How To Choose A Generator: Specialist Advice

In this article we have collected all the necessary minimum knowledge about generators, which will allow you not to make a mistake when choosing it.

Before proceeding with the choice of a generator, it is worth clearly deciding which parameters are most preferable for you. When buying a device, you need to consider its weight, dimensions, duration of operation, the availability of automation, noise level, fuel consumption, power and, of course, price.

How many phases should the generator have?

In order to answer this question it is necessary to understand which appliances will be connected to the electric generator. Only single-phase appliances can be connected to a single-phase generator. Three-phase generators can be connected both single-phase and three-phase. But this property does not mean that three-phase generators are always better. It must be remembered that for most generators the maximum permissible load in each phase should not exceed 30%. In practice, this means that you cannot remove more than one third of the rated power from a single-phase socket of a three-phase generator. Those. if the three-phase generator has a rated power of 6 kW, then you can remove no more than 2 kW from a 220 V outlet. Besides,

As a result, a three-phase station is best taken only when you have a three-phase consumer. If all appliances are single-phase, then in the vast majority of cases it is worth stopping at a single-phase generator.

How to calculate the required generator power?

Power is one of the main parameters that must be considered when looking for a generator to purchase. To determine the required power of the generator should check the power of the devices that will be connected to it. It should be borne in mind that the power of the generator should exceed the sum of the capacities of all devices connected simultaneously, which will work for more than five minutes, by 20-30%. This is due to the fact that the generator will operate in the most optimal mode only if the load connected to it does not exceed 40-80% of the rated power.

If the generator power is not selected correctly, then you will probably encounter:

• overload of the generator and its subsequent stop;
• reduced life due to prolonged operation at extreme conditions;
• high fuel consumption.

Choosing the right power, you will get the opportunity to connect to the network supplied by the generator not previously provided appliances.

Watts, Volt-Amps and Power Factor

Please note that power can be measured in watts (W) and volt-amperes (VA). If in the instructions for the device and in the instructions for the generator the power is indicated in different dimensions, then it is worth bringing both values ​​to a common unit of measurement. To convert kVA to kW, it is necessary to multiply the value in volt-amperes by the power factor (cos ȹ).

Suppose we have a generator with a capacity of 3 kVA and a power factor of 0.8; After making simple calculations, multiplying 3 by 0.8, we find out that the power of this installation is 2.4 kW. Now we calculate the vacuum cleaner of what power can be connected to it. Usually (cos ȹ) of a vacuum cleaner is about 0.5. Total, we calculate the power of the vacuum cleaner: 3 × 0.8 × 05 = 1.2 kW.

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And what should be the power of the heater, which can be connected to the generator described above? Since the heater does not have reactivity, its power factor is the same. Multiply: 3 kVA × 0.8 × 1 = 2.4 kW. That is, the power of the heater is the same as the power of the generator itself.

Resistive, inductive, capacitive …

For the correct selection of the generator, it is important to know the resistive, inductive or capacitive devices you intend to use. Resistive devices consume current with active power, simply those that do not have an electric motor. These include heating appliances, incandescent lamps, stoves. For this type of devices, any generator of the appropriate power is suitable, since they completely convert the power consumption into light or heat.

Inductive are devices that operate on an electric motor. For example, a compressor, pump or sawmill. This type is characterized by power loss due to friction of the winding; therefore, only 70% of the initial indicator is used as useful power. Also in inductive devices, additional power is required to start the engine. Therefore, when working with such devices, it is better to have a generator power reserve of about 20%.

If you buy a generator to connect inductive devices to it, you should definitely find out what maximum current it can withstand.

Capacitive devices are the most sensitive current appliances (for example, professional discharge lamps, flash lamps). To work with such devices use exclusively asynchronous generators.

Starting current

Inrush current is a current that occurs for a short period after starting equipment equipped with an electric motor. Starting current can be several times higher than the rated power of the unit. The value of this current can be found in the instrument manual. For approximate calculations, you can use the following table:

A little trick – if you connect the equipment not directly to the generator, but through a sufficiently thick and long extension cord wound into a coil (you need to wind the wire in turns, say, on a stick), then in this case the extension cord behaves like a choke (inductor having high resistance to alternating current) and inrush currents at the input to the generator are significantly reduced.

How to choose the right power?

