How to select the best electric motor in small drives

Transcription

1 How to select the best electric motor in small drives

2 Index 1. Introduction 3 2. Criteria for selecting a small electric motor Environmental conditions Protection index Installation layout Nominal power Work cycles Rotation speed Efforts necessary to get the job done 8 3. Typology AC Motors DC Motors Universal Motors Stepper Motors Servomotors Motors with brushes or brushless motors? Keys to choosing your electric motors supplier CLR: 40 years of experience working with electric motors 14 2

3 1. Introduction In the development of small industrial applications it is important to select an electric motor that responds to all the needs that your project requires. In the case of small electromechanical drives, choosing the motor is the first step before focusing on the gearbox, the gear train, or the various mechanical components. The latter will be responsible for adapting the speed and the ideal output torque; but let s not forget that the engine should be our starting point. The correct operation of the gear motor, as well as its efficiency and precision of movement depend to a great extent of the built-in motor, reason why its study and election is crucial. In this sense, we must take into account a number of essential parameters, such as protection index, installation arrangement, rated power, speed of rotation or effort. Many doubts can arise in this task, so another option is to delegate this responsibility to a company that manufactures geared motors, since it is usually accustomed to work with different engines and performs all kinds of tests and life cycle tests. In this way it is more likely to find the engine that ensures the correct operation of each drive system, or what is the same, of different types of geared motors. With the intention of helping you in this task, in CLR we have developed this ebook designed to guide you in the ever difficult purchase of electric motors. We hope it can help you. Here we go. 3

4 2. Criteria for selecting a small electric motor The choice for the most suitable electric motor for small applications is a consequence of the study of their load requirements for each application, as well as other more specific considerations such as work levels, system efficiency, application movement requirements or wear that suffers in its daily work. The main parameters that must be taken into account in the selection of an electric motor in this type of applications are the following: 2.1. Environmental conditions Under what environmental conditions can the motor of the gear motor be affected? We must pay special attention to situations of high and low temperatures. For this, the manufacturers establish limits in which the operation of the motor stops being optimum. In some cases these problems can be solved partially with the application of specific lubrications in the system. In other cases, environmental conditions such as salt fog can cause corrosion levels that end up deteriorating the engine. In order to control this problem it is important to carry out corrosion tests. The choice for the most suitable electric motor for small applications is a consequence of the study of their load requirements for each application. 4

5 2.2. Protection index The international standard IEC Degrees of Protection, applicable in most countries and especially in Europe, sets a standard for classifying motors according to the degree of protection their materials offer against the entry of foreign bodies such as dust or fibers, accidental contact and penetration of liquids. According to this standard, the technical data of the engine must include an alphanumeric code that will allow us to easily identify its level of protection. 1: Alphanumeric code which makes it possible to identify the engine protection level. The interpretation of the code of the top image would be as follows: firstly, the letters IP as an abbreviation of International Protection. Next, a digit between 0 and 6 establishes the level of protection against the entry of solid bodies, with 6 being the highest degree of protection. Finally, a digit from 0 to 9K reveals the level of protection against the entry of liquid (usually water), with 9K being the highest degree of protection. The most common certificates in an electric motor are IP21, IP22 and IP55. Thus, for example, the latter (IP55) would indicate that the motor is almost completely protected against dust and water from any angle. The Spanish version of IEC is the standard UNE 20324: 1993 / 2M: 2014 Degree of protection provided by the enclosures. It is also interesting to know the German standard DIN , which goes beyond the standard IEC and establishes more demanding conditions for electrical or electronic equipment in road vehicles subjected to adverse conditions. 5

6 2.3. Installation layout In selecting the motor of the drive mechanism we must study how the relationship between the motor shaft and the output shaft of the gear unit will be. Here we can consider different positions: Horizontal position: one whose installation position must be with its axis of rotation parallel to the mounting plane. Special application: is one that is designed and built for a specific application with one or more particular characteristics. Vertical position: one whose installation position must be with its axis of rotation perpendicular to the mounting plane or at Nominal power It is important to know what the speed of rotation and torque required by the engine will be. These two values will give us the engine power we need and which gear motor we should choose. In this sense, the nominal power is the power that the manufacturer expects from the motor, that is to say, that which can supply a motor permanently without the temperature damaging the insulation materials used and, therefore, without the machine being deteriorated. We can say that the motor is at full load when it works at its nominal power. On the other hand, if you operate for a short period of time at a power exceeding the nominal, you will be working on overload. If you work on overload continuously, you may end up overheating the machine. The nominal power is closely related to the work cycles to which the machine or the concrete application is subjected Work cycles: Continuous service: the load is constant during a long and sufficient period of operation to reach a stable temperature, for example in the ice crushing machines. Variable continuous service: the operating periods are long but the loading regime is not always the same, for example with hand tools. 6

