How a Single-Phase Motor Works: The Amazing Engine in Your Home

Have you ever thought about what makes your fan spin or your washing machine turn? The answer is a small but strong engine called a single-phase AC motor. This article will explain in a simple way how this common motor works. We will look inside the motor to see its parts. You will learn the easy secret that helps this motor start and keep going. This article is good to read because you will understand the machines you use every day in a new and simple way.

What is a Single-Phase AC Motor and How Does It Run?

A single-phase AC motor is a kind of electric motor. It uses the type of power called single-phase alternating current, or AC. This is the same kind of power that comes from the wall outlets in your house. These AC motors are used in many places. They are inside your refrigerator, your air conditioner, and many of your small tools. The main purpose of any motor is to change electrical power into movement. This single-phase motor does that job very well for smaller tasks.

The basic idea behind this motor is easy to understand. The motor has two big parts. The first part is the ステーター. The stator is the part of the motor that stays still and does not move. It has a wire wrapped in a circle, which is called a winding. When AC current goes through this winding, it makes a magnetic field. The second part is the ローター. The rotor is the part of the motor that spins. In a popular type of AC motor, the induction motor, the rotor often looks like a “squirrel cage.” This rotor also gets a magnetic field from the electric current. The two magnetic fields then push and pull on each other. This action makes the rotor rotate, or spin. This spinning is what gives power to your devices. This motor operation is very important for many machines.

Why Can’t a Simple Single-Phase Motor Start by Itself?

A very simple single-phase motor has a major problem. It is not able to start spinning on its own. If you plug it in, it will just make a humming sound and stay still. This happens because the AC power makes a magnetic field that just pushes and pulls back and forth in one spot. You can think of it like pushing a swing. If you stand right in front of the swing and just push it forward and then pull it back, the swing will not really go anywhere. The magnetic field in this basic motor does the same thing to the rotor. It pushes and pulls, but it does not make the rotor begin to spin.

To make the rotor spin, the motor needs a magnetic field that spins around, not one that just pushes back and forth. A three-phase motor can make a spinning field with no trouble, but a single-phase motor cannot. The field that is made by the single stator winding in this motor just gets stronger and then weaker. It does not move around the motor. Because the magnetic field does not spin, it cannot give the rotor the first push it needs to start turning. For this reason, this kind of motor needs some help to get started. All the different kinds of single-phase motors are just clever ways to give the motor that first push.

How Does a Split-Phase Motor Fix the Starting Problem?

A split-phase motor is a smart kind of single-phase induction motor. It solves the starting problem with an easy trick. This motor has two windings on its stator, not just one. The first is the main winding. The second is an extra winding that is called the 補助巻線 or the starting winding. This auxiliary winding is the secret to helping the motor start. It is made to be different from the main winding. The auxiliary winding uses a smaller wire that has fewer loops. This makes its resistance higher.

When you switch the motor on, current goes through both of the windings. Because the auxiliary winding is different, the current that goes through it is not in sync with the current in the main winding. This difference makes a magnetic field that spins, but it is not very strong. It is not a perfect spinning field, but it is strong enough to get the rotor to start spinning. It is like giving that swing a push from the side instead of from the front. This first push is all the motor needs.

After the motor gets up to about 75% of its top speed, a special switch called a 遠心スイッチ opens. This switch is on the rotor. As the rotor spins faster, little weights fly out and open the switch. This shuts off the power to the auxiliary winding. At this point, the motor runs using only the main winding. The motor does not need the auxiliary winding anymore because the spinning of the rotor helps keep it going. This split-phase motor design is a cheap way to make a motor that can start by itself.

What are the Main Kinds of Single-Phase Motors?

There are a few kinds of single-phase motors. Each motor type has a different method for starting and a different setup. The right motor for a certain job depends on what you need that motor to do. Some motors give a strong push at the start, while others are better for running without much noise and without wasting power. Knowing about these different kinds helps you pick the right motor for a task.

