Charge regulator (Alternator control module (ACM))

General

Fig 1: Identifying Charge Regulator

Courtesy of VOLVO CARS OF NORTH AMERICA.

For B8444S

Fig 2: Identifying Charge Regulator Bracket & Connector

Courtesy of VOLVO CARS OF NORTH AMERICA.

The generator (GEN) has an inbuilt charge regulator at the rear (also known as the alternator control module (ACM)). The regulator can be replaced. The carbon brushes are integrated on the slip rings on the rotor on the regulator.

Charge voltage

At room temperature a fully charged battery cell produces 2.12 V. A 12 V battery has 6 cells and therefore produces 12.72 V when the battery is fully charged. The battery has an internal resistance which must be exceeded before charging can take place. At room temperature 0.2 V is required per cell, or 1.2 V for the entire battery. Therefore to charge a battery at room temperature, 13.92 V (12.72 V+1.2 V) is required. In cold conditions, the chemical reactions take place at a slower rate and the internal resistance increases. This requires a higher voltage during charging to exceed the internal resistance. The charge regulator, depending on how it is controlled by the central electronic module (CEM), regulates the output voltage so that the battery receives optimal charge.

If the charge regulator is connected to the engine control module (ECM), it will use the commands from the engine control module (ECM) and central electronic module (CEM) to regulate output voltage so that the battery is charged optimally.

Charge regulator control

Fig 3: Identifying ACM To CEM Communication Link

Courtesy of VOLVO CARS OF NORTH AMERICA.

Fig 4: Identifying ACM, ECM & CEM Communication Link

Courtesy of VOLVO CARS OF NORTH AMERICA.

The above illustrations depict the two different types of connections for the alternator's regulator.

Depending on the model year and type of engine management system, the charge regulator (also known as the alternator control module (ACM)) is connected to either the central electronic module (CEM) or the engine control module (ECM). It communicates via LIN communication. For information on connection, see the illustration above and the wiring diagram.

If the charge regulator is connected to the engine control module (ECM), the engine control module (ECM) then communicates with the central electronic module (CEM) regarding alternator control via the controller area network (CAN).

The central electronic module (CEM) has built-in functions for regulating voltage level and current consumption in the vehicle. The central electronic module (CEM) controls the charge regulator either directly or via the engine control module (ECM). In this manner, it also controls the current/voltage produced by the alternator.

The generator does not initially charge when the engine is started. The charge increases successively when the engine has been started. When there is an increase in load at the generator, the increase from 0 - 100% takes place over the course of a few seconds (this time varies slightly depending on the operating mode the engine management system is in). This is to gradually increase the load on the engine during the start-up phase and to ensure the engine starts.

If the engine speed (RPM) exceeds idle speed (the exact engine speed varies slightly depending on the mode the engine management system is in) during this delay, or if the progressive increase is interrupted, full charge is obtained immediately.

If there is no communication with the charge regulator, the charge regulator will not start charging on start-up. The charge regulator can however self magnetize the rotor and start charging. This occurs at engine speeds greater than approximately 2100 rpm. There is no charge engagement by stages with self magnetization, the generator operates at full charge immediately.

When self magnetizing has begun, the generator (GEN) also charges at engine speeds below 2100 rpm.