory service manual for your Vue to determine what your system voltage should be at warm idle with varying loads, then compare those numbers with your results.

If the manufacturers are starting to make charging systems the go in to standby mode as described in your first post, there will be a whole lot of misdiagnosed alternators by non-professionals (like me and the folks at the parts stores).

-Rod

I pulled up the service manual. It appears you read correctly. I've pasted in some interesting snippits from the manual.
------------------------------
Charging System Description and Operation
Electrical Power Management (EPM) Overview

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss1-1886438)The electrical power management (EPM) system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems with the battery and generator. This EPM system primarily utilizes existing on-board computer capability to maximize the effectiveness of the generator, to manage the load, improve battery state-of-charge and life, and minimize the system's impact on fuel economy. The EPM system performs 3 functions:
• It monitors the battery voltage and estimates the battery condition.
• It takes corrective actions by boosting idle speeds, and adjusting the regulated voltage.
• It performs diagnostics and driver notification.
The battery condition is estimated during ignition-off and during ignition-on. During ignition-off the state-of-charge (SOC) of the battery is determined by measuring the open-circuit voltage. The SOC is a function of the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open circuit voltage when the battery has been at rest for several hours.
The SOC can be used as a diagnostic tool to tell the customer or the dealer the condition of the battery. Throughout ignition-on, the algorithm continuously estimates SOC based on adjusted net amp hours, battery capacity, initial SOC, and temperature.
While running, the battery degree of discharge is primarily determined by a battery current sensor, which is integrated to obtain net amp hours.
In addition, the EPM function is designed to perform regulated voltage control (RVC) to improve battery SOC, battery life, and fuel economy. This is accomplished by using knowledge of the battery SOC and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.
The Charging System Description and Operation is divided into 3 sections. The first section describes the charging system components and their integration into the EPM. The second section describes charging system operation. The third section describes the instrument panel cluster (IPC) operation of the charge indicator, driver information center (DIC) messages, and voltmeter operation.
...
Generator

The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been converted into a direct current (DC) for use by the vehicles electrical system to maintain electrical loads and the battery charge. The voltage regulator integral to the generator controls the output of the generator. It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If the generator has field control circuit failure, the generator defaults to an output voltage of 13.8 volts.
...
Battery Current Sensor

The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes.
...
Charging System Operation

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss3-1886438)
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Battery Sulfation Mode
• Charge Mode
• Fuel Economy Mode
• Headlamp Mode
• Start Up Mode
• Voltage Reduction Mode
The engine control module (ECM) controls the generator through the generator field control circuit. It monitors the generator performance though the generator field duty cycle signal circuit. The ECM controls the generator through the generator field control circuit. The signal is a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The following table shows the commanded duty cycle and output voltage of the generator:
...
Charge Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss5-1886438)
The BCM will enter Charge Mode when ever one of the following conditions are met.
• The wipers are ON for than 3 seconds.
• GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
• The estimated battery temperature is less than 0°C (32°F).
• Battery State of Charge is less than 80 percent.
• Vehicle Speed is greater than 145 km/h (90 mph)
• Current Sensor Fault Exists
• System Voltage was determined to be below 12.56 Volts
When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9V and 15.5V, depending on the battery state of charge and estimated battery temperature.


Fuel Economy Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss6-1886438)The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amperes and greater than -8 amperes, and the battery SOC is greater than or equal to 80 percent. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5 and 13.1 volts. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.
Headlamp Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss7-1886438) The BCM will enter Headlamp Mode when ever the headlamps are ON (high or low beams). Voltage will be regulated between 13.9 and 14.5 volts.
Start Up Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss8-1886438)When the engine is started the BCM sets a targeted generator output voltage of 14.5 volts for 30 seconds.
Voltage Reduction Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss9-1886438)
The BCM will enter Voltage Reduction Mode when the calculated ambient air temperature is above 0°C (32°F). The calculated battery current is less than 1 ampere and greater than -7 amperes, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 12.9 volts. The BCM will exit this mode once the criteria are met for Charge Mode.

