Help Choosing an Alternator For Your Generator

The alternator shaft, often called the rotor because it rotates, is usually supported by two bearings. This is called a double-bearing alternator because there are two bearings.

When the rotor is directly coupled to the prime mover (internal combustion engine, gas turbine, water turbine, etc) it may rely on the prime mover’s end bearing to support its weight and allow it to turn smoothly. This configuration eliminates one bearing on the alternator shaft and such an arrangement is called a single-bearing alternator.

Engines and alternators use SAE standard sizes for the flywheel, flywheel housings and hole dimensions. You will need to determine what SAE Housing and SAE flywheel adapter you have. Use the guide below to find out what you need. Engines can be purchased with different size flywheels and housings so your engine maybe totally different from the same engine model used by someone else.

Here is a great resource for calculating pulley sizes, speed and belt lengths.

https://www.blocklayer.com/pulley-belteng.aspx

For most applications, an alternator with a 4-wire output (dedicated wiring) is the most efficient and least expensive. Another option is a 12-wire alternator. Twelve wire alternators can be reconfigured as shown in the wiring diagram below. There are terminals on the top of the alternator with labeled wires from the coils connected to them. You can reconfigure them by following the diagram to produce different results.