## Why is alternator voltage higher than battery voltage?

When engine is running, the alternator output is greater than the battery voltage, so current flows from the alternator to the vehicle loads as well as the battery. This implies that alternator output voltage must always be above the battery voltage during operation of the engine.

## How many volts does an alternator output?

Normal Output An alternator should put out between 13.5 and 15 volts of power. The alternator should be tested with the engine idling and electrical accessories, such as the radio and headlights, turned off.

How many volts should an alternator put out at idle?

Most alternators that are charging properly should produce a voltage of about 13.8 to 14.2 volts at idle with the lights and accessories off.

Is 14.8 volts too high?

Low maintenance batteries 13.2-14.7V is normal. 14.8V is considered overcharging. A bad regulator over charging would most like shoot upwards of 16.0V. State of charge, temperature, age of batteries all have an effect on the charging rate.

### What causes an alternator to output low volts?

If the voltage at the battery and alternator don’t match. For example the battery reads 12v and alternator reads 14v. This means that there is an issue with wiring. While applying the same conditions as above.

### What does it mean when battery and alternator don’t match?

Also the voltage at the battery and the voltage at the alternator should be within 0.5v of each other. If the voltage at the battery and alternator don’t match. For example the battery reads 12v and alternator reads 14v. This means that there is an issue with wiring. While applying the same conditions as above.

What is the voltage of an alternator rated at?

The last number is 13.5V, which is “VT” or the voltage that the alternator was held at during the test. Since an alternator’s output can vary both up and down from 13.5V in real-world situations, it’s actual output limits will vary from the idle and rated numbers.

When does the alternator light turn on the battery?

On older vehicles, the battery light would turn on the alternator light when the alternator output or battery voltage dropped below a preset value. The battery light on modern vehicles, however, is controlled by data and trouble codes. This is why a scan tool is essential to diagnosing a charging system.

#### What’s the difference between battery voltage and alternator voltage?

Using a voltmeter to check for voltage drops across connections can reveal bad connections that may reduce the charging voltage. The actual output voltage produced by the alternator will vary depending on temperature and load, and will usually be about 1.5 to 2 volts higher than battery voltage.

If the voltage at the battery and alternator don’t match. For example the battery reads 12v and alternator reads 14v. This means that there is an issue with wiring. While applying the same conditions as above.

#### What is the voltage of an alternator at idle?

The actual output voltage produced by the alternator will vary depending on temperature and load, and will usually be about 1.5 to 2 volts higher than battery voltage. At idle, most charging systems produce 13.8 to 15.3 volts with no lights or accessories on.

Is it normal for an alternator to not charge?

Still, it’s perfectly normal for others to see the alternator not charge at all intermittently. One test is not enough if you are diagnosing a charging system problem. All too often, the alternator is condemned as the source of the problem if only battery voltage is present with the engine running.