--------------------


Interesting info, thank you for bringing this function to my attention.


-Rod

I pulled up the service manual. It appears you read correctly. I've pasted in some interesting snippits from the manual.
------------------------------
Charging System Description and Operation
Electrical Power Management (EPM) Overview

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss1-1886438)The electrical power management (EPM) system is designed to monitor and control the charging system and send diagnostic messages to alert the driver of possible problems with the battery and generator. This EPM system primarily utilizes existing on-board computer capability to maximize the effectiveness of the generator, to manage the load, improve battery state-of-charge and life, and minimize the system's impact on fuel economy. The EPM system performs 3 functions:
• It monitors the battery voltage and estimates the battery condition.
• It takes corrective actions by boosting idle speeds, and adjusting the regulated voltage.
• It performs diagnostics and driver notification.
The battery condition is estimated during ignition-off and during ignition-on. During ignition-off the state-of-charge (SOC) of the battery is determined by measuring the open-circuit voltage. The SOC is a function of the acid concentration and the internal resistance of the battery, and is estimated by reading the battery open circuit voltage when the battery has been at rest for several hours.
The SOC can be used as a diagnostic tool to tell the customer or the dealer the condition of the battery. Throughout ignition-on, the algorithm continuously estimates SOC based on adjusted net amp hours, battery capacity, initial SOC, and temperature.
While running, the battery degree of discharge is primarily determined by a battery current sensor, which is integrated to obtain net amp hours.
In addition, the EPM function is designed to perform regulated voltage control (RVC) to improve battery SOC, battery life, and fuel economy. This is accomplished by using knowledge of the battery SOC and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.
The Charging System Description and Operation is divided into 3 sections. The first section describes the charging system components and their integration into the EPM. The second section describes charging system operation. The third section describes the instrument panel cluster (IPC) operation of the charge indicator, driver information center (DIC) messages, and voltmeter operation.
...
Generator

The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been converted into a direct current (DC) for use by the vehicles electrical system to maintain electrical loads and the battery charge. The voltage regulator integral to the generator controls the output of the generator. It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If the generator has field control circuit failure, the generator defaults to an output voltage of 13.8 volts.
...
Battery Current Sensor

The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes.
...
Charging System Operation

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss3-1886438)
The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:
• Battery Sulfation Mode
• Charge Mode
• Fuel Economy Mode
• Headlamp Mode
• Start Up Mode
• Voltage Reduction Mode
The engine control module (ECM) controls the generator through the generator field control circuit. It monitors the generator performance though the generator field duty cycle signal circuit. The ECM controls the generator through the generator field control circuit. The signal is a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The following table shows the commanded duty cycle and output voltage of the generator:
...
Charge Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss5-1886438)
The BCM will enter Charge Mode when ever one of the following conditions are met.
• The wipers are ON for than 3 seconds.
• GMLAN (Climate Control Voltage Boost Mode Request) is true, as sensed by the HVAC control head. High speed cooling fan, rear defogger and HVAC high speed blower operation can cause the BCM to enter the Charge Mode.
• The estimated battery temperature is less than 0°C (32°F).
• Battery State of Charge is less than 80 percent.
• Vehicle Speed is greater than 145 km/h (90 mph)
• Current Sensor Fault Exists
• System Voltage was determined to be below 12.56 Volts
When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9V and 15.5V, depending on the battery state of charge and estimated battery temperature.


Fuel Economy Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss6-1886438)The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 amperes and greater than -8 amperes, and the battery SOC is greater than or equal to 80 percent. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5 and 13.1 volts. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.
Headlamp Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss7-1886438) The BCM will enter Headlamp Mode when ever the headlamps are ON (high or low beams). Voltage will be regulated between 13.9 and 14.5 volts.
Start Up Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss8-1886438)When the engine is started the BCM sets a targeted generator output voltage of 14.5 volts for 30 seconds.
Voltage Reduction Mode

(http://sm.gpona.com:9001/si/showDoc.do?docSyskey=1886438&pubCellSyskey=37815&pubObjSyskey=1886438&from=sm&laborOpCode=&cellId=37815#ss9-1886438)
The BCM will enter Voltage Reduction Mode when the calculated ambient air temperature is above 0°C (32°F). The calculated battery current is less than 1 ampere and greater than -7 amperes, and the generator field duty cycle is less than 99 percent. Its targeted generator output voltage is 12.9 volts. The BCM will exit this mode once the criteria are met for Charge Mode.