7 Intermittent service: The working times of the motor are separated by idle times, i.e. without connection to the electrical grid. The relationship between working time and the total duration of the work cycle will give us its running factor. This service is provided in some applications such as farm ventilation systems, window opening or incubators. One-time service: the motor runs for one hour at a steady speed above the continuum, although the temperature does not stabilize and therefore does not damage insulation materials Rotation speed Knowing the rotation speed is fundamental, since together with the torque, we will obtain the power that our engine requires to carry out the small drive that we are looking for. Depending on this speed of rotation, we can classify the motors as asynchronous or synchronous. Asynchronous: are the most used. A motor is considered asynchronous when the speed of the magnetic field generated by the stator exceeds the speed of rotation of the rotor, ie the moving part of the motor and its output. In the online shop of CLR (Mootio Components) we can find asynchronous motors with a nominal voltage of 230 volts and a speed of 2,900 r.p.m. Synchronous: An engine is considered synchronous when the speed of the magnetic field of the stator is equal to the speed of rotation of the rotor. An example would be this AC motor available in the Mootio Components store with a nominal voltage of 230 volts and a speed of 500 r.p.m. Synchronous motors can be: Three-phase synchronous motors Synchronized asynchronous motors Motors with a permanent magnet rotor 7

8 2.7. Efforts necessary to get the job done Number of start-ups per operation: the number of start-ups conditions the service life of the motors, since at the time of starting the motor needs a current greater than the rated current to go from the rest state to the speed of operation. Therefore, too many starts may end up overheating the motor. Brush or brushless motors have a high starting torque and suffer less wear. In this sense, its life cycle is higher with a number of boot ups higher than the motors with brushes. Boot up types: Direct: the starting current is normal, so the motor draws a current of between three and seven times the rated current. The starting torque will be higher than the rated torque. This system is better suited for low power engines. Star-Triangle: used to limit the intensity at start-up time. In this sense, the current and the torque undergo a reduction of up to three times the nominal current. By Autotransformer: it gives the motor a voltage less than nominal, which can be between 30% and 70%. The current and the torque will vary in quadratic proportion to the input voltage. Soft electronic start: the motor receives a reduced voltage that will be increased progressively until reaching the operating voltage. At first the current and torque will be equal to the transformer start. The way in which we control the starter will condition the behavior throughout the transition period. Variable speed drive: this is the best starting method, as it allows for smoother transitions and precise speed control. By means of this it is possible to limit the starting current to values up to twice the rated current, while obtaining a suitable starting torque for any application. Turning direction reversal: Depending on our application, we will look for a motor with a type of movement and with a capacity to change direction of rotation and speed. 8

9 Type of motion of the application: Linear: The motor output consists of a longitudinal variation per unit time. It is usually measured in m / s (meters per second). Rotary: The motor output consists of an angular variation per unit time. It is usually measured in r.p.m (revolutions per minute). Manufacturer specifications: 2: Technical specifications table provided by the manufacturer. Among the specifications of the engine (engine plug), we must pay special attention to two data: the torque and the maximum current rated current. Torque indicates the force with which the motor can be maintained in one step and is measured in Newtons - centimeter (N - m or N - cm) or in grams * centimeter (g * cm). We must calculate the minimum torque needed to choose an engine that satisfies that need. For its part, the maximum current, measured in amperes (A), is the maximum current value capable of continuous movement by the motor. Maximum performance is considered when the engine is running under load at the highest performance point. In addition to these data, we must look at two other technical specifications of the engine: Current Vacuum: it is considered work in vacuum when there are no loads on the motor. Par Block: When the motor cannot perform its movement due to an excess of torque (torque) it cannot drag. This fact is interesting since it allows us to know the capacity of reaction of the engine before an overload. 9

