not sure if my answer is correct, but our alternators may be designed to charge only when nec. If the battery is fully charged its gonna back off and your seeing battery voltage instead of alternator voltage.
---------- Post added at 09:35 PM ---------- Previous post was at 09:34 PM ----------
This may offer some inight, f150 charging system theory of operation
System - 3.5L Duratec (209kW/284PS)/3.5L EcoBoost (272kW/370PS)/5.0L 32V Ti-VCT - System Operation and Component Description
System Operation
System Diagram
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Network Message Chart
Module Network Input Messages - Body Control Module (BCM)
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Module Network Input Messages - Instrument Panel Cluster (IPC)
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Module Network Input Messages - Powertrain Control Module (PCM)
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Charging System
The PCM (powertrain control module) controlled Smart Charge charging system determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator. The Smart Charge charging system sets Diagnostic Trouble Codes (DTCs) when a charging system fault is present. All of the Diagnostic Trouble Codes (DTCs) can set continuous faults, but not all Diagnostic Trouble Codes (DTCs) set as on-demand faults.
This system uses 2 communication lines between the PCM (powertrain control module) and the generator/voltage regulator: A generator communication (GENCMD) line communicates the desired setpoint from the PCM (powertrain control module) to the voltage regulator, and a generator monitor (GENMON) line communicates the generator load and error conditions to the PCM (powertrain control module). Both of these use PWM (pulse width modulation). The PCM (powertrain control module) sends the GENCMD command only when it is necessary to adjust the voltage setpoint. If the setpoint does not need to be changed, several seconds may elapse between PCM (powertrain control module) GENCMD commands. This normal operation appears in the PID (parameter identification) as occasional bursts of pulse-width commands. In addition to these two circuits, a third pin on the voltage regulator, the "A" circuit pin, is dedicated to monitor, or sense, the battery voltage.
The PCM (powertrain control module) simultaneously controls and monitors the generator output. When the current consumption is high or the battery is discharged, the PCM (powertrain control module) raises engine speed as needed to increase generator output. The generator charges the battery and at the same time supplies power for all of the electrical loads. The battery is more effectively charged with a higher voltage when the battery is cold and a lower voltage when the battery is warm.
The PCM (powertrain control module) turns off the generator during cranking to reduce the generator load and improve cranking speed. Once the engine starts, the PCM (powertrain control module) slowly increases generator output to the desired voltage.
The PCM (powertrain control module) reports any charging system faults and sends a message through the HS-CAN1 (high speed-controller area network 1) to the BCM (body control module). The BCM (body control module) controls the charging system warning indicator by sending a message through the GWM (gateway module A) to the IPC (instrument panel cluster). The status of the PCM (powertrain control module) charging system warning indicator and/or message is confirmed by viewing PCM (powertrain control module) PID (parameter identification) generator fault indicator lamp (GENFIL). Any charging system fault detected by the PCM (powertrain control module) results in 1 or more Diagnostic Trouble Codes (DTCs) being set and the PID (parameter identification) GENFIL having a status of On. If equipped with a charging system warning indicator, the IPC (instrument panel cluster) turns the indicator on or off. If equipped with a message center, the IPC (instrument panel cluster) displays a CHECK CHARGING SYSTEM message. In some instances, the CHECK CHARGING SYSTEM message may not display if the ignition is on and the engine is off.
Under certain circumstances, the charging system may have a concern but still keeps the battery charged and the vehicle running. GENCMD normally initiates charging but with a fault in this circuit, the generator can self-excite and start charging on its own. The charging system warning indicator is illuminated and/or the CHECK CHARGING SYSTEM message is displayed, and the generator operates in a default mode (approximately 13.5-volts).
Electrical Energy Management
NOTICE: When any vehicle module is being programmed, connect an external battery charger to make sure the module programming is completed without interuption due to the load shedding feature becoming active. The external battery charger must maintain a system voltage above 13 volts. This may require a charger setting higher than the lowest charge setting. The external battery charger negative connection must be made to an engine or vehicle chassis ground and not the negative battery terminal. If the connection is to the negative battery terminal, load shedding may begin and module programming may be corrupted. After charging has begun, start the engine to clear any load shed states and then turn the engine off and proceed with programming.
This vehicle is equipped with an Electrical Energy Management system which manages battery charging and monitors the battery state of charge. The Electrical Energy Management system software is housed in the BCM (body control module). It has the algorithms and control structure for the Smart Regenerative Charging, and Load Shed Control Strategy. The Electrical Energy Management system is equipped with a battery monitoring sensor and generator current sensor to monitor the battery. These sensors serve as input to the Electrical Energy Management system software. If the sensors malfunction due to wiring issues or failure, a DTC (diagnostic trouble code) will be set. In most cases the Electrical Energy Management system functions will be turned off until the sensor operation is restored.
Battery State of Charge
The BCM (body control module) uses the battery current sensor to keep track of the battery state of charge. During a drive cycle the Electrical Energy Management software adjusts the battery state of charge up during charging, and down during discharge.
