How the starting capacitor differs from the working one

Capacitors are passive electronic components and serve to accumulate and quickly release the accumulated charge.

They are polar, when the polarity must be strictly observed when connecting and if such connect the capacitor to the network with alternating voltage, then the polar capacitor will quickly heat up and explode. And not polar, which can be connected to the circuit, both with alternating voltage and constant voltage.

Capacitors are also actively used to start asynchronous motors in a single-phase network, and there they are starting and working. And what is the difference between them, let's figure it out.

Starting capacitor

So, let's start with the starting capacitor, and as the name itself suggests, such a capacitor is used only at the moment the motor starts. After the started engine reaches the set power and frequency, the starting capacitor is disconnected from operation.

Starting capacitors are used in certain types of motors and when necessary start a motor on the shaft of which there is any load that prevents free rotation shaft.

As can be seen from the diagram above, in order for the engine to start, we need to press the Kn1 button, which connects the capacitor C1 for the time that the engine needs to reach the operating parameters.

After that, the capacitor is turned off and the motor continues to rotate due to the phase shift in the working windings. It is important to take into account that the operating voltage of the capacitor C1 must be 1.15 times higher than the mains voltage.

That is, for example, for a single-phase home network, the normal voltage is 230 Volts, which means that the capacitor must have an operating voltage of at least 250 Volts.

Working capacitor

Now let's move on to looking at the working capacitor. So, the working capacitor is included in the circuit on a permanent basis, and it is designed to shift the phases of the motor windings.

In order for the motor to run stably, the capacitor parameters must be selected very carefully.

During operation, an increased voltage appears on the working capacitor, which exceeds the working one. Therefore, to ensure reliable and trouble-free operation, you need to use a capacitor with an operating voltage of 2.5-3 times more. That is, 500-600 volts. This will guarantee the required voltage margin during operation.

It is also extremely important for a working capacitor to choose the right capacitance and, depending on the type of connection of the windings (triangle or star), a calculation is made.

So, for example, you have a motor with star-connected windings. The calculation formula will be as follows:

If a 1 kW motor with a consumption current of 5 Amperes at a voltage of 220 Volts, then a capacitor will be required with a capacity:

4800 * 5/220 = 109 mF;

This means that the closest suitable capacitor will have a capacity of 110 mF.

When connected by a triangle, the formula looks like this:

This means that with the same network and motor parameters, with such a connection of the windings, a 65 mF capacitor is required.

Compare starting and operating capacitors

Now let's compare the starting and running capacitors and write it all down in table form.

This is all that I wanted to tell you about how the starting capacitor differs from the working one.

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