Thus, when choosing a generator, you need to:

• determine which devices you will connect to the generator;
• determine the power of these devices (usually it can be read in the instructions or on the devices themselves);
• know inrush current coefficients for these devices;
• Based on the type of device and its power, calculate the required power of the unit.

If you are not able to know exactly what exactly the power of the devices you are going to connect, use the following table of approximate values:

A simple example of calculating generator power

A backup generator is needed to the cottage, so that when the lights are turned off once again for a couple of days, the refrigerator does not turn into a foul-smelling box of rotting vegetables and meat, and in the dark you could walk around the rooms without fear of injury. It would also be great to watch TV sometimes and vacuum the floor.

The total power of the devices listed by us will be approximately 1.5-2 kW. Let’s look at the type of load per power source (generator). To do this, look at the table of starting currents, and after that we calculate the required power for the above-mentioned simultaneously connected appliances of electricity (take the maximum values): 0.3 kW × 3.3 + 0.2 kW (two 100W lamps) × 1 + 0.08 kW × 1 + 0.8kW × 1.2 = 2.23kW . And since usually the maximum power of the generator (the power that it can produce for a short period of time) usually exceeds its rated power, for our purposes we can take a 2 kW generator with a light heart .

Fuel consumption

Want to determine fuel consumption for a generator? You need to know the generator power in kW. The flow rate in g / kW * hour multiplied by the generator power in kW gives the flow rate in g / hour. To get in liters / hour you need to know the specific gravity of the fuel in g / liter (for AI-95 (A-95) about 750 g / liter, for diesel fuel 840 g / liter), i.e., divide the rate in g / hour by density in g / liter. For example, petrol mileage 350 g / kW * h. Power generator 5 kW. Those. fuel consumption at full power – 350×5 = 1750 g / hour. Divide the resulting amount by the density of petrol (in our case AI-95) 750 g / liter and get 2.3 l / h.

In the exact calculation of the flow rate, it is also worth considering the change in fuel density with a change in external temperature. Tabular fuel density is indicated at the nominal temperature (20 degrees Celsius). The lower the temperature, the lower the density.

Synchronous and Asynchronous Generators

Synchronous generators – have a lower current quality compared to asynchronous ones, but, nevertheless, they are suitable for emergency power supply of offices, refrigeration units, equipment of country houses, cottages, construction sites. Such generators are more resistant to short-term overloads, but are poorly protected from water, dust and dirt because they draw air through them for cooling. The main advantage of such electric generators is that they pick up peak loads relatively painlessly. Those. for the operation of devices with a reactive load (having an electric motor), a generator of lower (compared to asynchronous) power is enough for you.

Asynchronous generators do not tolerate peak loads, but provide voltage maintenance with high accuracy, so they allow you to connect to them equipment that is sensitive to voltage surges (for example, medical equipment, computers, and other electronic devices). The source of electric current in them is the residual magnetization of the rotor. Thanks to this principle, asynchronous generators are more durable: they do not require air cooling and their case is completely closed and protected from moisture and dust. Due to their immunity to short circuits, such generators are an ideal source of power for welding machines. But they are sensitive to overloads and are not suitable for powering power tools and other devices with high inrush currents.

Which engine do you need?

The engine is the main part of the unit, how long the generator will last depends on its potential. Engines are petrol, diesel and petrol. The life of a petrol-powered air-cooled generator is approximately 500-800 hours for a Chinese petrol engine, up to 2,000 thousand hours for a Honda, Briggs & Stratton or Kohler engine. The resource of diesel engines significantly exceeds this indicator and ranges from 2500 hours for an air-cooled engine and 3000 rpm to 20000-30000 for liquid-cooled engines and 1500 rpm.

The resource of petrol engines is much higher than that of petrol engines and approximately the same as that of diesel engines. The resource of an air-cooled petrol engine is 1500-2000 hours for Chinese engines and about 3000-4000 thousand for Japanese, European and American engines. As for liquid cooling engines, their life starts from 10,000 engine hours for small displacement engines, up to 40,000-50,000 engine hours for large-volume engines.

Petrol engines are typically used on medium and low power generators. Cheap generator, low resource. This is a great option if electricity is seldom lost. Diesel engines are used for backup power supply of medium and high power. Pretty expensive generator with a good resource. Most often used in the construction or reserve of large objects. petrol are ideal for backup power supply of homes and industries. petrol generators are more expensive than petrol generators and cost about the same as diesel ones.

