Alternator gauge

[mcgee500]

I got my 2020 Chevy Silverado April of 2020 with in a day or two I was back at the dealer asking why my alternator needle was on the negative side of the gauge. I was told that was normal. It didn't seem normal but OK I will live with it. Now February 2021 I got a update and the only thing I can find different is now the alternator needle is straight up or a little to the right ( more like where I thought it should be) but the dealer claims the update had nothing to do with it. Anyone else notice where your needle is now?????????????????

[Steve-2019]

What kind of "update" are you referring to?

[redwngr]

Alternator isn't controlled by an old school voltage regulator.

 

The ecm controls the alternator.

The output is based on a long list of things monitored by the ecm/bcm, so output variation is normal.

 

If the alternator isn't performing correctly -- computer is going provide a message.

 

 

 

Edited February 16, 2021 by redwngr

[redwngr]

Part of explanation, from upfitter documents:


Charging System Description and Operation

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.
The Charging System Description and Operation is
divided into 3 sections. The first section describes the
charging system components and their integration into
the electrical power management. The second section
describes charging system operation. The third section
describes the instrument panel cluster operation of the
charge indicator, driver information center messages,
and voltmeter operation.


Charging System Components

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 either the negative or positive
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.
Instrument Panel Cluster
The instrument panel cluster provides the customer
notification in case a concern with the charging system.
There are 2 means of notification, a charge indicator
and a driver information center message of SERVICE
BATTERY CHARGING SYSTEM if equipped.

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.

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.