Correct selection of the operating capacitor of the electric motor

When a three-phase asynchronous motor is connected to a 220V network, its power is lost; in addition, it does not start without a phase shift. To compensate for the difference between 380V and 220V, electric motors are connected using capacitors. The quality of the engine and its performance depend on how correctly they are selected.

What you will need:

• working capacitors of different ratings;
  
• ammeter or voltmeter.

The process of selecting working capacitors

There is a rule according to which for every 100 W of electric motor power there should be 6.6 μF of the working capacitor capacity. This is a very approximate value that requires adjustment depending on how the motor is connected to a single-phase network. Much more accurately, the optimal capacitance of a capacitor is determined in practice. In addition, the motor may not have a tag indicating the power, then it is impossible to find out what capacitor capacity it needs based on a given proportion.


In practice, regardless of whether the motor is connected in a star or delta configuration, you can determine the optimal capacity by connecting an ammeter or voltmeter to it. When using an ammeter, it is connected to any of the supply wires. Next, capacitors of different capacities from small to large are installed one by one. Ammeter readings are taken at each of them. On which capacitor they are the lowest, the one that fits best.

When using a voltmeter, the complexity of measurements increases. Readings are taken on different capacitors. On each of them, a measurement is made between the direct 220V contacts and the capacitor. The optimal option would be one in which both indicators are approximately the same.

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