If you plug in two wires of a three-phase electric motor, you will not get any effect other than a hum. At best, the motor shaft will jerk slightly. In order for it to start rotating, you need to include the electric motor in a single-phase network through phase-shifting capacitors. Moreover, it is necessary to use two capacitors (or their blocks) - a temporary starting, serving only for starting, and a permanent working one.
Necessary
- - three-phase electric motor;
- - metal-paper capacitors (MBGV, MBGO, MBPG, MBGCH);
- - electric wires;
- - tumblers;
- - insulating tape;
- - electrician's tool;
- - calculator.
Instructions
Step 1
Calculate the required capacity of the working capacitor. Its value depends on the type of connection of the motor winding. For a "star" connection, the capacitance is Cp = 2800 * I / U, for a "triangle" connection - Cp = 4800 * I / U, where Cp is the capacitance of the capacitor in μF, I is the current consumption in A, U is the mains voltage in V.
Step 2
Determine the current by the formula In = P / (1.73 * Un * η * COSφ), where P is the motor power in W, η is the efficiency (0.8-0.9), cosφ is the power factor equal to 0.85, U - mains voltage, 1.73 - coefficient characterizing the ratio between phase and line current. The capacity of the starting capacitor Cn should be 2-3 times (depending on the mechanical resistance at which the engine is started) to exceed the capacity Cp.
Step 3
If you do not want to engage in calculations, you can take the approximate capacitance values as follows: at P = 0.4 kW Cp = 40 μF, Cn = 80 μF; with P = 0.8 kW Cp = 80 μF, Cn = 160 μF; with P = 1.1 kW Cp = 100 μF, Cp = 200 μF; at P = 1.5 kW Cp = 150 μF, Cp = 250 μF; with P = 2.2 kW Cp = 230 μF, Cp = 300 μF.
Step 4
Purchase capacitors of the required power. Their rated voltage must be at least 1.5 times the mains voltage. For 220 V, it must be at least 500 V. Make a case (box) for capacitors of plastic or wood - so that they fit snugly into it. The case is needed so that the capacitors are a separate unit that can be located in a convenient place at a certain distance from the engine so that they are not exposed to vibration and mechanical stress during its operation.
Step 5
In the event that you have to collect the required capacity from several capacitors, connect them in parallel, i.e. assemble into a single block using two wires passed over the capacitors and soldered to their terminals.
Step 6
Connect the capacitors to the motor according to the diagrams shown in the figure (on the right for a motor whose windings are connected by a "delta", on the left - by a "star"). Cn and Cp denote the starting and working capacitors, respectively, P is a toggle switch that includes a starting capacitor in the circuit, P is a switch that changes the direction of rotation of the engine. When starting the engine, the P toggle switch must be on, after a set of revolutions - off.
