ALFA IN - development, production, sale and service of Professional Power Generators MEDVED

How to correctly choose MEDVEDA (power generator)


What you need to know for the right choice of power plant.


1. 1 x230V, 3 x 400V or cardan

You need to answer the question of what you will primarily use the generator for, whether it is sufficient

  • single-phase power plant 1x230V,
  • or it will occasionally be necessary to power three-phase appliances 3x400V
  • or the primary job is to weld.

But there’s one more question you can’t ask most of the competition. Do I need it with a motor? Do you need to have an engine or tractor in your fleet that is equipped with a cardan output? If so, M-Watt is the clear choice!

2. What regulation will you need?

If you want to choose the power of the central unit correctly, we need to know quite precisely the input power of your appliance and the type of appliance, especially in terms of requirements for supply voltage fluctuations and the nature of changes in the load of the generator (current surges during start-up or sudden changes in input power during operation).

2.1. AVR regulation If it is an appliance that you know is sensitive to voltage fluctuations (e.g. computer, sensitive medical devices, tools with electronic control of input voltage), you need to choose the type of output voltage regulation of the power plant very carefully here. You will use a generator with an AVR. It is an electronic regulation of the output voltage, which ensures that the fluctuation of the output voltage will be within a tolerance of ± 2% in the entire range (at constant load) up to the nominal power of the generator. (AVR is not needed for PEGAS or ALFIN welding machines with PFC – power factor correction, which are not susceptible to voltage fluctuations, but it is necessary to count on a power reserve of power plants of at least 30%).

2.2. Compound CCL regulation If you need to “spin” an asynchronous motor on a circular saw, a paving cutter, or a compressor, i.e., a device with a difficult start-up, you definitely choose a power generator with a compound transformer. These motors do indeed have a “HARD START”, but the compound transformer ensures that the central unit is able to supply a large starting current, even at the expense of the voltage drop. A lower voltage will not harm the asynchronous motor in any way. Calculate that for your “one kilowatt” motor you need 2 – 4 times its rated power in the short term. PEGAS or ALFIN inverter welding machines with PFC – power factor correction – can be operated without problems on power plants with a compound transformer.

2.3. CCL capacity regulation The last series of appliances are manual tools with commutator motors, for which the output voltage with capacitive regulation is sufficient. The power consumption of the appliance can be up to the maximum rated power of the power plant.

3. Possibilities of protection against dangerous contact with inanimate parts

3.1. Standard The safety of the device due to the possibility of electric shock is ensured by separation – the winding of the alternator is not connected to the ground. 3.2. Optional accessories (electrical switchboard, safety elements, circuit breaker) The current protector ensures safe operation and protects the operator in the event of insulation damage. The RCD disconnects the electrical circuit in the event of a difference in electrical current between the power output of the alternator and the part of the circuit connected to ground behind the RCD output. It is prohibited to connect PE and N onto PEN!!!

4. Selection according to performance and type of powered device

The coefficient determines the approximate multiple of the increase in the “label” power consumption of powered devices, which may occur for a short time during operation, especially during the start-up of the device. Most devices have a coefficient of 1, with the exception of those listed below (the list is not complete, it is only an example).

3Pressure washers
 3.5 – 5Refrigerator
2.5Concrete mixers, manual angle grinders, circular saws
2Machine tools and electric grinders
3Submersible pumps
4Washing machines
3,5 – 5
1.5Taladros, fresadoras, Luces halógenas y fluorescentes
2Shredders, string trimmers, brush cutters, hedge trimmers, mowers and chain saws
The coefficient by which it is necessary to recalculate the required power of the power plant

We will be happy to advise you when choosing a power generator. Alternatively, we will come to test the selected types, as in some cases the correct performance is difficult to determine from the table. These are mainly compressors, complexes with multiple powered devices, servers with UPS, cooling boxes, etc. These are mostly 400V and power from 9-10 kVA and above. In these cases, in agreement with the merchant, the manufacturer ALFA IN a.s. arrives at the agreed date directly to the customer with several types of generators and performs a physical test. For this test, it is necessary for the customer to provide their own worker responsible for connecting the resources. This worker must have the appropriate authorization to enter the customer’s electrical network. The manufacturer will supply generators and a technician to operate them for testing. However, he does not have the right to interfere with the electrical installation. In the Czech Republic and Slovakia, we perform these performance tests approximately 1-2 weeks after the first contact.

If the above conditions are met, the manufacturer ALFA IN a.s. make tests free of charge and without obligation as a service to the customer.