Alternator Charging Voltage

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bennyb4928
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Joined: Fri May 13, 2022 9:05 pm

Alternator Charging Voltage

Post by bennyb4928 »

What is a normal charging voltage for these cars?

I was seeing volatges of 15v+ so I thought the internal voltage regulator on the alternator had gone bad.

I replaced the alternator with a new ACDelco alternator (92258220) and I am still seeing voltages of 15v+!

Is there another voltage regulator that I am missing? This car is new to me, but I haven't been able to find anything in the parts diagrams or when I poke around with my multi meter.

Any help would be greatly appreciated!
2013 9C1 Heron White - BTR LS3 Stage 2 Cam
JoeR
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Re: Alternator Charging Voltage

Post by JoeR »

The body module senses battery voltage and amperage and tells the PCM how to regulate the alternator. If you watch battery voltage while driving it may even drop to 12V or so. They generally want to keep the battery at 85% charge, and do whatever they need to do keep it there. 15V is pretty darn high though. I can't imagine why it would stay there on purpose for very long. They do have a de-sulfation mode, but it won't stay like that long term. Any chance you can get your hands on a scanner to see what the BCM sees for battery voltage? That'll help. Any chance your meter is reading incorrectly? I see that more and more lately.

Joe
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elc32955
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Re: Alternator Charging Voltage

Post by elc32955 »

Mine does the same thing, I've seen it has high as 15.4 volts and as low as 12.3 volts. Normal behavior for those regulators across multiple GM platforms. My 2008 GMC Sierra also did the exact same thing, I thought my alternator went south on me just before I was to enter the Ocala National Forest on a crossing on SR 40 from the center of Florida to the east coast. There's a TSB out on it somewhere talking about addressing the customer concern.

Unless you gave it to the shop for a core you have a good spare alternator on your hands. Shelve it or sell it :)

Thanks
Eric
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BluesBro
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Re: Alternator Charging Voltage

Post by BluesBro »

Yup, ran into this exact issue when I put the alpine amp in my car, amp was going into protect due to high voltage. My audio installer friend said it was just the normal way newer GM stuff is.
2014 Caprice PPV 6.0L - TSP Stage 1 Cam, Solo 3in Mach Cat Back, VCM OTR, Pedders Coilovers, HP Tuned
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Mooseman
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Re: Alternator Charging Voltage

Post by Mooseman »

You could put it in engineering mode by holding the select button and then turning the key to RUN and then START. You then see the voltage the PCM sees and the charge level. Mine hangs around 14V and has a 74% charge on the original 11 year old battery. And I also ripped out the second battery.
2011 Caprice PPV, former RCMP test vehicle, never put into service
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bstoner
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Re: Alternator Charging Voltage

Post by bstoner »

A little more info about the charging system:

Electrical Power Management Overview
The electrical power management 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 electrical power management 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 electrical power management 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 of the battery is determined by measuring the open-circuit voltage. The state-of-charge 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 state-of-charge 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 state-of-charge based on adjusted net amp hours, battery capacity, initial state-of-charge, 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 electrical power management function is designed to perform regulated voltage control to improve battery state-of-charge, battery life, and fuel economy. This is accomplished by using knowledge of the battery state-of-charge and temperature to set the charging voltage to an optimum battery voltage level for recharging without detriment to battery life.

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 V.

Body Control Module (BCM)
The body control module (BCM) is a GMLAN device. It communicates with the engine control module (ECM) and the instrument panel cluster for electrical power management (electrical power management) operation. The BCM determines the output of the generator and sends the information to the ECM for control of the generator turn on signal circuit. It monitors the generator field duty cycle signal circuit information sent from the ECM for control of the generator. It monitors a battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge. The BCM performs idle boost.

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.

Engine Control Module (ECM)
When the engine is running, the generator turn-on signal is sent to the generator from the ECM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator field duty terminal is connected internally to the voltage regulator and externally to the ECM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the ECM that a problem exists. The ECM monitors the generator field duty cycle signal circuit, and receives control decisions based on information from the BCM.

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 Cycle Generator Output Voltage
10% 11 V
20% 11.56 V
30% 12.12 V
40% 12.68 V
50% 13.25 V
60% 13.81 V
70% 14.37 V
80% 14.94 V
90% 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.

Auxiliary Battery Charging
The auxiliary battery is an option and can be used to supply electrical power to additional equipment that the customer may choose to add, without discharging the vehicle's primary battery. The auxiliary battery relay closes when the engine is running, in order to allow the generator to charge the auxiliary battery. The relay opens when the engine is off, so that the accessories are powered only by the auxiliary battery and will not discharge the vehicles primary battery, which is used for engine starting.

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 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.


Charge Indicator Operation
The instrument panel cluster illuminates the charge indicator and displays a warning message in the driver information center if equipped, when the one or more of the following occurs:
The engine control module (ECM) detects that the generator output is less than 11 V or greater than 16 V. The instrument panel cluster receives a GMLAN message from the ECM requesting illumination.
The instrument panel cluster determines that the system voltage is less than 11 V or greater than 16 V for more than 30 seconds. The instrument panel cluster receives a GMLAN message from the body control module (BCM) indicating there is a system voltage range concern.
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bennyb4928
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Re: Alternator Charging Voltage

Post by bennyb4928 »

JoeR wrote: Fri Jul 15, 2022 1:58 pm Any chance you can get your hands on a scanner to see what the BCM sees for battery voltage? That'll help. Any chance your meter is reading incorrectly? I see that more and more lately.

Joe
Unfortunately, I don't have access to a scanner. I have checked with two different meters and they both gave the same reading.
elc32955 wrote: Fri Jul 15, 2022 5:55 pm Unless you gave it to the shop for a core you have a good spare alternator on your hands. Shelve it or sell it
Already on the shelf and labeled!!
Mooseman wrote: Sat Jul 16, 2022 8:09 am You could put it in engineering mode by holding the select button and then turning the key to RUN and then START. You then see the voltage the PCM sees and the charge level. Mine hangs around 14V and has a 74% charge on the original 11 year old battery. And I also ripped out the second battery.
Good idea! I will give that a try. I did put two new batteries in the car about 3 months ago.
bstoner wrote: Mon Jul 18, 2022 9:02 am A little more info about the charging system:
Wow! That is some very valuable information. Thank you!!
2013 9C1 Heron White - BTR LS3 Stage 2 Cam
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