Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Charge Regulator (Alternator Control Module (ACM))
General
For B8444S
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
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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