Construction of DC Motors

The adaptation of a DC motor to an application will also depend on its construction, in the selection process. We have at disposal several different types of DC motors, each offering advantages and disadvantages based on its construction. We have three types of by-pass motors, series winding motors and compound winding motors.

Bypass motors offer minimal variation of speed across the load range and can be configured for constant power over an adjustable speed range. They are used for applications where there is a need for precise speed and torque control.

Series wound motors bring high starting torques to permanently connected loads, these torques are required to avoid damage in high speed conditions. They develop great torque and can be operated at low speeds. They are better suited for heavy industrial applications requiring larger loads moving slowly or lighter loads moving quickly.

Compound winding motors are sketched with compound winding coils for constant speed applications that require higher torque. They are often used where the primary load requires high starting torque and adjustable speed is not required. Applications include lifts, cranes and industrial shop equipment.


In electric motors, it is important to know that at a temperature of 40 ° C, the life of a continuously running ball bearing can be 3 to 4 years or more. However, for every 10 ° C of raising the working temperature its useful life decreases by an average of 50%. The correct lubrication of the bearings, in addition best generators here to allowing a better yield, avoids the rise of the temperature that damages the useful life of these equipments.

Lubrication of bearings is generally done with mineral grease. When operating temperatures are high (from 120 ° C to 150 ° C) or the rotational speeds are above 1,500 rpm, mineral oil is used for lubrication. These oils must have lubricating characteristics appropriate to the working conditions. On low power engines, initial lubrication in the assembly is provided to ensure a high number of operating hours. Sometimes the grease reserve will be sufficient for the entire life of the machine. On larger motors there is a need for external lubrication. The frequency of lubrication depends on the design of the bearings and the characteristics of the lubricants used.

Triple Speed ​​Engine

A triple-speed motor is a three-phase motor that can be basically arranged in two ways, with three separate windings or a common winding with a Dahlander. The Dahlander engine is a motor with special winding that can receive two different locks, in order to change the number of poles, thus creating two distinct speeds.

The three-phase electric motor provides unequal speeds on the same axis, but constant and mostly for only one voltage Dixon RSS35 value, because the available reconnections normally allow only the change of speeds. The power and the current for each rotation are different, being modified according to the intensity of the load, problem that can be solved through a frequency inverter.

It is of the utmost importance that the Dahlander winding be opened in the second case, otherwise, induced currents will appear when the common winding is fed, which will influence the operation of the motor. Therefore, they can not happen. The reason to avoid them is that these motors have precisely the system of a three-phase transformer. The electric motors with three windings are closed in star to avoid the same problems. If you need the triangle connection, it is mandatory to stop them when not being fed.

Speed ​​and Reversal of Direction of Rotation

The direction of rotation of an electric motor will depend on the direction of the magnetic field and the direction of current in the armature. If the direction of the field or current is reversed, the motor rotation will also be inverted. However, if both are reversed at the same time, the motor will continue to rotate in the same direction.

The speed of an engine is given by the number of revolutions of the shaft with respect to time and is expressed in units of revolutions per minute (RPM) rab motion sensor. A decrease in the magnetic field of the motor causes an increase in its speed and an increase in the field will cause a decrease in the speed of the motor. The torque developed by a motor to move a given load depends on the current intensity that the armature requests from the power supply. The higher the load, the higher the torque and consequently the higher the current. If the load is lower, the torque will be lower and the current intensity as well. To achieve a higher torque, the motor must rotate at a slower speed, so the speed of a DC motor depends on the load coupled to the shaft.


The synchronous speed is the result of 120 times the frequency in Hz, divided by the number of poles of the motor. From this formula it becomes evident that the higher the frequency that reaches the engine, the greater the speed of its work, and the reverse also results in a lower speed in an electric motor. And it is this change that the frequency inverter makes, it performs this intervention before the engine input. A rotating magnetic field lies at the basis of the operating principle of the induction machine and this field is caused as follows: a set of three independent coils, 120 ° out of phase in the space, is placed in the stator slots and circular by these three-phase lagged current coils of 120 ° in time.

