Common Overcharging Alternator Causes

By: Leon Rhodes

Vehicle Alternator

An alternator is designed to output slightly more voltage than a car battery is rated for. A typical 12 volt car battery, for example, requires an alternator output of 13 to 15 volts in order to keep the battery fully charged.

This is because the car's engine and electrical components(radio, gauges, lights etc) draw power when the engine is running. If the alternator in your vehicle's electrical system only generated 12 volts the battery would never remain fully charged.

It's also important to know that an alternator has an internal voltage regulator, a device designed to sense when your vehicle's electrical demand surges. During periods of high electrical demand, such as at night with headlights running, the voltage regulator will slightly increase alternator electrical output.

Do I need an alternator upgrade?

If you purchase and install high output aftermarket components, such as a heavy duty amplifier, winch or light bar, it is recommended that you consider upgrading your alternator. This is because the battery will drain more quickly causing increased electrical demand on your alternator.

Can I fix my alternator?

Typically a damaged alternator needs replacement but you can fix what caused it to fail. To fix a poor alternator ground connection check to make sure all wiring connections are clean, tight and secure. Make sure all wires are in good condition and that fuses are of the right amp rating.

How do I test my alternator?

With the key in the on position and the engine not running the volt gauge on your dash should read 12 volts. Start the car with all accessories turned off, if the alternator is working the volt gauge reading will rise to 13-15 volts. If your voltage gauge remains at 12 volts or lower the alternator is improperly connected, malfunctioning or unable to meet demand.

How to load test an alternator without removing it

Load test the alternator by turning on systems like the lights and air-conditioning while the vehicle is running. If the volt gauge on the dash reads 13-15 volts with a 12 volt battery installed the alternator is good. Use a multimeter to test the voltage at the battery if you suspect a broken dash voltage gauge.

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