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Solenoid Problems and Solutions

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Herein, we have covered several Solenoid related topics such as Electromagnets, Solenoid & its Characteristics, Solenoid Applications and their Troubleshooting in detail.

Electromagnets

  1. Define the electromagnet and explain the left-hand rule.
  • An electromagnet is a magnet whose magnetic energy is produced by the flow of electric current.
  • The left-hand rule states that if the fingers of the left hand are wrapped in the direction of the current flow in a coil, the left thumb points to the magnetic north pole of the coil.
  1. State the main characteristics of electromagnets.
  • When electricity flows through a conductor, a magnetic field is created around that conductor.
  • The field is stronger close to the wire and weaker further away.
  • The strength of the magnetic field and the current are directly related. The more current, the stronger the magnetic field, the less current, the weaker the magnetic field.
  • The direction of the magnetic field is determined by the direction of the current flowing through the conductor.
  • The more permeable the core, the greater the concentration of magnetic lines of force.

Solenoids

  1. Define the solenoid and state the function of each part used to produce linear motion in a
  • A solenoid is an electric output device that converts electrical energy into a linear mechanical force.
  • The magnetic attraction of a solenoid may be used to transmit force. Solenoids may be combined with an armature, which transmits the force created by the solenoid into useful work. An armature is the movable part of a solenoid.
  1. Understand why solenoids are available in different operating configurations to meet different application requirements.
  • Solenoids are configured in various ways for different applications and operating characteristics. The five solenoid configurations are clapper, bell-crank, horizontal-action, vertical-action, and plunger.
  • A clapper solenoid has the armature hinged on a pivot point.
  • A bell-crank solenoid uses a lever attached to the armature to transform the vertical action of the armature into a horizontal motion.
  • A horizontal-action solenoid is a direct-action device. The movement of the armature moves the resultant force in a straight line.
  • A vertical-action solenoid also uses a mechanical assembly but transmits the vertical action of the armature in a straight-line motion as the armature is picked up.
  • A plunger solenoid contains only a movable iron cylinder or rod. A movable iron rod placed within the electrical coil tends to equalize or align itself within the coil when current passes through the coil.
  1. Describe the construction of a solenoid.
  • Solenoids are constructed of many turns of wire wrapped around a magnetic laminate assembly. Passing the electric current through the coil causes the armature to be pulled toward the coil.
  • In AC solenoids, the magnetic assembly and armature consist of a number of thin pieces of metal laminated together. The thin pieces of metal reduce the eddy current produced in the metal. Eddy current is confined to each lamination, thus reducing the intensity of the magnetic effect and subsequent heat buildup. For DC solenoids, a solid core is acceptable because the current is in one direction and continuous.
  • To prevent chattering, solenoids are designed so that the armature is attracted to its sealed-in position so that it completes the magnetic circuit as completely as possible. To ensure this, both the faces on the magnetic laminate assembly and those on the armature are machined to a very close tolerance.
  • A shading coil sets up an auxiliary magnetic field that helps hold in the armature as the main coil magnetic field drops to zero in an AC circuit. Without the shading coil, excessive noise, wear, and heat builds up on the armature faces, reducing the armature life expectancy.

Solenoid Characteristics

  1. State common problems, such as inrush current, that solenoids produce in the electrical
  • Magnetic coils are normally constructed of many turns of insulated copper wire wound on a spool. The mechanical life of most coils is extended by encapsulating the coil in an epoxy resin or glass-reinforced alkyd material. In addition to increasing mechanical strength, these materials greatly increase the moisture resistance of the magnetic coil. Because magnetic coils are encapsulated and cannot be repaired, they must be replaced when they fail.
  • Solenoid coils draw more current when first energized than the amount that is required to keep them running. In a solenoid coil, the inrush current is approximately 6 to 10 times the sealed current.
  • The voltage applied to a solenoid should be ±10% of the rated solenoid value. A solenoid overheats when the voltage is excessive. The heat destroys the insulation on the coil wire and burns out the solenoid. The solenoid armature may have difficulty moving the load connected to it when the voltage is too low.
  • Voltage variations are one of the most common causes of solenoid failure. Precautions must be taken to select the proper coil for a solenoid. Excessive or low voltage must not be applied to a solenoid coil.
  1. Describe the solenoid selection methods.
  • Solenoid selection methods include push or pull, length of stroke, required force, duty cycle, mounting, and voltage rating.
  • A solenoid may push or pull, depending on the application.
  • The length of the stroke is calculated after determining whether the solenoid must push or pull.
  • Manufacturer specification sheets are used to determine the correct solenoid based on the required force. A solenoid is selected from the manufacturer specification sheets based on required solenoid function.
  • Solenoid characteristic tables are also used to check the duty cycle requirements of the application against the duty cycle information given for the solenoid.
  • Manufacturers provide letter or number codes to indicate the solenoid mount.
  • Manufacturers provide letter or number codes to indicate the voltages that are available for a given solenoid. For example, a 2 A solenoid may be used for an application that requires a 115 V coil.

Solenoid Applications

  1. State the number of positions, number of ways, and type of actuator a directional control valve has.
  • A position is the number of locations within the valve in which the spool can be placed to direct fluid through the valve. A directional control valve normally has two or three positions.
  • A way is a flow path through a valve. Most directional control valves are either two-way or three-way valves.
  • A manual directional control valve uses a handle to change the valve spool position. An electrical control valve uses an actuator to change the position of a valve spool. In an electrical control valve, the solenoid acts as the actuator.
  1. List the different types of systems and applications solenoids may be used for.
  • A number of different solenoids may be used in a typical refrigeration system. The liquid line solenoid valves could be operated by two-wire or three-wire thermostats. The hot gas solenoid valve remains closed until the defrost cycle and then feeds the evaporator with hot gas for the defrost operation.
  • Solenoids may also be used in an oil-fired single-burner system. The solenoids are crucial in the startup and normal operating functions of the system.
  • In addition to commercial and industrial use, solenoids are used for general-purpose applications. Typical general-purpose applications include products such as printing calculators, cameras, and airplanes.
  • Industrial robots are used in all kinds of applications from welding, painting, sorting, and assembling extremely small to extremely large parts. They can replicate human movement with the added advantage of being able to lift objects of almost any size or weight repeatedly in almost any type of environment. Industrial robots use fluid power (hydraulic and/ or pneumatic) cylinders (linear motion), actuators (rotary motion), and grippers to provide the required power and movement. The cylinders, actuators, and grippers are controlled by solenoid-operated valves.

Troubleshooting Solenoids

  1. State how transients are caused and how they can be reduced within an electrical system.
  • In most industrial applications, the power supplying a solenoid comes from the same power lines that supply electric motors and other solenoids. High transient voltages are placed on the power lines as these inductive loads are turned on and off.
  • The transient voltages may be suppressed by using snubber circuits. A snubber circuit is a circuit that suppresses noise and high voltage on the power lines.
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About Ahmad Faizan

Mr. Ahmed Faizan Sheikh, M.Sc. (USA), Research Fellow (USA), a member of IEEE & CIGRE, is a Fulbright Alumnus and earned his Master’s Degree in Electrical and Power Engineering from Kansas State University, USA.