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The suitability of a DC motor

The suitability of a DC electric motor for an application also depends on its construction, another aspect of the selection process. There are several types of DC motors.

Derivation motors feature minimum speed variation across the load range and can be configured for constant power over an adjustable speed range. They are used for applications where precise speed and torque control are required.

Series Winding Motor: exhibits high starting torques for permanently connected loads required to avoid damage at high speed conditions.

Compound Winding Motor 24138 CCK30/W33: Designed with composite winding coils for constant speed applications that require higher torque.

Permanent Magnet Motor: They have a magnet permanently embedded in their assembly (on the stator). They offer constant speed with variable load (zero slip) and excellent starting torque.

Disc-shaped armature motor: also called “pancakes” or “printed discs”, use flat rotors moved by an axially aligned magnetic field.

Coreless Motor: (and without groove) incorporate a cylindrical winding that is physically outside the permanent magnet assembly. Because laminated winding and no iron cage exist, DC motors without core have much lower inertia.


A very important factor for the use of an electric motor is its application, this is the basic requirement for a long service life, but this is not the only factor that will ensure its proper functioning.

Correct installation, maintenance and operation are extremely important and in the event of an electric motor burning, the first step is to identify the cause of the burn by analyzing the damaged winding. It is essential that the cause of the burn is eliminated to prevent further engine burns, and further damage.

Some types of winding damages and possible causes are short between turns, with failure of the wire insulation enamel, short between phases, with failure of the insulation material, short on the connection, with overheating of the connection due to poor contact.

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We can also have voltage spike, when the motor is driven by frequency inverter with incorrect parameters and the voltage unbalance, created by voltage oscillations in the phases.

The locked rotor, causing excessive trouble in starting the motor, also causes damage, generating overheating, when the power cables are very long and / or very thin.


They are thermal detectors composed of semiconductor sensors that change their resistance sharply when reaching a certain temperature. PTC – positive temperature coefficient. NTC – negative temperature coefficient.

The “PTC” type is a thermistor whose resistance rises notably to a well-defined temperature value, reported for each type. This sudden change in resistance interrupts the current in the PTC by connecting an output relay, which disarms the main circuit. Also can be applied for alarm or alarm and shutdown systems (2 per phase). For the “NTC” thermistor, the opposite of the PTC occurs, however, its use is not normal in electric motors, since the accessible electronic circuits are usually for the PTC (resistance increase).

The thermistors are small in size, do not suffer mechanical deterioration and have a faster response compared to other detectors, although they allow a constant monitoring of the process of heating the motor NUP 207 ECP/C3.

Thermistors with their respective electronic control circuitry provide complete protection against overload, overheating formed by lack of phase, over voltages or constant reversal or on-off operations. They have a low cost compared to the RTD type, however, they need a relay to control the operation of the alarm or operation.

Advantages and disadvantages of DC motor drives

Drives in DC motors are usually the ones with the greatest benefits, also in terms of reliability, user-friendly operation and dynamic control. On the other hand, this type of drive also has some drawbacks.

Advantages • Operation in 4 quadrants with relatively lower costs, continuous cycle even at low speeds, high torque at start and low speeds, wide speed variation, ease of speed control, AC / DC converters require less space, Reliability, Flexibility (various types of excitation), Relative simplicity of modern AC / DC converters.

Disadvantages • DC electric motors are larger and more expensive than induction motors for the same power, need for maintenance (due to switches), arcs and sparks due to current switching by mechanical element (can not be applied In hazardous environments), voltage between blades can not exceed 20 v, ie can not be supplied with voltage higher than 900 v, while AC motors can have thousands of volts applied to their terminals, need special measures of departure , Even on small machines.

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The main objectives of the elements in an electrical panel are: to protect the operator and to provide a command logic.

Synchronous Electric Motors

The field winding on the synchronous electric motors is located in the rotor, rotating part of the motor. The armature winding is located on the stator, a stationary part. The rotor in the synchronous motors is of the protruding or smooth type.

The rotor of the synchronous motors rotates at a steady speed in steady state. This is the main attribute for these engines. The rotating magnetic field, due to the relation between the driving magnet forces pertinent to the three-phase sine-wave alternating currents, rotates at the same speed as the rotor. The rotational speed of the rotor and rotating magnetic field is called synchronous speed.

The field winding is fed with direct current giving the magnetic flux in the air gap. This feed occurs mainly by two rotating collector rings, located on the rotor axis, which exert contact with fixed brushes. The excitation can occur by a rectified alternating current network or by a direct current network.

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Synchronous electric motors are first employed as generating elements in hydroelectric power plants, thermoelectric power plants or nuclear power plants. Large-sized synchronous motors are used as pumps and in fractional power applications such as electric clocks, timers and other applications such as pumps and in fractional-power jobs such as electric clocks.

Permanent Magnet Engine

Permanent magnet electric motors are direct current motors having a fixed magnet on the stator and a coiled rotor which is fed by direct current through a brush-switch assembly.

They offer constant speed even with variable load (zero slip) and excellent starting torque. When compared to others the permanent magnet motor has higher efficiency and lower speed adjustments.

The armature is inside a permanent magnet and DC power is supplied directly to the switch. These motors are characterized by their low power, but great application in the toy industry, the automotive industry and other industrial applications.

The advantage of this motor is the ease of speed variation, acquired only by the variation of the voltage in its terminals, and when we apply rotation to its axis, become direct current generators, which have voltage directly proportional to the speed. Because of this characteristic can be used as low cost tachometers.

These motors 237Q56LR20 have disadvantages such as low life span due to friction and sparking in the brush-switch assembly as they produce electromagnetic interference noise in electronic circuits.

Degradation of Thermal Insulation

The life of a thermal insulation can be greatly reduced when there is a significant overheating of the electric motor.

The main causes of insulation wear are line overvoltage, current intensity at start-up, dust deposit forming conductive bridges and action by acid vapors drawn by ventilation.

Some procedures may be adopted to prevent the degradation of these insulators. We can equip the power boards with protective devices and appropriate controls and always check their operation.

Periods of stopping of the motors 6302-2Z should be used to clean the winding coils, install filters on the ventilation systems of the motors, if necessary. Another important factor is to place the motors in salubrious places and to equip them with alarm devices and protection against short circuits. Also observe untimely noise and vibrations and note the temperatures during operation. Finally, check if the frequency set for the motor is actually compatible with the frequency of the mains.

When the engine exhibits a higher than desirable heating, it is sufficient to provide sufficient standstill times for the temperature to return to a suitable value.