The alternator is crucial in automotive technology, and the smart charge alternator represents a significant advancement in this field. It offers improved efficiency and performance. smart charging technology allow manufacturers to increase fuel efficiency. This is important due to Corporate Average Fuel Economy (CAFE) regulations that penalize inefficient vehicles. These regulations have become stricter in the last decade to promote domestic employment and combat global warming. This is important because since 1975, Corporate Average Fuel Economy (CAFE) regulations have indirectly driven innovation in the automotive industry.
General Operation
Variable voltage output generators are controlled by an ECU instead of a regulator internal to the generator. The main goal of these systems is to reduce the electrical and mechanical load, thus increasing fuel efficiency.
Smart charging technology has become the industry standard in modern vehicles. These systems consist of different components, such as a battery sensor that measures voltage and amperage, and the PCM/BCM. Interprets data PIDs like ambient and coolant temperature, engine RPM, and battery temperature to calculate state of charge. Manufacturers may use various strategies to optimize fuel efficiency, with some employing multiple charging systems.
Practical Example
It’s common for vehicles to have an alternator voltage output close to the battery voltage at idle. When heavy loads are turned on, such as the HVAC system, headlights, or stereo, the alternator will output 13V or more. This type of system was used by Honda/Acura from 1990 to 2012.
Honda Dual Charging
Let’s look at the Honda/Acura dual-mode charging strategy, which includes high and low output modes. The high output (normal) mode has a voltage of 13.5-14.9V, while the low mode is 12.5-12.7 volts. This dual-charging strategy can reduce engine load by as much as 10%, and it is accomplished by all the information gathered from the Electric Load Detector and various other sensors. The parameters required for low output mode are electrical load below 15 Amps (varies with the vehicle), vehicle speed between 10-45 mph or at idle while in drive, engine speed below 3,000 rpm, coolant temperature above 167°F (75°C), A/C Switch Off, intake air temperature above 68°F (20°C).
High output mode is meant for when the exterior lights, HVAC system, and entertainment system are on or when more than one data PID indicates a heavy electrical load requirement.
The Electric Load Detector, located inside the under-hood fuse box, is the single component that makes the Honda and Acura charging system one of a kind. Its main job is to monitor the amount of electrical energy the vehicle is consuming and then relay this information back to the ECM by pulling a 5V reference to ground as the load increases. This tells the ECM to increase or decrease the field strength in the alternator. At the ELD terminal, it is normal to find 2-4 volts when in low mode and 1-2 volts on the reference circuit when in high output mode. The ELD has a typical range of .27V up to 4.56V; anything outside these parameters will cause the ECM to trigger a DTC.
High Output Mode
Honda’s Newest Charging System
Honda in 2012 began using a different charging strategy called EMS (Engine Management System).
A quick rundown of this system’s operation:
- PCM commanded setpoint voltage
- Regulator with bi-directional LIN Communications
- Receives PCM setpoint, Soft Start (SS) and Load Response Control (LRC) commands
- Transmits alternator load and diagnostic information
- PCM monitored the current demand for vehicle through the ELD
- PCM monitored battery SOC
- PCM Commanded Battery Lamp
Don’t assume the charging system is faulty just because the alternator shows 12.5-12.8V at idle. Check for a shunt on the battery post terminals or a current sensor. Consider when the vehicle was manufactured and, most importantly, find accurate service information to better understand how the charging system operates. Smart charging technology is now an industry standard, even on base trim levels, helping automakers meet CAFE regulations. Remember to diagnose and never guess.
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