Author: Clare Johnson

Electric Generator Purchasing Guide

Power generators are not all the same. Each model has peculiarities and characteristics that must be well examined before proceeding with the purchase. You have to take the one calibrated to your needs, suitable for the components that we will have to power. Specifications include rotational speed, efficiency, fuel type, waveform of the current generated, frequency stability, noise levels, starting type, and overload characteristics. Below is a guide to the advantages, disadvantages, and features that every portable power generator has. One of the best is 12000 watt portable generator with electric start.

Rotation Speed and Inverter

Normally 60 Hz generators operate at speeds between 1800 and 3600 rpm (revolutions per minute). The corresponding speed for 50 Hz generators is between 1500 and 3000. The 3600 rpm units have two poles and are simpler to build and therefore have a lower purchase cost. The 1800 RPM generators are 4-pole machines and are a bit more expensive, but we are talking about bigger sizes here. In general, the higher the RPM, the more wear there will be on the bearings, which means more frequent maintenance.

Two-pole generators are therefore more cost-effective for use in relatively light applications that require less than 400 hours of operation per year. Some generators have a built-in inverter. The advantage is that the load on the inverter determines the amount of mechanical energy required to meet the electrical load requirements. As a result, the generator is controlled to run on a variable motor by accelerating the maximum motor power when required. This reduces fuel consumption at low load levels and, as a result, increases the overall efficiency of the generator. In addition, these models tend to be quieter.

Fuel for use in the Current Generator

The choice of the right generator based on the fuel used to power it will depend on several factors. Although diesel generators tend to be more efficient and consume less, diesel fuel is sometimes more difficult to find and is more likely to be contaminated with water or other liquid components. At low temperatures, diesel engines tend to have a more difficult start, so they need to be used under properly controlled temperature conditions if they are to be started and stopped.

Petrol engines are the easiest to find and also to use. They start easily and work even in adverse conditions. There are also generators that use propane gas. Be careful if we use the generators at altitude. Unless otherwise specified in the label for generators it is reasonable to downgrade the efficiency of gasoline, diesel and propane generators by 3% every 1000 feet above sea level, approximately 330 meters.


Electrical and mechanical losses are present in all generators. However, the greatest losses are attributable to the motor. Each generator has a particular load at which it operates with maximum efficiency, which usually corresponds to 80%-90% of the full rated load (see graph above). It is therefore important to buy the generator that delivers the right power according to your needs and not buy one that works at 50% of its capacity, as we will lose efficiency.

For systems with highly variable electrical loads, it is particularly inefficient to use a generator unless you use it to recharge batteries that will then power the electrical consumers.

Frequency stability

Depending on load requirements and if the generator is connected to AC loads with critical power frequency requirements, frequency stability may be a necessary parameter to consider. It is generally desirable to maintain frequency fluctuations of less than ± 0.5 Hz for AC loads. Conventional generators often have a specified frequency stability of 5%.

Noise Level

Some generators are noisy and others less so. If we use it outdoors we check what the local ordinances say about noise, whether we are above or below the threshold allowed for use. The noise level is specified in db, decibels, the higher the noise produced, obviously proportional to the power. There are also silenced current generators to reduce the output noise.

The overload

A synchronous generator can suffer serious consequences in case of overload. This can happen during normal operation or when it is switched on. If we use the generator as an electric motor, the starting current of the motor can place the generator in an overload condition that can cause the generator to slow down and possibly damage the motor.

The choice

If we don’t have to use the generator often, a small, portable one may be enough. If it is to be an essential and reliable component of our energy system, capable of operating for long periods and for a significant number of hours a year, a fixed unit is preferable.

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