Alternator - smart charge (Ford)

The purpose of this test is to check the command, feedback, and output voltage signals from a Ford-type smart charging alternator.

How to perform the test

View connection guidance notes.

1. Use manufacturer’s data to identify the alternator command, feedback, and output circuits.
2. Connect the high amp clamp into PicoScope Channel A, select the 200 A range and zero the clamp.
3. Connect the high amp clamp around the alternator B+ cable.
4. Connect PicoScope Channel B to the alternator feedback circuit.
5. Connect PicoScope Channel C to the alternator command circuit.
6. Start the engine and allow it to idle.
7. Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
8. Start the scope to see live data.
9. Switch on electrical consumers and vary engine RPM whilst observing your waveforms.
10. With your waveforms on screen stop the scope.
11. Stop the engine.
12. Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.

Example waveform

Engine idle, alternator under light load.

Engine at idle, alternator under moderate load.

Waveform notes

These known good waveforms have the following characteristics:

• At low loads the alternator output current (Channel A) is approximately 14 A. With additional electrical loads, such as those from the heated screen, main beam headlights, and heater blower, the output current increases to 70 A.
• The alternator feedback signal (Channel B) is a pulse-width-modulated voltage waveform dependent on the alternator current output: with a low load, the waveform is around 0 V for approximately 60% of its cycle duration; at high loads it is around 12 V for approximately 100% of its cycle duration.
• The alternator command signal from the ECM (Channel C) is a positive-switched pulse-width-modulated voltage waveform. With no load, it remains off, at 0 V. With moderate electrical loads, it is around 13 V for approximately 63% of its cycle duration.

Waveform Library

Go to the drop-down menu bar at the lower left corner of the Waveform Library window and select, Alternator command signal.

Further guidance

When the engine is running, an alternator generates electrical energy to supply the vehicle’s onboard electrical systems and replace the battery charge consumed during cranking.

Smart charge systems are able to balance these requirements against the needs of the driver, such as the requirement for maximum torque on hard acceleration, and the need for less engine drag during normal operation, for better fuel efficiency. Furthermore, they can closely manage the battery’s needs, for example by providing a higher charging rate at cold ambient temperatures. This helps to keep the battery in optimum states of charge and health.

Typically, the Engine Control Module (ECM) controls charging and can vary the charge rate dependent on a number of factors, such as ambient temperature (or battery ambient temperature), accelerator pedal position, electrical loading, and engine speed etc.

The alternator works at maximum capacity only when absolutely necessary. However, in the right conditions, such as after cold cranking in low ambient temperatures, the ECM can increase alternator output to 18 V. Therefore, it is essential that correctly specified batteries are used in these applications [Ford specified silver calcium batteries for their systems].

Conventional lead-acid batteries, which cannot handle high charging rates, are not a suitable alternative in smart charging systems.

Nowadays, smart charging systems are ubiquitous but Ford were the first to add the feature to mass market vehicles.

Smart charge alternators have a similar fundamental design as conventional alternators, with an electromagnetic rotor within stator windings, but their output is regulated by smart control of the rotors electromagnetic field: the ECM uses a Pulse Width Modulated (PWM) voltage signal to vary the rotor circuit current and, hence, its magnetic field strength. The higher its magnetic field, the higher the AC current induced in the stator windings and the higher the alternator’s rectified DC output.

A feedback signal is sent from the alternator to the ECM to provide a check the system is operating within tolerance. For this reason, smart charge systems [notably, the Ford system] can be highly intolerant to any alternator that is not manufactured to the original specifications.

If the smart alternator controller detects a system fault, the smart charging functionality will be disabled, Diagnostic Trouble Codes (DTCs) set, and the engine management and battery warning lights illuminated. Provided the fault is not within the alternator, it will still function conventionally with its output regulated to 14.75 V.

Other possible symptoms of faulty alternator or charging system might be:

• Rough idle.
• Possible engine misfire.
• Loss of battery state of charge or state of health.
• Erratic or malfunctioning dash board instrumentation.

Typical alternator, or related, faults are:

• Diode faults, caused by heat and vibration or the inclusion of moisture into the circuitry.
• Short or open circuits, or high resistances, in the stator windings.
• Poor battery states of health or charge.
• Short or open circuits, or high resistances, in battery or earth cables and/or connections.
• Alternator drive mechanism faults, including pulley, belt condition and tension, or freewheel issues.

GT141