An alternator voltage regulator keeps the alternator’s output within a set range regardless of engine speed and electrical load. In most modern alternators it is combined with the brush holder.
What does it do?
By switching the rotor field current on and off, it holds output at roughly 13.8–14.6 V, preventing both undercharging at idle and overcharging at high rpm.
Types
- Mechanical (relay) regulators on older vehicles
- Integrated electronic regulators – most common today
- Smart LIN/BSS/PWM regulators controlled by the engine ECU
Failure signs
- Undercharging: warning light, flat battery, below 13 V
- Overcharging: above 15 V, blown bulbs, hot or swollen battery
- Lights brightening and dimming with engine speed
Smart regulators require dedicated testers such as MSG Equipment MS013, MS015 and MS016.
Frequently asked questions
Can a faulty regulator damage the battery?
Yes. Undercharging causes sulphation; overcharging causes heat, water loss and swelling.
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