What Is a Alternator?
The alternator is an AC generator driven by a belt from the engine crankshaft pulley. It converts mechanical energy from the engine into electrical energy — typically producing 13.5 to 14.8 volts — which recharges the battery and powers all vehicle electrical systems while the engine is running. Inside the alternator, a rotating electromagnetic field (rotor) induces alternating current in stationary windings (stator), which is then rectified to DC by a diode bridge. The voltage regulator maintains output within the correct range.
What Does the Alternator Do?
The alternator is the vehicle primary electrical power source during engine operation. Without a functioning alternator, the battery would be depleted within 30 to 60 minutes of engine running as all electrical consumers drain it. The alternator must produce sufficient current to simultaneously power all active electrical consumers while still charging the battery. High-output alternators are required on vehicles with many electrical consumers.
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Get My Free Fault Scan →Symptoms of a Failing Alternator
Alternator failure causes the battery warning light to illuminate, progressive voltage drop affecting all electrical systems, dimming headlights, malfunctioning electrical components and ultimately failure to start as the battery is depleted. A failing alternator diode can cause a clicking noise from the stereo speakers and flatten the battery overnight due to battery drain.
When Should the Alternator Be Replaced?
Alternators are replaced on failure. The auxiliary drive belt and tensioner should always be replaced simultaneously. Typical alternator replacement costs range from £180 to £400 at an independent garage.
If you are experiencing symptoms related to your alternator and are unsure whether it needs replacing, a free MotorLoom fault scan can help identify whether the component is likely at fault - giving you the most likely cause and estimated repair cost before you visit a garage.
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Related Parts
Other components that work alongside or are related to the alternator: