Major blackouts in recent years were wake-up calls for the everybody. A power interruption is more than spoiled food, loss of light or just an annoyance. It is a potential life-threatening situation, such as loss of air conditioning in the summer or heat in the winter, not to mention loss of power for electrically operated medical equipment.
A private backup power source lets you continue using selected appliances and lights during a blackout, or supply electricity to the entire house. An engine-driven electric generator (or a genset) is the most common and generally the least expensive type of backup electricity. However, among consumers there is a considerable lack of knowledge about available types, technical details, sizing requirements and safety of such devices.

This site is dedicated to practical information about various types of the generators for home use and for commercial applications. Before discussing their selection, let's quickly go over some basics. Generator is a Latin word that means maker or originator. In general, this term has various meanings. In power industry, it refers to a device that produces electricity, which is electric generator.


An electric generator is an electro-mechanical device that produces electricity from mechanical energy. Its operation is based on the process called electromagnetic induction: whenever a conductor moves relative to a magnetic field, electromotive force (emf) is induced in this conductor. Particularly, if a magnet is spinning inside a coil, a periodic AC voltage is induced between its terminals.


We know that although electricity does occur naturally, it does not exist in the forms that can be practically stored and utilized. Therefore for practical use electric energy is produced from other forms of energy, such as chemical, nuclear or thermal energy contained in various types of fuel. It can also be obtained from renewable resources. Electricity generation is a multi-step process. For eample, in the generators, the chemical energy stored in fuel is converted into mechanical energy of rotating shaft. A machine that does it is called prime mover. The common types of prime movers are steam turbines, internal-combustion engines, and gas combustion turbines. Electricity then is produced from rotational energy of the spinning shaft.
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In practice, the magnetic field is most often induced by an electromagnet rather than a permanent magnet. It consists of so-called field coils mounted on an iron core. A flow of current in the field coils produces magnetic field. This current may be obtained either from an external source or from the system's own armature. If it's obtained from the armature, the initial field is produced by residual magnetism in the electromagnet's cores. When the prime mover starts spinning, the armature at first operates in a very weak magnetic field and therefore produces small emf. This emf creates a current in field coils, which increases magnetic flux, which in turn increases emf. This process continues until the rated output voltage is reached.

When an external circuit connected to the coil terminals, the generated voltage will create an electric current resulting in energy being delivered to the load. Thus, the kinetic energy that spins the source of the magnetic field is converted into electricity. Note that the current flowing through an external load in turn creates a magnetic field that opposes the change in the flux of the coil, so the coil opposes the motion. The higher the load current, the larger the force that must be applied to keep the rotor from slowing down.

For more information see our tutorial on how generators work with an animation that illustrates their basic operation.


In power plants the electricity generating devices are most often driven by steam or hydraulic turbines or by diesel engines. The same concept of producing electricity is widely used in small consumer-grade units. In commercially available home generators, an alternator is integrated with an internal-combustion engine into a single assembly. Such an assembly called genset is the most common type of residential emergency backup power sources. A genset is often casually called just a generator even though it also includes an engine. There are two main types of such devices that differ by their connection and activation methods: fixed (standby) and portable. Fixed generators are permanently connected to both the building wiring system and a fuel line. Therefore they do require professional installation of a fuel line and a special redundancy system. The latter isolates the utility from your genset. Not surprisingly, permanent devices cost more than portables. However, they have a big advantage-- they can provide practically continuous power for as long as the fuel is supplied. Portable models are intended primarily for a temporary connection to several appliances via extension cords rather than to the whole house. They are normally powered from an on-board tank and therefore need frequent refueling, although some more expensive models can also be connected to an external source for longer operation. A portable unit is generally cheaper than a standby and can be used without any professional installation. However, if you want to connect it to the house wiring you still need to install a transfer switch. Choosing the best device for your application involves selecting the right type, choosing the fuel, and a proper sizing based on the amount of power you may need during an emergency.


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