--------------------


Interesting info, thank you for bringing this function to my attention.


-Rod

Excellent. That's what I'm seeing. I thought I did read right. Now, let me ask you this. Will jump starting a car at least 6 times in the past 1 yr 4 months and not trickle charge it cause the battery to die within a 2 year 2months usage? My battery was from walmart. Cheapest price I found 92 $. Yesterday I bought one from autozone that was 150 $. Different brand too. Ill post the brand soon. Some people claim walmart batts are compared to a 9 single double A battery in quality. Lol.

Shorod... Where did you get that from? Is it for 08 vue? I'm looking for aservice manual and I can't find 1.

Also, when it hits 12.7 steady, I do accelerate to all rpms and it does not change much. It will bounce to another fraction of a volts to maybe 12.8 Or 12.9v.If I do turn the lights on and turn the blower, it creeps up to 3.6 or 3.7v. Sound like it's functioning correctly I think. The battery has a cover with 2 large electrical lines feeding to the cover. I imagine that's the computer for the charging system that does that voltage control.

If you needed to jumpstart the car 6 times in the past year and a half, the jumpstarting is not going to be the reason the battery failed. Whatever's causing you to need to jumpstart the battery that often is the issue you need to resolve. Is it a bad battery, bad charging system, or something that's placing an excessive load on the battery?

I've not heard an abnormally large number of complaints regarding Wal-mart batteries. I've heard stories that there's only a couple of automotive battery manufacturers and all standard car batteries come from one of those manufacturers. If true, that doesn't necessarily mean that the quality won't be different for a battery made to Wal-mart's specifications versus an Autozone battery which might have slightly different specifications. I had poor luck with a few Duralast batteries so I've been going with Interstate batteries and have been quite satisfied. However, I've also heard of others having poor luck with Interstate. Everyone's likely to have a few defective items delivered to their store.

The information pasted above regarding how the charging system works is from the General Motors service manual for the 2008 Vue FWD (I suspect AWD would be the same). The manual I used is not a publicly available source, but if you are looking for a similar level of detail, your best bet might be to subscribe to Alldata.com. From my somewhat limited Alldata experience, the information they provide is from the factory service manuals. That's held true for several FoMoCo models, a Chevy, and a couple of Dodge minivans that I've subscribed to over the past several years.

-Rod

Thxs shorod. The jump starts I got was for user errors. Left the car on the ON position worth the lights on. And other times, door wasnt closed completely leaving the cabin light on. All the jumps were due t to those 2 factors. Besides the 6 jumps I got, I had 3 other times I drained the battery by sitting in the car waiting for a friend and again I left the the key on the ON position making the head lights not turn off. It's got day time running lights that are automatic. Those times I was lucky. I just turned off all accessories and waited 20 minutes. The battery was in good enough shape that it trickled charged itself. Enough to start the car on its on. But after 3 of those events, it didn't have enough performance to do it again. On the 4th dumb battery drain due to leaving the key on, I waited 30 minutes. It cracked bit no start. Waited 1 hour. Cranked and got really weak. That's when it would trickle charge no more and I had to get jump starts. That's why I think I killed the battery so soon. Now I'm very careful with my habits of leaving anything on when I wait for anyone and manually sit the auto day time running lights as soon as I turn the car off to wait for anyone or anything. The autozone guy charged the battery for about 45 minutes. Then did a load test. Came or as "defective battery, change battery". Aid it didn't want to hold a good charge no more. I told him is only 2 years old. But told him how many time I drained it by accident. Said chances are I wore it out. He said he can force charge it for another hour but it's better to replace it. I just replaced it. But that info you have me matches to the tee on how the voltage goes up and down. And also now all my windows go up and down fast. So I'm inclining to believe that the Walmart battery did get drained way to many times. I did check the acid before I went to replace it. It was full but there was some good acid corrosion on both terminals. But anyways, been keeping the Walmart battery was getting weaker, I figured when the system drops to economy charge, 12.7.... The battery did not like it at all. Want enough to hold juice due to the abuse I put it thru. Now as I type, everything is good. Windows move worth good speed. No flickering. And no weak engine turning at start up. Stats up really fat like a good healthy Bbattery should. And again the voltages match the description on your post very well. I did do a test this morning. Put the volt meter before starting it up with no head lights or accessories running. . Read 12.7v. Start the car. 14.5v. Let it idle. 4 minutes later, it slowly dropped to 13.6.v. 5 minutes later it slowly dropped to 12.7v. Stayed there for 10 minutes. I turned on the high beams, blower, defroster, stereo and wipers at full speed. Instantly the voltage stayed to climb to 13.7v. Took about 40 seconds to reach 13.7v. I let it idle for 3 minutes while watching the voltmeter. And it slowly climbed to 14.1. At that time I got tired of looking at the meter and just drove off. Sounds like it is working right according to the data sheet you posted. What's your opinion?