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The rotating or stationary mode of the field of rotating electric machines depends in reality of the adopted reference system. For an observer located in the inductor of a synchronous machine with rotating inductor, the field of this machine is rotating. For an observer located in his rotor, the field is stationary. The simplest common ways of producing rotating fields can be summed up in the use of single-phase, rotating, DC-fed windings.

Categories of Engines

Category N motors have starting torque, starting current and normal slip (less than 5%) and can be used to drive loads where high starting torques such as pumps, fans and machine tools are not required.

Category NY Motors: They are motors with similar characteristics with normal category N engines, but are intended for starting star-triangle. In the star connection the starting torque is 25% of the value indicated for Category N engines.

Motors Category H: have high starting torque, normal slip start current. They are used where a starting torque above normal is required, such as in high inertia loads, conveyors, crushers, etc.

Motors Category HY: They are motors with similar characteristics with the motors category H, but foreseen for start star-triangle. In star connection the starting torque is 25% of the value indicated for category H electric motors.

Category D motors: have high starting torque, high starting current, high slip (greater than 5%). They are used in cases where extremely high starting torques and limited starting currents are required, such as in elevators.

Incremental encoders

Incremental encoders are motion transducers that have the competence to convert angular or linear movements into electrical information which in turn can be transformed into binary information. This information is worked and transformed into magnitudes that are understood, such as speed, position, distance, among others. The most commonly used encoders are optics, which have their operation based on a defrator that moves between a light source and a detector.

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When the light passes through the areas that are transparent to the deflector, the detector produces a visual signal, the deflector and the mask produce a closing effect so that the light only passes through them when they are aligned. There is a third point (Z), which indicates the end of a lap and the beginning of the count. When turned off, these encoders need to pass through the zero mark to restart their count. Incremental encoders offer a simpler construction. Its operation is based on the generation of pulses (A and B) coming from two equally spaced radial markings that allow position detection by pulse counting and determine the direction of rotation by the offset of points (A and B).

Rotary Machines

Rotating electric machines currently play a dominant role in the development and rise of societies, performing the most varied functions, whether in industrial or residential environments. The electric machine most applied today is the electric motor, because it presents a wide versatility reconciled to a low cost of production and a high energy efficiency.

The electric motor has as its base of operation the conversion of electrical energy into mechanical energy which manifests itself by means of a rotational movement and it also allows to convert mechanical energy into electric energy when its moving part is activated by a primary machine, to be called by electric generator. Electric motors baldor vm3538 have a wide variety, but they have in common their simple manufacturing, as they all have a static part, known as a stator, and a moving part known as a rotor. Electric machines have as their main foundation the same laws of physics and magnetism, but their different constructive forms as well as the type of electrical power supply cause them to behave in different ways.

Synchronous Electric Motors

The field winding in the synchronous machine is in the rotor, the rotating part of the motor and the winding of the armature are in the stator, stationary part. The rotor in the synchronous machines may be of the protruding or smooth type. The rotor of the synchronous machine rotates at a constant speed in steady state and this is the main characteristic for these machines. The rotating magnetic field, resulting from the interaction between the driving magneto forces due to three-phase sine-wave alternating currents, rotates at the same speed as the rotor. The rotational speed of the rotor and the rotating magnetic field is called the synchronous speed.

The field winding is fed with direct current giving the magnetic flux in the air gap. This feed is mainly achieved by two rotating collector rings, located on the rotor shaft, which make contact with fixed brushes. The excitation can be done by a direct current network or by a rectified alternating current network. Synchronous electric motors are used primarily as generating units in hydroelectric power plants, nuclear or thermoelectric power plants. Large synchronous motors are used as pumps and in fractional power applications such as electric clocks, timers and other applications. best options for vem3709t

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