But unlike both of them, they have serious advantages: if there is a petrol main, the cost of 1 kW / h will be cheaper than petrol and diesel, which means that with intensive use the generator will pay off much faster. Besides, for petrol liquid-cooled generators, the cost of 1 kW / h (taking into account the cost of the station and the cost of its maintenance) is always lower than the cost of 1 kW / h from the city network.

And this is not to mention that the petrol engine is noticeably more environmentally friendly than both petrol and diesel. For example, when working on methane, the smell of exhaust gases is practically not felt and for a country house it is important.

Operation mode

Correctly determining the operating mode of the generator will allow the most efficient use of its resource.

All data presented in the table are approximate and do not apply to a specific generator.

Fuel safety

It is important to remember that long-term storage of petrol (more than 6 months) impairs its properties, which can lead to loss of power or even engine failure. Do not forget to change it every 3-4 months if you do not use the generator. Diesel fuel is more resistant to long-term storage.

Generator for garden

How to choose a generator for a summer residence? First of all, you need to decide what total power the appliances consume in your home. Above we calculated the minimum required power, for the “average” country house – 2 kW. But you do not want to calculate watts every time, but even limiting yourself, but use all the main electrical appliances at home. In practice, for a house in which 4 people live, the optimal generator power is 4-5 kW. It will be enough for basic household appliances at home (you can even forget that in the whole country house, no one except you has electricity).

Which is better, to save and take the device from China or still pay the necessary amount and buy a generator of European / Japanese production? The answer is not as obvious as it might seem at first glance. First of all, it depends on how often the generator will work. The engine resource of a modern Chinese-made generator is 1-1.5 thousand hours. If the electricity is turned off a couple of times a month for 6 hours, then you yourself can easily calculate that with such an intensity of operation, the resource will last for about 15 years. If for the foreseeable years a budget generator can easily meet your needs, is it worth overpaying for a better one ( and therefore expensive) brand? You decide, but I think there is not much point.

When can’t you save on a generator? First of all, when you plan to use it extremely intensively. For example, electricity is supplied only periodically and the generator will work for several hours every day. In this case, the quality of the generator, the reliability of its operation, fully pays off the money spent on it.

Generator for welding machine

The correct selection of the generator for the welding machine must take into account a huge amount of different data, such as maximum welding current, power, current curve, etc. of welding equipment. The starting currents of the welding machine are so aggressive and instantaneous that the fuses of the generator do not have time to melt and the alternator burns out. For simplicity and reliability, the generator power should be selected three times greater than the power of the welding machine. There is also a second way. Before connecting the welding machine to the generator, unscrew the welding current to a minimum and only then connect it to the generator. It should be borne in mind that the 5 kW generator is ready to withstand the welding current within 160A. An increase in current above this value increases the probability of generator failure.

Price-quality ratio

Planning a serious purchase always involves finding the best value for money. Today, high-quality units, a good assortment, the highest quality, but not very affordable prices are famous for electric generators produced in countries such as France, Germany, the USA and Japan ( SDMO , Endress , Generac ). This is a high quality and reliable equipment. But do not discount generators made in China. Some brands are close in quality and reliability to their European / Japanese / American counterparts (for example, Ergomax , Kipor , Huter), but at a price they cost two to three times cheaper. There are also brands that are between these two categories – for example, Russian-Chinese TCC or German-Chinese Fubag . The European production culture and quality components make their products the best in their class. Among petrol generators, in addition to Generac, Russian-made Gazvolt generators can be distinguished.

If we talk about specialization, it is better if it is a company that deals exclusively with the production of generator sets. Since this kind of business is highly specialized, do not count on the fact that you will be able to find the name of the company, which everyone is hearing. It is also worth considering that low-power units produced by branded companies can be unreasonably expensive. Make sure that the company manufacturing the generators has quality certificates and its products comply with international standards.

Before you buy an electric generator, think about how competent you are in this matter. If you are tormented by doubts – it is better to seek help from a specialist. If you know exactly what you want, take into account the device parameters you need, study the market and determine the price – do not forget to think about a possible repair in advance and carefully check the warranty documents when buying.