All this is new to me aswell. I thought all cars had a14.5 charge at all times. Im glad to find this out since I help others with car issues. I can imagine looking like adummy by recommending to change the alternator after seeing a low 12.7v charge at the post and not realizing it has this type of system!

Ok. Confirmed it with the stealer. Talked to a service adviser. He said on this car it will never be a constant 14.5 charge. It will range withing 9v to 16v. If they put it to a computer and it reads withing those ranges, it's a good healthy charging system. Thanks guys for your input.

Update: Battery was the issue. Car is driving like it should. Shorod, that EPM info helped tremendously! I would have called it B.S. if someone said that the charging system regulates the voltage all the way down to 12.7v while driving.

Here's another question. Looks like not too many non professionals are familiar with this charging system. Everyone I spoke to said to change the alternator Bavaria the voltage readings are very bad. But how would anyone be able to access the algorithm in the PCM or ECU to alter the charging stages? I'm sure a scan tool wouldn't be able to do it therfore is there any interfaces available for the general public 2 access the programming? Autozone carries that Scanner Guage2 tool that let's you clear codes and bonus of altering your idle rpm thru the ECU for fuel economy. . But doesn't touch anything else. I'm sure is recommended to keep the factory algorithm. But it would be nice to control the 14.7v stage. Just for the fact of being able to recharge a jumped battery longer.I believe that was most likely my case. A weak under charged battery for a lengthy period. Degrading the cells. Suggestions?

I also was ready to call BS on the article you read, but then remembered that I don't actually know everything. ;)

I doubt that even the Tech 2 device would allow the general public to alter the charging system parameters. I suspect that would require a dedicated firmware update, or possibly even reprogramming through JTAG or similar on the board itself of the charge controller. I really don't know.

-Rod

I also was ready to call BS on the article you read, but then remembered that I don't actually know everything. ;)

I doubt that even the Tech 2 device would allow the general public to alter the charging system parameters. I suspect that would require a dedicated firmware update, or possibly even reprogramming through JTAG or similar on the board itself of the charge controller. I really don't know.

-Rod

That's what I'm thinking aswell. It has to be a official dealer firmware update otherwise you will nullify the warranty. Thanks for the input.

Shorod, found this good article on these systems. Good info and I have a better understanding on how and why this implementation has been created. Makes complete sense, in theory it should make batteries last longer. In my case it was my own fault. It only lasted a little over a 2yr 1/4 span. I've read many times how people wonder why their batteries last only 2 years. Improper charging after jump starts. I recall on my battery, right before it almost didn't crank after shutting it down, a voltage of 10.9. And that's after reading 12.7v on a 15 minute trip. When the system was at a economy charge [12.7], it was just not enough for a tired abused battery. What's interesting, the ECU didn't bother sending a code to trigger the check engine light. Probable the programming parameters. But here's the link.

http://www.mpoweruk.com/bms.htm