Uncle Bobs Tips: Generator Guide

Types of Generators

There are two types of generators: stand-by generators and prime power or portable generators.

There are two basic types of electric power generators: stand-by generators and prime power or portable generators. Stand-by sets are used as a backup to normal utility power, i.e. during an electric blackout. Hospitals, communications service installations, pumping stations and many other facilities are equipped with standby power generators. Stand-by generators are permanently hardwired into a building's electrical system and often get fuel from city gas or propane lines.

Prime power/portable generators on the other hand, are used where there is no alternative source of power, i.e. to supply power tools at construction sites or to power lighting or amusement rides for traveling carnivals. Built-in fuel tanks allow them to run anywhere. They may also be used to power essential equipment during a power outage like stand-by generators, however unlike stand-by sets, they are designed to be used for only short periods of a few hours at a time. As a result, they tend to be much smaller and less expensive.

All power generators are composed of two main components: A motor (engine) that burns fuel to supply power (usually propane, natural gas, gasoline or diesel), and a power generator head that turns that power into electricity. Together, the motor and the power generator head comprise a standard generator. In addition to the engine and generator, engine-generators generally include a fuel tank, an engine speed regulator and a generator voltage regulator. Many units are equipped with a battery and electric starter. Stand-by power generating units include an automatic starting system and a transfer switch to disconnect the load from the utility power source and connect it to the generator.

Generators are also categorized in terms of their forms of use. Generator manufacturers offer the following classes of generators: residential/home use, recreation and trailer, construction, rental, emergency and military.

Available in a wide range of power ratings, electric generators produce either single or three phase power. Single-phase electric generators are set up to produce 120 or 120/240 volts while three-phase electric generators produce 120/208 or 277/480 volts. Most homeowners will require single phase; industrial or commercial applications usually require three phase power. Hence, power generators range from small, hand-portable units that can supply several hundred watts of power, to cart mounted units that can supply several thousand watts, to stationary or trailer-mounted units that can supply over a million watts.


Most generator engines/motors operate at one of two speeds: 1800 RPM or 3600 RPM. 1800 RPM, four pole sets are the most common and least expensive. They last longer and run quieter. 3600 RPM, two pole sets are smaller and lightweight, and are best suited for portable, light-duty applications.

As any motor, a generator motor creates quite a bit of heat and needs a cooling system to prevent overheating. Standby generators can be either air-cooled or liquid-cooled. Air-cooled systems are louder and not quite as effective. Liquid cooled systems are quieter and more dependable - and also more expensive to purchase and to maintain. Large generators are typically liquid-cooled, 1800 RPM units, which give the best combination of quiet operation and reliability. Portable generators are almost always air-cooled, 3600 RPM models.

It's important to note that generator manufacturers don't actually build their own motors. They use engines from well-established names such as Ford, GM, and Honda to power their generator heads. Thus, when choosing a generator, look for one that comes with a brand name motor for which it will be easier to find parts and service than for no-name models

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