Charge Regulator

General

Fig 1: Charge Regulator

Courtesy of VOLVO CARS CORPORATION

The charge regulator is mounted at the rear edge of the generator (GEN). The role of the charge regulator is to constantly maintain the generator current at engine speeds, depending on the load and speed of the generator.

If the voltage produced exceeds the preset desired value depending on the load, the charge regulator reduces or cuts the magnetic current to the rotor. This, in turn, lowers the magnetic field. The voltage from the stator windings decreases. When the voltage is below the desired value, the current increases through the rotor so that magnetization increases as does the generator voltage until the desired value is exceeded again. This process is repeated continuously.

Charge voltage

Fig 2: Charge Regulator Graph

Courtesy of VOLVO CARS CORPORATION

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 overcome for charging to occur. At room temperature 0.2 V per cell or 1.2 V for the entire battery is required. 13.92 V (12.72 V+1.2 V) is required to charge a battery at room temperature. In cold weather conditions the chemical reactions are slower and the inner resistance becomes higher. This requires a greater voltage when charging to overcome the internal resistance.

The charge regulator controls the output voltage, depending on the engine compartment temperature, following a predetermined curve, see the illustration.

The charge regulator calculates the engine compartment temperature using integrated semi-conductor electronics. In cold conditions the charge regulator allows a higher voltage. At higher temperatures the voltage is lowered. This ensures full battery charging regardless of the temperature. A battery must have a greater charge voltage at lower temperature for charging to occur.

L-signal for the central electronic module (CEM)

Fig 3: Generator And CEM Input And Output Signals

Courtesy of VOLVO CARS CORPORATION

The charge regulator is connected to the central electronic module via an L-signal.

The L-signal is used to pre-magnetize the generator rotor and to transmit signals to the central electronic module telling the central electronic module that the generator is charging or not when the engine is running.

When the engine is starting, the generator (GEN) does not charge. When the engine speed (RPM) passes approximately 550 rpm a delay of approximately 3 seconds occurs. After the delay a successive increase of charging begins. When the generator (GEN) is at full load the increase ranges from 0-100% for a period of 6 seconds.

If the engine speed (RPM) passes approximately 1300 rpm during the delay or the successive increase breaks the increase, full charging is obtained immediately. This is to successively increase the load on the engine during the start-up phase and to ensure the engine starts.

If the L-signal is missing the generator will not start charging on start-up. Charge regulator can self magnetize the rotor and start charging in this way. This only happens at speeds in excess of approximately 2300 rpm. There is no successive charge engagement with self magnetization, the generator operates at full charge immediately.

DF-signal to the engine control module (ECM)