Here are the main kinds of single-phase motors we will talk about:

• Split-Phase Motor: Uses an auxiliary winding to make a starting push. It is a simple and low-cost motor.
• Capacitor Motor: This motor also uses an auxiliary winding, but it adds a capacitor to it. The capacitor helps the motor get a much better starting push. There are three kinds of capacitor motor.
• Shaded-Pole Motor: This is the most simple and cheapest motor. It uses a different idea to make a weak spinning field. This motor is used for very small jobs.

The biggest difference between these motors is the way they make the second phase of current. This second phase is needed to make a rotating magnetic field. The split-phase motor does this by using a different kind of wire for the auxiliary winding. The capacitor motor uses a capacitor to make the current get more out of sync. The shaded-pole motor uses a special copper ring on its poles.

How Does a Capacitor Start Motor Work Better?

A capacitor-start motor is a big step up from a simple split-phase motor. This motor is a type of capacitor motor. Just like the split-phase motor, it has a main winding and an auxiliary winding with a centrifugal switch. The big difference is that a コンデンサ is connected in a line with the auxiliary winding. A capacitor is an electrical part that is able to store and then release energy. In this motor, the capacitor makes the current going to the auxiliary winding get much more out of sync. This makes the motor act more like a two-phase motor when it is starting up.

This larger difference in the currents makes a much stronger rotating magnetic field. The result of this is a much higher starting torque. Starting torque is the amount of twisting force a motor can make right when it starts. A motor with high starting torque can start up even if it is connected to a heavy load. This makes the capacitor-start motor great for machines that are difficult to get moving, like an air compressor or a big pump.

Once the motor gets to about 75% of its top speed, the centrifugal switch opens up. It turns off both the auxiliary winding and the capacitor. The motor then runs using only the main winding. This motor runs in a way that saves a lot of energy once it is going. The capacitor is only used for a short time at the start, so it can be a small part that does not cost much. The biggest plus of this motor is its great starting power.

What is Special About a Permanent-Split Capacitor Motor?

A permanent-split capacitor (PSC) motor is another kind of capacitor motor. Its name tells you exactly what is special about it. The capacitor is always connected in the circuit. This motor does not have a centrifugal switch to turn off the auxiliary winding or the capacitor. Both the main winding and the auxiliary winding with its capacitor are working all the time the motor is on.

Because the capacitor is always being used, a different type of capacitor has to be picked. It needs to be made to run all the time, not just for a moment. This kind of motor does not have the strong starting push of a capacitor-start motor. Its starting push is actually quite weak. But, this motor has other good points. It is very quiet and runs very smoothly. It also wastes less power than a split-phase motor.

You can often see a permanent-split capacitor motor in fans and blowers, like the ones in your home’s heating and air system. For these jobs, a strong starting push is not needed. A motor that is quiet and saves power is more important. The speed of this motor is also easy to change by adjusting the voltage. This makes it a good pick for fans that need different speed levels. This motor gives a good mix of cost and how well it works.

Can a Capacitor-Start, Capacitor-Run Motor Be Even Better?

Yes, a motor can work even better by putting the best parts of the two capacitor motors we just talked about together. This motor is called a capacitor-start, capacitor-run motor. It is the best single-phase motor, but it is also the one that costs the most. This motor uses two capacitors to work its best at starting up and when it is running at full speed.

This motor setup has two capacitors. One is a starting capacitor with a big value. It is connected in a line with the auxiliary winding, just like in a capacitor-start motor. This gives the motor a very strong starting push to get heavy things moving. There is also a second capacitor, which is a run capacitor with a smaller value. This permanent capacitor stays connected to the auxiliary winding while the motor is running.

