Speed of Alternators

Keeping a vehicle running is the job of the charging system. Many components make up this system, including the alternator. For a properly functioning alternator, the correct speed of its rotor must be adjusted.

Function

An alternator provides the electrical energy to keep the car's battery charged, as well as powering all other electrical portions of the vehicle. The amount of electrical energy yielded is related to its rotor rotation speed.

Features

The speed of the alternator is determined by an equation. Divide the crankshaft pulley diameter by the alternator pulley diameter. This gives the overall ratio. Then, multiply the pulley ratio by the engine speed to determine the revolutions per minute (rpm) of the alternator.

Considerations

Keep in mind that the alternator speed does not necessarily equal the engine speed. Ratios vary depending on the driving conditions. For normal, everyday driving, a 3:1 pulley ratio is sufficient. In contrast, racing on a circular track requires a 1:1 ratio.

References

• AA1 Car: Alternator & Charging System Checks
• Motor City Remanufacturing: Technical Information