Let’s start with the inverter.
Even if you look up in Wikipedia, you will find only a few lines about this otherwise very useful device. Its very name suggests that something transduces, inverts (Latin inverto), people often call it a car inverter or a truck inverter. If we name it more explicitly, it will become clear what is inverted because its full name is a voltage inverter. You’ll also find it as a DC / AC converter in English texts. Thus we understand what it does as well: it converts the DC voltage, for instance in the battery, into AC voltage 220 V (50 Hz) in order to power different consumers working with mains voltage. These inverters are very popular at the beginning of the summer season, especially among people tempted by camping „in the wild“, i.e. at places where there is no power supply nearby. You just need a fairly powerful battery and an inverter with average power of approximately 400-500-600 W and you will be able to charge your laptop or watch a movie on your LED TV in the evening as well as enjoy an economic 3.5 W LED light.
Voltage inverters have modified and pure (full) sine wave as the latter are far more expensive. The modified (simplified) sine wave is good enough for ordinary domestic appliances, although the motor-driven devices will have higher noise level. The modified sine wave has a trapezoidal form of the voltage wave. The pure sine wave is required for measuring tools, medical equipment, telecommunication devices and laboratory equipment.
The right choice of inverter power causes most of the trouble. The problem is that we must know the type of load (consumers). If the majority of the consumers have a prevailing active ingredient of the load, we may choose an inverter with app. 20% power reserve. This means that the inverter must have a 1/5 higher power than the sum of the powers of all the appliances connected after it. However, if the load is reactive in nature (inductive or capacitive), the inverter must be 3 to 5 times more powerful than the devices connected in its output , otherwise it could be overloaded and its protection – activated. But how can we know the type of power of an electric coffee-grinder or a coffee-maker or for example of an electric shaver?
In fact, there are some simple reference points for non-professionals where you will not have to measure the power factor cos Ф. If the appliance that you connect is powered by an electric motor or has a transformer, it means that it has a reactive load and you need to multiply the power written on its cover by three. Therefore, the coffee-maker is an active load, and the grinder – inductive. The shaver is also an inductive load. The laptop is also powered through an adapter, which includes a transformer, but it is relatively small and will not significantly affect the calculation of the required power of the inverter. Practically every laptop could be fed through an inverter with 300W and higher power depending on the battery consumption in charge mode. Drills, pumps, screwdrivers, grinders, centrifuges, motor refrigerators, air-conditioners, etc. are all inductive.
Inverters have three types of power. Constant power, which can be maintained for a long period of time. Namely this power is assumed to be the rated power of the inverter and is written on it with large numbers. The second power is slightly higher than the first one ( about 20-30% ) and it can be supplied by each inverter for no more than half an hour, and the third one is peak (instantaneous) and is twice higher than the rated one, but it can last only a few milliseconds. It is also important because it serves to provide enough power in starting mode of electric motors or capacitive loads.