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What Is a Magnetic Solenoid?

Benjamin Arie
Benjamin Arie

A magnetic solenoid is a device that uses a coil of wire to produce a magnetic field and create linear motion. Solenoids are activated when electrical power is sent through the coil, and deactivated when the electricity is stopped. A magnetic solenoid functions in a similar way to an electric motors While the coil of a motor causes it rotate, the coil of a solenoid moves an armature either forward or backward.

The coil of wire inside of a solenoid is essentially an electromagnet. Like other types of electromagnets, a solenoid coil creates an electrical field when it is powered, which attracts ferrous metals such as iron. The armature inside of a magnetic solenoid is attracted to the magnetism produced by a solenoid. This magnetic pull causes the armature to slide through the coil.

Woman holding a book
Woman holding a book

Some magnetic solenoids use a spring to return the armature to its original position after the electromagnetic coil has been deactivated. These types of devices are often called “spring return solenoids” or “push-pull solenoids.” Other types do not have this spring, and the armature must be physically brought back into place by force or by gravity before it can be re-activated.

Both alternating current (AC) and direct current (DC) solenoids are available. AC solenoids are common in household appliances, while DC solenoids are often used in vehicles and battery-powered devices. A heavy-duty magnetic solenoid that must apply a high amount of linear force requires a larger amount of voltage than a solenoid designed for light-duty work. Long term application of excessive electricity to a solenoid can cause it to overheat and melt. The coil size of a solenoid must be matched to a specific application in order to prevent overload.

Solenoids have many different applications. One of the most common magnetic solenoids uses is on automobiles. Many cars use a starter solenoid as a simple relay to supply power when the key is turned. The motion of a starter solenoid physically closes two high-amperage electrical contacts, which allow power to flow from the car battery to the starter motor. The use of a solenoid allows the low-amperage key switch to control the starter without becoming overloaded.

Magnetic solenoids are used in many other common devices. Pinball games, for instance, use solenoids to quickly flip and bounce the ball within a machine. Some vending machines employ pushing solenoids to dispense a selected product toward the user. Robots often use magnetic solenoids attached to manipulators. This allows a robot to grasp an object or push a button on command.

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