happens that there's a good little machine, drilling machine or lathe, powered by 380 volts.It could be set in the home workshop or at the cottage.But the trouble, in these areas there is only ordinary sockets.
In cases where you need to connect a three-phase motor and is only available single-phase voltage source, out of the situation is possible, powering one of the windings through the phase-shifting element - the starting capacitor.So it is possible to receive a replacement third shifted by 120 degrees phase voltage.
Ideally, the motor is required to accelerate a large capacitance value, and upon reaching the nominal angular velocity - another, smaller.To achieve this, apply a scheme that allows to disable the excess capacity in both manual and automatic mode, leaving only its working value.
In the case of the winding connected to the star, the working capacity of the run capacitor is determined by the formula:
Cp = 2800 (I / U)
In the case of the delta dependence on each:
Cp = 4800 (I / U)
However, the connection of the motor windings triangle is undesirable, because in this case, an AC voltage must be 380 volts on each of them, and in the home network - only 220.
For ease of calculating the value of capacitance of the capacitor can be used formula according to which
Average= P / 10,
C = P / 5,
where P - power, W;
C - capacitance of the capacitor inrush, MF;
C - capacitance of the capacitor starting, Matt.
Thus, the capacity of the starting capacitor must be a half to two and a half times longer working.
standard voltage AC 220 volts.The question arises of how to determine the current value appearing in the above formula.
It's easy.Rated power of the motor is known, it is listed on the label attached to his body, and he serves as a kind of passport.
I = P / (1,73 U cos φ),
where
I - the amount of current ampere;
U - voltage (220 V);
φ - phase angle.
correctly calculate and pick the starting capacitor for electric motor, can be connected to single-phase supply practically all types of three-phase motors.Some will work better, that is, their characteristics will be more close to the passport during their regular inclusion (for example, a series of AOL, UAD, APN).Series MA, characterized in that their structure is applied shows a double squirrel-cage rotor will display inferior results.
choosing the starting capacitor should consider the fact that at the start of any current values that significantly exceed the nominal value.Thus, it should be remembered that the conductor cross-section, providing power to the motor, must be chosen with a margin.
now about what the starting capacitor can be used to connect a three-phase motor in single phase.Electrolytic tank can be used, but the presence in the circuit rectifier diodes complicate it and lower the overall reliability of the entire system.Even Henry Ford rightly argued that the smaller parts, the lower the chance of breakage.
easier and safer to install a paper capacitor inrush.Voltage indicated on the package, it should be less than 220 volts.
