Can You Use A Larger Run Capacitor?

Image of Run capacitor source ACD Trade

Are you dealing with the run capacitor sizing dilemma? You are not alone. This is quite a common issue in the area of electricity and electronics. The primary function of a run capacitor is to ensure that the compressors not only start smoothly but also run efficiently.

In all the application areas, the size of the run capacitor will always depend on the specs of the motor. This means that different motors have different capacitor size requirements.

Everything will run smoothly when using a perfectly-sized capacitor. With a small-size capacitor, there is a chance that it will not have enough power to start the motor. What about using a large run capacitor? Well, things may not go on well as expected and read on to know more about this issue.

Overview of a run capacitor

We know that a capacitor is an electronic component used to store electric energy and releases it when needed. Capacitors are found in almost all electronic devices regardless of their sizes and applications.

Run capacitors are just like regular capacitors only that they are specifically designed for the AC motors. They have what it takes to improve the starting performance and smooth running of the motor.

A typical AC motor operates by rotating. A run capacitor ensures that there is a smooth shift in the way the motor is running. For example, how have you ever wondered why a motor will maintain a constant speed for a long period, or increase its speed at an instant action? It is all because of the electrical properties of the run capacitor.

How are run capacitors different from normal capacitors? The key difference is on how their ability to handle current and voltage. Run capacitors have the capacity to handle big variations of current and voltage.

What are the functions of a run capacitor?

A run capacitor has three key roles that it plays in the running and operation of induction motors. These functions include the following:

• Streamline the ripple voltage: If the motor is connected to a DC power supply, a capacitor will be needed to streamline the ripple voltage. Usually, ripple voltage is generated at the output rectifier and it has the AC waveform characteristics. A run capacitor will store the energy during the positive half-cycle and supply it to the motor during the negative cycle. The overall result is a smooth output which will be of higher voltage.
• Filtering the AC component from the circuit: As we have described above, the capacitor eliminates the AC characteristics from the circuit. This ends up ensuring that the output signal is smooth.
• Timing the circuit: Run capacitors can also function as circuit timers. This happens when the capacitors work in conjunction with the resistors so that you end up with a capacitor-resistor (CR) circuit. The timing performance in the circuit will depend on the values of capacitance and as well as resistance. Timing can be measured by the period taken by the capacitor to charge and discharge.

Run capacitor size rating

To know that you are using a large capacitor, you will first have to know its rating. Capacitor size is rated using the microfarads (µF) and is the SI unit that determines the capacitance value.

One farad can be equated to one-coulomb per volt. This value is too large and that is why most capacitors are measured. This explains why most capacitors used in most devices are rated by microfarads and picofarads.

Different run capacitors have different capacitance ratings. Some are large while others are small.

Also, each motor has power specifications that will define the size of the capacitor that you should use. The size of the capacitor needed to run a motor will depend on factors such as the required operating frequency, voltage, and power.

When do we say a run capacitor is large?

A run capacitor is considered large if its capacitance exceeds the motor’s specification. Let’s say your motor is rated 80 microfarads and you go ahead to use 200 microfarads run capacitor.

So, can use a larger run capacitor than the one that was used to run the motor?

The answer is Yes and No depending on other factors and parameters.

You can use a larger capacitor only if its MFD rating is higher than that of the previous capacitor by up to a maximum of 20%. If the capacitor runs within this range, you can be sure that the motor will run smoothly without suffering any damage. Also, the fact that new capacitors supply higher current means that it is likely to deliver better performance.

However, you need to be worried if the MFD of the run capacitor is more than 20% of the previous capacitor. The current being supplied to the motor will be way higher than what the motor was getting.

What are the dangers of using a larger run capacitor?

As we have said, you can use a large run capacitor on your circuit. The only limit is the capacitance should not be more than 20% of the rated motor capacitance.

What are the dangers of going beyond 20%?

The first issue is overcurrent. The capacitor will supply more electric current than what is needed to run the motor. This can easily lead to the overheating of the motor, something that will lead to mechanical issues.

Secondly, too much electric current than what is required can affect the efficiency of the motor. The fact that the motor will run at a higher speed than what is expected means that it will be impossible to predict its outcome. This can also affect the stability of the motor.

Can I use a lower run capacitor?

No, you cannot replace your run capacitor with one that has a lower power rating.

On the opposite side, using a smaller run capacitor will yield nothing. Even though the motor may start, it may not run smoothly as expected.

In fact, a lower-powered capacitor may fail to generate the magnetic field that is required to facilitate the running of the motor.

Buy high quality run capacitor

From this guide, it is advisable to buy the right capacitor that will meet the power rating of your motor. If it is larger than the previous one, the value should not exceed 20%. And if you are planning to buy run capacitors in China, ensure that you get them from reputable electronic components suppliers.

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