Exploring the Differences Between Start Capacitors and Run Capacitors

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What is a Start Capacitor?

A Start Capacitor is a type of capacitor that is used to start an electric motor. Usually, a centrifugal switch is used to connect it in series with the motor windings. The centrifugal switch is open and the motor windings are connected to the Start Capacitor when the motor is started. The motor receives a sudden energy boost from the Start Capacitor, which aids in overcoming the torque during startup. The centrifugal switch closes after the motor starts, severing the Start Capacitor's connection to the motor windings.

Exploring the Differences Between Start Capacitors and Run Capacitors - Blog - Ampheo

How to Identify Start Capacitor?

Start Capacitors usually have a plastic casing that is either black or blue and has a cylindrical shape. Additionally, the capacitance value in microfarads (uF) and the voltage rating in volts (V) are usually labeled on them. You can test a Start Capacitor by measuring its capacitance with a multimeter. A rated capacitor's capacitance should be within that range. The capacitor needs to be changed if the capacitance is less than the specified amount. Another method for testing a Start Capacitor is to connect it to a motor and attempt to start it. The capacitor is probably in good shape if the motor starts up quickly and without difficulty. On the other hand, the capacitor might be broken if the motor starts up slowly or with difficulty.

What is a Run Capacitor?

A Run Capacitor is a type of capacitor that is specifically designed to keep electric motors running. Run Capacitors are made for continuous duty, but their capacitance is lower than that of Start Capacitors.

How to Identify Run Capacitor?

Run Capacitors usually have a metal or silver casing and are cylindrical. Additionally, their voltage rating in volts (V) and capacitance value in microfarads (uF) are usually labeled on them. A multimeter can be used to measure the capacitance and resistance of a Run Capacitor to test it. A Run Capacitor's capacitance ought to fall within its rated range. A Run Capacitor should have very high resistance, usually in the megohm (MΩ) range. The capacitor needs to be replaced if the resistance is low or the capacitance is less than the rated value. You can also test a Run Capacitor by disconnecting it from the motor and measuring the voltage across its terminals. If the voltage is more than a few volts, the capacitor is likely faulty.

What does a Start Capacitor do?

Provides extra starting torque: When a single-phase induction motor is starting, a Start Capacitor gives it a boost in torque. This is required because for the motor to begin rotating, it must overcome the rotor's inertia.
Creates a phase shift: The voltage and current in the motor windings are phase-shifted by the Start Capacitor. The rotor begins to rotate as a result of this phase shift, which produces a revolving magnetic field in the stator.
Disconnected after the motor reaches a certain speed: The centrifugal switch removes the Start Capacitor from the circuit when the motor reaches a specific speed. This is because, at high speeds, the motor no longer requires the additional torque provided by the capacitor.

What does a Run Capacitor do?

Provides a steady supply of power to the motor: A Run Capacitor keeps the motor windings powered consistently, promoting a smooth and effective operation of the motor.
Improves the power factor of the motor: By lowering the motor's current draw from the power supply, a Run Capacitor can enhance the motor's power factor. As a result, the electrical system may experience less wear and tear and energy costs may decrease.
Reduces vibration and noise: A Run Capacitor can assist in lowering the motor's noise and vibration. This is so that the motor can continue to run smoothly and at a steady speed thanks to the capacitor.
Extends the life of the motor By lowering the amount of wear and tear on the motor windings, a Run Capacitor can help increase motor life.

How do you check a Start Capacitor？

There are two ways to check a Start Capacitor:

Examine the capacitor visually. Keep an eye out for any indications of damage, like a protruding case, a cracked shell, or electrolyte leakage. Should you notice any indications of harm, the capacitor is faulty and requires replacement.
Use a multimeter to measure the capacitance of the capacitor. Set your multimeter to the capacitance setting and disconnect the capacitor from the motor to accomplish this. Next, make contact between the multimeter's probes and the capacitor's terminals. The capacitance of the capacitor should be displayed by the meter in microfarads (μF). The capacitor needs to be replaced if its capacitance is less than 80% of its rated capacitance.

Here are the steps on how to check a Start Capacitor using a multimeter:

Disconnect the Start Capacitor from the motor windings and turn off the motor's electricity.
Select the capacitance setting on the multimeter.
Make contact between the multimeter's probes and the capacitor's terminals.
The capacitance of the capacitor should be displayed by the meter in microfarads (μF).
The measured capacitance and the capacitor's rated capacitance should be compared. Usually, the capacitor case is printed with the rated capacitance.
The capacitor needs to be replaced if the measured capacitance is less than 80% of the rated capacitance.