Here is how it works: When the motor begins to run, both capacitors are in the circuit. They work as a team to make a very strong spinning magnetic field and a very high starting torque. When the motor speeds up, a centrifugal switch turns off the starting capacitor. The motor keeps running with the main winding and the auxiliary winding, which still has the run capacitor. This setup makes the motor run very smoothly, quietly, and without wasting power. This motor gives you the best of everything: powerful starting and great running.

What is a Shaded-Pole Motor and Where is It Used?

A shaded-pole motor is the most simple and least costly kind of single-phase motor. It is built in a very simple way. This motor has poles on the stator, and a piece of each pole is wrapped with a copper ring. This ring is called a shading coil. That is how the motor got its name. The shaded-pole motor does not have an auxiliary winding or a capacitor. It is a very different kind of motor.

Here is the idea of how it runs. When AC current goes through the stator winding, the magnetic field it makes begins to change. The shading coil pushes against this change. This action causes the magnetic field in the “shaded” part of the pole to be a little bit behind the field in the main part. This delay makes a very weak rotating magnetic field. The field looks like it is moving from the unshaded part of the pole to the shaded part. This is just enough to make the rotor begin to turn.

Because the spinning field is very weak, this motor has a very weak starting push. It can only be used for small jobs that are easy to start. The shaded-pole motor also wastes a lot of power. But, it is very cheap to build, you can count on it, and it is simple. You will see this motor in small fans, pumps for fish tanks, and other small things where a low price is the most important factor and the motor’s low power is not an issue. This is a very popular small AC motor.

How Can We Compare the Different Kinds of AC Motors?

To pick the right single-phase motor, you need to look at how they are different. Different motor types are good for different things. The main things to look at are the starting push, price, how much power it saves, and how quiet the motor is. A simple table can help us see the differences in the motor designs. This comparison will show you why one motor is used for a big machine and another motor is used for a tiny fan.

Here is a table to help you compare the main kinds of single-phase motors:

As you can see, the motor you pick is a choice where you give up one thing to get another. If you need a motor with a strong starting push for a tough job, you will have to pay more for a capacitor motor. If you just need a small, inexpensive motor for a fan, a shaded-pole motor is a very good choice. Understanding this special quality of each motor is very important.

What is the Best Way to Choose a Single-Phase Motor?

The best way to choose a single-phase motor depends completely on the job you need it for. You have to think about what the motor must do. You should ask yourself some important questions. First, how much starting push does the motor need? If the motor has to start something heavy, like a piston in a compressor, you need a high starting torque. A capacitor-start motor would be a smart pick.

Second, how much can you spend on the motor? The price is often an important thing to think about. For a simple machine where working perfectly is not the most important thing, a low-cost motor like a split-phase or shaded-pole motor might be the best choice. Third, how important is saving power and being quiet? For a motor that will be on for many hours each day, like in an air conditioner, a motor that saves power like a permanent-split capacitor motor will save you money on your electric bill. A quiet motor is also much nicer for using in a home.

Last, think about the size and power needs. The horsepower of the motor needs to be the right amount for the machine it will power. You also need to be sure the voltage and current the motor needs will work with your electrical system. By thinking about each of these points—starting push, price, power-saving, and power needs—you can pick the perfect single-phase motor for any job. The right motor will do its job well and last for many years.

留意点

• A single-phase AC motor changes the electricity from your house into movement.
• A simple single-phase motor cannot start by itself because its magnetic field just pushes back and forth in one spot. It needs a spinning magnetic field to start.
• Split-phase motors use a special auxiliary winding to make a weak spinning field to get the motor started.
• Capacitor motors use a capacitor with the auxiliary winding to make a strong spinning field. This gives them a much stronger starting push.
• There are three kinds of capacitor motor: capacitor-start (strong starting push), permanent-split capacitor (quiet and saves power), and capacitor-start, capacitor-run (works the best, costs the most).
• Shaded-pole motors are the most simple and cheapest motors, but they are very weak and are only used for small jobs.
• Picking the right motor means matching the motor’s qualities (like starting push and price) to what the job needs.