# Alternator voltage?



## chevrasaki (May 1, 2015)

Mine is the same way. I've only seen it drop to 12.6V when I bought a brand new battery and drove an 8 hour round trip. Only then did it drop briefly but it didn't stay there for long. From what I understand there are so many electronics that draw electricity, it will rarely stop charging/providing amps to the running electronics, mainly the daytime running lights.

I believe this behavior is normal.


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## Thms7722 (Nov 13, 2017)

I do have a question about testing the alternator if the voltage is normal to be as high as 15.1. I took my 2011 Chevy Cruze LT to auto zone and had the alternator tested and since the machine read 15.1 it’s saying the alternator is bad. How do you test the alternator for over charging?


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## ChevyGuy (Dec 13, 2014)

Thms7722 said:


> I do have a question about testing the alternator if the voltage is normal to be as high as 15.1. I took my 2011 Chevy Cruze LT to auto zone and had the alternator tested and since the machine read 15.1 it’s saying the alternator is bad. How do you test the alternator for over charging?


It can get that high. The Cruze also has a battery current sensor, so it's a little more sophisticated than your standard car charging system. The regulator is part of the BCM.


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## Thms7722 (Nov 13, 2017)

So is t say to say the old method of testing an alternator doesn’t work since the charging system actually does charge at 15.1volts?


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## jblackburn (Apr 14, 2012)

Thms7722 said:


> So is t say to say the old method of testing an alternator doesn’t work since the charging system actually does charge at 15.1volts?


I've seen it as high as 15.3 with a bad battery and in winter.


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## eddiefromcali (Aug 21, 2017)

Thms7722 said:


> So is t say to say the old method of testing an alternator doesn’t work since the charging system actually does charge at 15.1volts?


correct. The proper way would be to use a tech2 and send commands to the alt for various conditions, making sure it adjusts its output accordingly. If you disconnect the ground loop sensor, voltage should default to 13v or so...if it doesn't, the alt might be bad....that's the only DIY test w/o special tools that I know of. I've been dealing with this type of charging system in my truck since I got it 8yrs ago.


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## mikestony (Jan 17, 2013)

One of the things I monitor with the Torque App is battery voltage, and if the temperature drops below 45 degrees give or take, it goes up and stays pegged at about 15.1. And stays that way 45 minutes of highway driving to and from work.
Been doing that for the last 5 fall/winters. :whoknows:


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## eddiefromcali (Aug 21, 2017)

it does that to warm up the battery, totally normal


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## mikestony (Jan 17, 2013)

eddiefromcali said:


> it does that to warm up the battery, totally normal


Hmm, while I don't quite understand why it needs to do that, I'll take your word for it
And not to derail the OP's thread I have a simple (?) question then. Bear with me on this ....cold engine, 32 degrees out, start engine and alternator pegs out at 15 volts or so. Shut engine off. Replace battery with a warm (75 deg) battery. Start car again. Alternator should be more like 14.6 (or so) volts?


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## ChevyGuy (Dec 13, 2014)

mikestony said:


> Hmm, while I don't quite understand why it needs to do that, I'll take your word for it
> And not to derail the OP's thread I have a simple (?) question then. Bear with me on this ....cold engine, 32 degrees out, start engine and alternator pegs out at 15 volts or so. Shut engine off. Replace battery with a warm (75 deg) battery. Start car again. Alternator should be more like 14.6 (or so) volts?


No idea. The system can only guess the battery temperature based on other readings. So, that may not be a valid test. But it can sense the current going to the battery itself. My guess is that it raises the voltage as needed to get the charging current it wants. Traditional automotive systems were more of a constant-voltage design.


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## eddiefromcali (Aug 21, 2017)

mikestony said:


> Hmm, while I don't quite understand why it needs to do that, I'll take your word for it
> And not to derail the OP's thread I have a simple (?) question then. Bear with me on this ....cold engine, 32 degrees out, start engine and alternator pegs out at 15 volts or so. Shut engine off. Replace battery with a warm (75 deg) battery. Start car again. Alternator should be more like 14.6 (or so) volts?


in theory, yes....unless other conditions (Battery state of charge, accessories running, etc) are sensed that would also trigger a higher voltage output.


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## Cruzator (Dec 31, 2014)

This is for a diesel Cruze, but I would think that gas version would be similar.









*2014 Chevrolet Cruze 2.0L Eng Diesel*

*Charging System Operation*

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 turn ON signal circuit. The ECM monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 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:

Commanded Duty CycleGenerator Output Voltage10%11 V20%11.56 V30%12.12 V40%12.68 V50%13.25 V60%13.81 V70%14.37 V80%14.94 V90%15.5 V

The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.
*Battery Sulfation Mode*

The BCM will enter this mode when the interpreted generator output voltage is less than 13.2 V for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2-3 minutes. The BCM will then determine which mode to enter depending on voltage requirements.

*Charge Mode*

The BCM will enter Charge Mode when ever one of the following conditions are met.



The wipers are ON for more 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 V

When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9-15.5 V, depending on the battery state of charge and estimated battery temperature.

*Fuel Economy Mode*

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 state-of-charge 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 12.5-13.1 V. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.

*Headlamp Mode*

The BCM will enter Headlamp Mode when ever the headlamps are ON (high or low beams). Voltage will be regulated between 13.9-14.5 V.

*Start Up Mode*

When the engine is started the BCM sets a targeted generator output voltage of 14.5 V for 30 seconds.

*Voltage Reduction Mode*

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 V. The BCM will exit this mode once the criteria are met for Charge Mode.


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## Dolladog (Jun 25, 2014)

Badnewsracing.com has spark plug upgrades that's all bolt on top of the engine and come in all colors which gives major voltage upgrades to the car in case anyone was wondering.


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## eddiefromcali (Aug 21, 2017)

Dolladog said:


> Badnewsracing.com has spark plug upgrades that's all bolt on top of the engine and come in all colors which gives major voltage upgrades to the car in case anyone was wondering.


the LS7 ignition coil kit has nothing to do with alternator output


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## Spiike (4 mo ago)

This is interesting, makes a little bit of sense, but not a lot. using my car as a campervan sedan with a dual sense isolator solenoid on the house battery, it needs 13.3V to kick in, and kicks out at 12.8V so I have to remember to flip the lights on to charge the house batteries either while travelling or if i'm parked in the shade and the solar panel on the roof doesn't have sun. This is also strange behaviour from the smart alternator is when I have my 400W Car amp with a 80A fuse hits heavy bass with a 5 Farad Capacitor. Before the capacitor, the charging system would sense the voltage drop and always stick between 13.3-13.8V after long drives. Both having the extra 200 AH of battery being charged through a 4 gauge wire running both the car amp, i see 12.5-12.6V constantly! (with the 5 farad cap) even before the house batteries were installed. So i just need to remember to flip the lights on to put extra "juice" in the freezer batteries. Anyway to "trick" the system into charging at 12.8 instead of 12.4 ? i'll ask the dealership too when i'm there getting an oil change.

Steve



Cruzator said:


> This is for a diesel Cruze, but I would think that gas version would be similar.
> 
> 
> 
> ...


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