How to check a Run Capacitor?

There are two ways to check a Run Capacitor:

Examine the capacitor visually. Keep an eye out for any indications of damage, like a protruding case, a cracked shell, or electrolyte leakage. Should you notice any indications of harm, the capacitor is faulty and requires replacement.
Determine the capacitor's capacitance using a multimeter. Set your multimeter to the capacitance setting and disconnect the capacitor from the motor to accomplish this. Next, make contact between the multimeter's probes and the capacitor's terminals. The capacitance of the capacitor should be displayed by the meter in microfarads (μF). The capacitor needs to be replaced if its capacitance is less than 80% of its rated capacitance.

Steps on how to check a Run Capacitor using a multimeter:

Disconnect the Run Capacitor from the motor windings and turn off the motor's electricity.
Select the capacitance setting on the multimeter.
Make contact between the multimeter's probes and the capacitor's terminals.
The capacitance of the capacitor should be displayed by the meter in microfarads (μF).
The measured capacitance and the capacitor's rated capacitance should be compared. Usually, the capacitor case is printed with the rated capacitance.
The capacitor needs to be replaced if the measured capacitance is less than 80% of the rated capacitance.

Video related to Run Capacitor vs Start Capacitor

How Does Start Capacitor Work?

The Start Capacitor is attached to the motor windings and turns on the motor.
A charge is retained in the Start Capacitor.
As a result of the Start Capacitor, the current flowing through the motor windings is not aligned with the applied voltage.
An oscillating magnetic field is produced in the stator by this phase shift.
When the rotor experiences a current induction from the rotating magnetic field, it begins to rotate.
After the motor reaches a specific speed, the Start Capacitor is disconnected from the circuit by the centrifugal switch.
When the Start Capacitor is removed, the motor continues to run on its own.

How Does a Run Capacitor Work?

The Run Capacitor begins to store electricity when the motor is turned on.
The stored energy is released back into the motor windings by the Run Capacitor while the motor operates.
This contributes to the motor's continued smooth and effective operation.
The Run Capacitor also contributes to raising the motor's power factor. The power factor indicates how effectively a motor uses the electricity it uses. An increased power factor indicates that the motor is making better use of the electrical power.
Additionally, the Run Capacitor lessens the motor's noise and vibration. This is a result of the capacitor's assistance in maintaining the motor's smooth operation and steady speed.
Finally, the Run Capacitor can help extend the life of the motor by reducing the amount of wear and tear on the motor windings.

Differences Between Start Capacitor and Run Capacitor

Characteristic	Start Capacitor	Run Capacitor
Construction	Typically has a black or blue plastic casing	Typically has a silver or metal casing
Design	Designed for intermittent use	Designed for continuous duty
Capacitance	Higher capacitance	Lower capacitance
Voltage rating	Same as the motor voltage rating	Same as the motor voltage rating
Role in motor starting and running	Provides a burst of energy to the motor to help it start	Keeps the motor running once it has started
Compatibility and interchangeability	Not interchangeable with Run Capacitors	Not interchangeable with Start Capacitors

Conclusion

In conclusion, Start Capacitors and Run Capacitors are essential components in many electric motor applications. For correct installation and maintenance, it is essential to comprehend their variations, applications, and testing procedures. Furthermore, it's critical to understand the repercussions of a malfunctioning Run Capacitor and to act quickly to replace it if needed.

FAQs about Start Capacitors and Run Capacitors

Can a Run Capacitor be Used as a Start Capacitor? No, it is not possible to use a Run Capacitor as a Start Capacitor. Run Capacitors aren't made to supply the powerful energy spike needed to start a motor. A Run Capacitor's lifespan may be shortened and damage may result from using it as a Start Capacitor. What Happens When a Run Capacitor Goes Bad? The issues mentioned above are just a few of the issues that can arise with an electric motor when a Run Capacitor fails. The motor may overheat due to a malfunctioning Run Capacitor, which could result in a fire. What Type of Motor Uses a Start Capacitor Only? A Start Capacitor is the only component used by some motor types, such as split-phase motors. Refrigerators and air conditioners are two examples of small appliances that typically use split-phase motors.