When you cool yourself off using air conditioning, you're relying on the electrical circuit of the unit to run a motor. This converts electrical energy to mechanical and thermal energy that lets the unit cool down the air around you. Air conditioners and similar appliances rely on various elements through their circuitry, and knowing the benefits of the capacitors in these circuits can teach you more about how they work.
Advantages of Capacitor Designs
Devices and appliances like air conditioning units demonstrate the advantages of capacitor designs in their circuitry. Capacitors are made of two plates separated by a dielectric material which causes the plates to build up charge and electric potential over time. Start capacitors begin the process of a motor by providing the electrical power source. They generally use about 70 to 120 microFarads of capacitance.
The start capacitor generally has more capacitance than a run capacitor, the 7- to 9-microFarad capacitor which continues to improve the motor's performance after it has begun running. The run capacitor uses the charge of the dielectric material that separates the two plates of the capacitor to provide more current to the motor. This kind of capacitor also creates the torque, the rotational force, of the motor.
Other kinds of capacitors used in motors are based off these two basic units. Dual run capacitors involve one capacitor providing power to the motor with the other giving power to the compressor, the part of an air conditioning unit that lets the refrigerant material flow so heat can be exchanged between coils.
You can even connect a start capacitor in series and a run capacitor in parallel with a centrifugal switch for activating and deactivating its use. You can setup a capacitor start capacitor run motor with a centrifugal switch. The switch would begin in the closed position so that it can connect the power to the capacitor.
As the motor starts running, it becomes faster and faster. When it reaches about 70 to 80 percent of its normal operating speed, the switch disconnects the starting capacitor.
The run capacitor continues to work and improve the performance of the motor. These designs take advantage of the starting torque's efficiency. Make sure that if you use this design you keep the switch free from damage and debris that may hinder its switching ability. Check these capacitor setups routinely to maintain that they're functioning well.
Capacitor-start induction motors demonstrate more advantages of capacitor designs. These use a large capacitor which provides energy to begin a single-phase induction motor. The motor's torque continues until a centrifugal switch causes it to stop, similar to the other designs, but in this case, the winding uses inductors, coils of wire that induce magnetic field in response to the flow of charge as a method of powering the motor.
Other Capacitor Designs
The capacitor start, capacitor run motor used in these designs adds a run capacitor to a start capacitor. When they're arranged together, they can either have two cases for the capacitors on top of the motor or both capacitors on the side of the motor. Metal cases let the capacitors give off energy in the form of heat. When the motor begins running, the start capacitor disconnects from the circuit to save power, and the run capacitor continues.
These kinds of motors are used in single-phase applications that rely on a single power source of electricity and applications that involve hard loads. You can find them having 1/2 to 25 horsepower units to measure their power. Engineers generally ensure these motors vary in their speed by up to 10% when going from no load to a full load. You can find these motors as multi-speed motors that use two or three different speeds when collected to electrical loads. Oval or square capacitors
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- Bright Hub Engineering: Capacitor Start Motors: Diagram & Explanation of How a Capacitor is Used to Start a Single Phase Motor
- All About Circuits: Single-phase Induction Motors
- Industrial Electronics: Capacitor Start, Capacitor Run Motors
- Electric Company: Capacitor-Start/Capacitor-Run Motors
- Freedom Heating and Cooling: What’s the Difference between a Start and a Run Capacitor?
About the Author
S. Hussain Ather is a Master's student in Science Communications the University of California, Santa Cruz. After studying physics and philosophy as an undergraduate at Indiana University-Bloomington, he worked as a scientist at the National Institutes of Health for two years. He primarily performs research in and write about neuroscience and philosophy, however, his interests span ethics, policy, and other areas relevant to science.