Electromechanical Education

All About Diode A diode is an electrical device allowing current to move through it in one direction with far greater ease than in the other. The most common kind of diode in modern circuit design is the semiconductor diode, although other diode technologies exist. Semiconductor diodes are symbolized in schematic diagrams such as Figure below. The term “diode” is customarily reserved for small signal devices, I ≤ 1 A. The term

Electromechanical watt-hour meters use an aluminum disk that is spun by an electric motor. To generate a constant “drag” on the disk necessary to limit its rotational speed, a strong magnet is placed in such a way that its lines of magnetic flux pass perpendicularly through the disk’s thickness: The disk itself need not be made of a ferromagnetic material in order for the magnet to create a “drag”

A three phase motor may be run from a single phase power source. (Figure below) However, it will not self-start. It may be hand started in either direction, coming up to speed in a few seconds. It will only develop 2/3 of the 3-φ power rating because one winding is not used. 3-φmotor runs from 1-φ power but does not start. Single Coil of a Single Phase Motor The single

A stepper motor is a “digital” version of the electric motor. The rotor moves in discrete steps as commanded, rather than rotating continuously like a conventional motor. When stopped but energized, a stepper (short for stepper motor) holds its load steady with a holding torque. Wide spread acceptance of the stepper motor within the last two decades was driven by the ascendancy of digital electronics. Modern solid state driver electronics

Single Phase Synchronous Motors Single phase synchronous motors are available in small sizes for applications requiring precise timing such as time keeping, (clocks) and tape players. Though battery powered quartz regulated clocks are widely available, the AC line operated variety has better long term accuracy—over a period of months. This is due to power plant operators purposely maintaining the long term accuracy of the frequency of the AC distribution

PARTS AND MATERIALS Steel flat bar, 4 pieces Miscellaneous bolts, nuts, washers 28 gauge “magnet” wire Low-voltage AC power supply “Magnet wire” is small-gauge wire insulated with a thin enamel coating. It is intended to be used to make electromagnets, because many “turns” of wire may be wrapped in a relatively small-diameter coil. Any gauge of wire will work, but 28 gauge is recommended so as to make a coil with as many

Charles Proteus Steinmetz’s first job after arriving in America was to investigate problems encountered in the design of the alternating current version of the brushed commutator motor. The situation was so bad that motors could not be designed ahead of the actual construction. The success or failure of a motor design was not known until after it was actually built at great expense and tested. He formulated the laws

PARTS AND MATERIALS 6-volt battery Low-voltage incandescent lamp (Radio Shack catalog # 272-1130 or equivalent) Long lengths of wire, 22-gauge or larger Household light switch (these are readily available at any hardware store) Household light switches are a bargain for students of basic electricity. They are readily available, very inexpensive, and almost impossible to damage with battery power. Do not get “dimmer” switches, just the simple on-off “toggle” variety used for

Calculate the voltage output by the secondary winding of a transformer if the primary voltage is 35 volts, the secondary winding has 4500 turns, and the primary winding has 355 turns. Vsecondary =

Shaded pole induction motor An easy way to provide starting torque to a single phase motor is to embed a shorted turn in each pole at 30o to 60o to the main winding. (Figure below) Typically 1/3 of the pole is enclosed by a bare copper strap. These shading coils produce a time lagging damped flux spaced 30o to 60o from the main field. This lagging flux with the undamped main

This calculator helps determine the maximum temperature a device can withstand

Perhaps the most challenging aspect of interpreting ladder diagrams, for people more familiar with electronic schematic diagrams, is how electromechanical relays are represented. Compare these two equivalent diagrams: First, the ladder diagram: Next, the schematic diagram: Based on your observations of these two diagrams, explain how electromechanical relays are represented differently between ladder and schematic diagrams.

Transformers are very versatile devices. The basic concept of energy transfer between mutual inductors is useful enough between a single primary and single secondary coil, but transformers don’t have to be made with just two sets of windings. Consider this transformer circuit: (Figure below) Transformer with multiple secondaries provides multiple output voltages. Here, three inductor coils share a common magnetic core, magnetically “coupling” or “linking” them together. The relationship

After the introduction of the DC electrical distribution system by Edison in the United States, a gradual transition to the more economical AC system commenced. Lighting worked as well on AC as on DC. Transmission of electrical energy covered longer distances at lower loss with alternating current. However, motors were a problem with alternating current. Initially, AC motors were constructed like DC motors. Numerous problems were encountered due to changing

Synchronous motors load the power line with a leading power factor. This is often useful in cancelling out the more commonly encountered lagging power factor caused by induction motors and other inductive loads. Originally, large industrial synchronous motors came into wide use because of this ability to correct the lagging power factor of induction motors. This leading power factor can be exaggerated by removing the mechanical load and over exciting

An electric current through a conductor will produce a magnetic field at right angles to the direction of electron flow. If that conductor is wrapped into a coil shape, the magnetic field produced will be oriented along the length of the coil. The greater the current, the greater the strength of the magnetic field, all other factors being equal: Inductors react against changes in current because of the energy stored

A practical application of switch and relay logic is in control systems where several process conditions have to be met before a piece of equipment is allowed to start. A good example of this is burner control for large combustion furnaces. In order for the burners in a large furnace to be started safely, the control system requests “permission” from several process switches, including high and low fuel pressure, air

The variable reluctance motor is based on the principle that an unrestrained piece of iron will move to complete a magnetic flux path with minimum reluctance, the magnetic analog of electrical resistance. (Figure below) Synchronous reluctance If the rotating field of a large synchronous motor with salient poles is de-energized, it will still develop 10 or 15% of synchronous torque. This is due to variable reluctance throughout a rotor revolution. There is

In ladder logic symbolism, an electromechanical relay coil is shown as a circle, and the contact(s) actuated by the coil as two parallel lines, almost like a capacitor symbol. Given this knowledge, interpret the following ladder logic diagram: How do we know which relay contact is actuated by which relay coil? How does this convention differ from that of standard electrical/electronic schematic diagrams, where the relay coil is