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.
