When talking about a portable generator, people usually mean the fossil fuel-powered generators that are mobile. 

A conventional portable generator is in its basic sense a fuel-powered engine with an alternator that has an electrical output. The three most common fuel types used for portable generators is gasoline, diesel and propane.

Some portable generators are hybrids. This means that the engine can run on more than one type of fuel – usually a combination of gasoline and propane.

The engine speed and the corresponding electrical output is the key characteristic of a conventional portable generator. A conventional fuel-powered portable generator is meant to run 3600 rpm to generate 120 volts and a frequency of 60 Hertz.

However, one of the main disadvantages of most fuel-powered portable generators is that the machine cannot maintain a steady 3600 rpm. This means, that the voltage and Hertz also fluctuates.

The fluctuations are referred to as harmonic distortion. The constant changes in electrical output or high harmonic distortion is why fuel-powered portable generators don’t provide what is called ‘clean electricity’.

Clean energy is preferred for electrical devices that are sensitive like laptops, DSLR cameras, mobile phones etc. Not being able to hold steady at 3600 rpm is also the reason why fuel-powered portable generators are so noisy.

With fuel-powered portable generators there is a correlation between its fuel tank, power and run time. In most cases, the bigger the fuel tank, the more power and the longer the run time.

Since some portable generators can produce upwards of 10,000 watts of power, you can imagine that these are quite large and heavy generators. Despite their size and weight, most models are still portable – most conventional portable generator models have wheels and a handle.