Symptoms of overcharging an alternator

Written by paul novak
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Symptoms of overcharging an alternator
A faulty alternator (centre) will show various symptoms. (New car petrol engines image by Christopher Dodge from

A vehicle's alternator serves dual purposes in the proper operation of a vehicle's electrical system. A properly operating alternator will keep the vehicle's battery in a fully charged state, and it will supply additional electricity for the operation of the vehicle's accessories as it is needed. Although a weak alternator producing inadequate current is more commonplace, it is also possible for too much current to be produced.

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High Gauge Reading

An overcharging alternator will cause the voltmeter on the vehicle's dash to read an overly high voltage that may or may not vary with engine speed. Normal readings should be high upon start-up, then settle into the normal range. An overcharging alternator, however, will cause the meter to remain in the high position after initial start-up.

Low Battery Electrolyte

Low battery electrolyte levels are a sign the alternator is overcharging the battery and is a result of the heat generated from overcharging causing the electrolyte to evaporate. As the electrolyte is depleted, the battery's ability to hold an electrical charge diminishes, resulting in more heat and more electrolyte loss.

Burnt Bulbs

An overcharging alternator can lead to headlights and tail lights prematurely blowing out alone or in tandem. Other burnout symptoms of an overcharging alternator are repeated blown fuses, dash and interior lights blowing out and lights becoming extremely bright when engine speed increases.

Battery Heating

Overcharging of the battery by a defective or malfunctioning alternator will result in the battery reaching an overcharged state. When overcharged, the plates inside the battery shed material and lose their capacity to hold electricity. The battery resists further charging, and the excess electrical charge builds up and is radiated as heat. This has the effect of making the entire battery feel warm or hot to the touch after the engine has been running.

Swollen Battery

A battery being overcharged by a faulty alternator will create abnormal amounts of hydrogen gas. If the battery is poorly vented, or is a fully sealed type, this build-up of hydrogen gas can cause the sides or top of the battery to swell outwards, warping the battery's casing.

Seeping Battery

Seeping or leakage occurs when an alternator overcharges the vehicle's battery and hydrogen gas builds up within the battery, forcing electrolyte out of the battery through its vents or around the vent caps. In severe cases, the battery housing can become cracked or develop leaks, allowing the liquid electrolyte to leak out.

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