During rest periods with the key off, and the vehicle enters sleep mode, the BCM (body control module) automatically recalibrates the Battery State of Charge. It takes 8 hours in sleep mode, with the vehicle undisturbed, no doors opened or keyless entry buttons pressed, and the total vehicle current draw less than 300mA, to calibrate the battery state of charge to a high accuracy. If the system draw has not allowed the battery state of charge to calibrate over the previous 7 days, the state of charge quality factor changes to identify this and some Electrical Energy Management system functions may be temporarily turned off until a calibration takes place.
Engine Off Load Shed
When the engine is off, and the BCM (body control module) determines the battery state of charge is below 40% or 10% of the charge has been drained or 45 minutes have elapsed, a load shed message is sent over the CAN. This message turns off the audio/navigation system to save the remaining battery charge. Under this condition, the FDIM (front display interface module) displays SYS OFF TO SAVE BATT (without navigation) or BATTERY SAVER - SYSTEM OFF PLEASE START THE ENGINE (with navigation) to notify the driver that battery protection actions are active.
Engine off load shed occurs when the engine is not running, and the ignition is in the ACC or RUN position. To clear the load shed state, restart the engine.
NOTE: To maintain correct operation of the load shed system, any electrical devices or equipment must be grounded to the engine or chassis ground and not the negative battery terminal. A connection to the negative battery terminal may cause an inaccurate measurement of the battery state of charge and may cause incorrect load shed system operation.
When the ignition is in the RUN position and load shed occurs, the IPC (instrument panel cluster) message center displays either TURN POWER OFF TO SAVE BATT (base message center) or TURN POWER OFF TO SAVE BATTERY (optional message center). The audio/navigation system will shut down after the message center displays it's warning.
If a fault occurs with the battery current sensor or circuit(s), the only engine off load shed strategy is a 45 minute timer. After 45 minutes have elapsed, the audio/navigation system turns off. To clear the load shed state, restart the engine.
Engine Running Load Shed
When the BCM (body control module) and/or PSCM (power steering control module) voltage is low, with the engine running, a message is sent by the BCM (body control module) to either minimize or shut down the climate controlled seats, rear defrost, heated mirrors and DATC (dual automatic temperature control) blower motor to improve system voltage. Under this condition, the IPC (instrument panel cluster) message center displays either LOW BATTERY LESS FEATURES (base message center) or LOW BATTERY FEATURES TEMPORARILY TURNED OFF (optional message center) to notify the driver that battery protection actions are active.
For more information on message center messages, Refer to the Owner's Literature or
Refer to: See: Instrument Panel, Gauges and Warning Indicators > Components > System Operation and Component Description Message Center - System Operation and Component Description (413-01 Instrumentation, Message Center and Warning Chimes, Description and Operation).
There are 3 states of engine running load shed:
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Battery Charging or Jump Starting
To charge or jump start the vehicle, connect the positive cable to the battery positive post. It is preferred to connect the negative cable to a vehicle ground and not the battery negative terminal. Connecting directly to the negative battery post can have an adverse effect on the Electrical Energy Management system. For a good connection point, follow the cable from the battery negative post to the vehicle body connection (typically on the shock tower sheet metal) and connect there.
If the battery is jump started or charged, the BCM (body control module) must recalibrate the battery state of charge. Engine off load shedding may occur if the vehicle is operated before the BCM (body control module) calibrates the new battery state of charge.
NOTICE: DO NOT reset the battery monitoring system using the diagnostic scan tool. This reset is reserved for new battery installation. Resetting the battery monitoring system will clear the learned battery data, the battery time in service, and will affect the aging algorithm parameters, which have been learned since the installation of the battery.
Battery Replacement
If the vehicle battery is replaced, it is very important to perform the BMS Reset using a diagnostic scan tool. If the battery monitoring system reset is not carried out, it holds the old battery parameters and time in service counter in memory. Additionally it tells the system the battery is in an aged state and may limit the Electrical Energy Management system functions. For more information,
Refer to: See: Battery > Components > System Operation and Component Description Battery and Cables - System Operation and Component Description (414-01 Battery, Mounting and Cables, Description and Operation).
Component Description
Generator
The generator is equipped with an electronic internal voltage regulator.
Generator Current Sensor
The generator current sensor is attached to the generator B+ cable. It is supplied a 5-volt reference voltage and a ground from the PCM (powertrain control module). The generator current sensor is a Hall-effect sensor that supplies an analog feedback signal to the PCM (powertrain control module). The PCM (powertrain control module) uses this information for battery charging strategy and idle stability and torque control.
Battery Current Sensor
The battery current sensor is attached to the battery negative cable. It is supplied a 5-volt reference voltage and a ground from the BCM (body control module). The battery current sensor is a Hall-effect sensor that supplies an analog feedback signal to the BCM (body control module). The BCM (body control module) reads the battery current sensor feedback voltage to determine how much current is flowing through the battery ground cable. The BCM (body control module) uses this information for battery state of charge.
Powertrain Control Module (PCM)
The PCM (powertrain control module) monitors and controls the charging system.
