What Is an AC Solenoid?
AC solenoid is the name for a solenoid that operates when alternating current is applied. A solenoid is a spirally wound copper (or other conductive) wire that conducts electricity, and is generally referred to as a coil.
While a coil is a general term for all kinds of windings, such as flat or three-dimensional ones, a coil wound in a spiral shape is called a solenoid coil, or solenoid for short.
Uses of AC Solenoid
The most common application of an AC solenoid is a solenoid valve. Solenoid valves are called solenoid valves because solenoid coils are always used in their construction.
Solenoids are mainly used in valves to stop or flow fluids such as water or oil, or to switch the direction of fluid flow,where they are also called 2-way or 3-way valves. In the home, they are used in refrigerators, air conditioners, heat pump water heaters, and other devices that utilize the fluid cooling/heating cycle.
Principle of AC Solenoids
The principle of an AC solenoid is based on the force generated by the electric current and magnetic field. This relationship between current, magnetic field, and force is also exemplified by electromagnets and the electromotive force generated by electromagnetic induction phenomena.
The principle behind Fleming’s left-hand rule states that when the middle finger, index finger, and thumb of the left hand are pointed at right angles to each other in a spiral coil, an electric current (coil) flows in the direction of the middle finger and a magnetic flux (iron core or magnet) is created in the direction of the index finger, generating a force in the direction of the thumb.
This physical phenomenon of the iron core moving by switching the current direction and turning the power on and off is used in actuators such as various solenoid valves. Fleming’s left-hand rule is actually a principle common to all electric actuators, including motors, as well as solenoids.
Types of Solenoids
As explained above, a solenoid is a coil wound in a spiral shape, and the applied electric power is converted into the driving force of a mechanical actuator in the iron core by the law of electromagnetic induction.
1. AC Solenoid
- Inrush current caused by AC tends to occur, and the noise generated is relatively large.
- Stability issues created by the strong pull force on the movable core (plunger) during inrush current.
- The solenoid itself has excellent characteristics, such as operating speed and pull force.
2. DC Solenoid
- Constant current value and stable operation.
- Unlike with AC solenoids, there is no inrush current, and the noise level is relatively low.
- The AC solenoid itself has inferior characteristics to AC solenoids due to its slow operation speed, small current and plunger pull force.
Therefore, an AC solenoid is the best choice for the characteristics. However, since there is a risk of burning out the solenoid itself under excessive load, safety operation measures such as thermal fuse and overcurrent protection circuit are required.
Solenoids are also divided into a push type (push the iron core out of the coil) and a pull type (pull the iron core into the coil) depending on the operation of the movable iron core (plunger). There is also a push-pull type that handles both types of operation.
A characteristic type of solenoid is the self-retaining type, which can fix the position of the plunger using a permanent magnet. This type of solenoid requires current flow only at the moment of plunger operation and does not require current flow during holding, making it suitable for applications where power consumption should be minimized (e.g., equipment using storage batteries).
Solenoids are available in a wide variety of specifications, and it is important to check the specifications carefully for your application before selecting a solenoid.