10 3. Typology To choose the most suitable motor or geared motor for our small drive, we must consider the different types of existing electric motors, their characteristics and advantages to determine if they will provide us the torque or torque we are looking for. 3.1 AC Motors Features: are the most used. AC motors are powered by alternating current. They can be single-phase (use single-phase 230v) or three-phase (430v three-phase current). The most interesting in small drives are the single-phase, since they are suitable for small powers (below 3KW), but lack starter. Advantages: They are economical and suffer less wear and tear than DC motors. Applications: timers, sewing machines, drills or vacuum cleaners. 3: AC Motor. 3.2 DC Motors Features: DC motors DC are powered by direct current power. They can be with brushes or brushless. Advantages: generally fast response, these motors allow a greater control on the speed, as well as to change the direction of rotation and to govern the torsional pair. Applications: this type of motor is the most used in mechanisms of extractor machines and in intelligent locks. They are also used in robotics, automation and laboratory equipment. 4: DC Motor. 10

11 Universal Motors Features: used in machines that demand high speed with weak power loads, they work in both direct current (DC) and AC (alternating current). Advantages: can be manufactured for any rotation speed and have a high starting torque. Applications: those that do not require continuous use but a high torque, such as small appliances and hand tools. 3.3 Stepper Motors Features: the inductor is supplied from an external power source, so that by modifying and controlling the excitation current it is possible to vary its speed. Advantages: high position accuracy and repetition of movements, less than 5% pitch error, perfect start and stop response, reliable and durable, angle of rotation proportional to the input pulses and wide range of rotation speeds. Applications: it is ideal in solutions in which the precision of the displacements, such as hard disk heads, printers or small sanitary technology, is important. 4: Step Motor. 3.4 Servomotors Features: they are stepper motors, but with an integrated control electronics, so that it is possible to control the position and movement by degrees. Its accuracy makes it an increasingly employed engine. Advantages: Accuracy, high torque, small size, reduced maintenance cost, light load and linear speed curve. Applications: its use is more common in aeromodelling and robotics. 5: Servomotor. 11

12 4. Motors with brushes or brushless motors? Among the different types of DC electric motors, we find two widely used types: motors with brushes and motors brushless or brushless. In broad lines these are differentiated by their structure, performance and the type of control. Let s see what are the characteristics, advantages and disadvantages of both: Motors with brushes generate more friction when changing the polarity, which reduces performance and gives off heat. The brushes suffer a greater wear and, therefore, need a cleaning or to be replaced, which entails maintenance costs. As for their physical characteristics, they are larger and heavier. Among the advantages of these motors it is possible to emphasize its control by means of a simple circuit, as well as the capacity to operate in extreme conditions. In addition, they are more economical. Brushless or brushless motors do not incorporate a manifold or brushes to change the polarity in the rotor; A series of independent coils are responsible for rotating the motor and, therefore, there is no contact between the stator and the motor. This avoids any friction and sparks, so that their useful life is longer and, in addition, generate less noise. They also offer a better ratio of output power to size because they dissipate heat better. In this sense, brushless motors are smaller and lighter. In short, these engines offer greater efficiency and performance. The main disadvantages are its high price compared to the motor with brushes, and the need for an electronic control for its operation, through an expensive and complex circuit. This type of motors are used mainly in applications where the space is reduced like, for example, an electric scooter, or that require low power, like the fan of a computer. 6: Brushless Motor. 12

13 5. Keys to choosing your electric motors supplier Our suppliers must be strategic partners, a fundamental piece in the development of the project capable of offering us the best solutions and guarantees. Therefore, in the search for suppliers of electric motors we must look at a number of aspects that ensure the most suitable choice: 01 Experience in the sector The choice of the best electric motor is not always easy, since, as we have seen, it depends on a wide range of factors. A supplier with extensive experience in the sector is key, since it will have carried out all kinds of tests, besides knowing all the technical requirements and the applicable regulations to be able to advise you in choosing the solution that best suits your project. 02 Quality One factor that we should not overlook is whether the supplier meets high quality standards. These certificates are a guarantee of the quality of the services and products developed by the company, as well as its commitment to continuous improvement Integral provider When the supplier designs, manufactures and distributes it has a global vision of the product and, therefore, its involvement is total in the different phases. If the supplier addresses a project as a whole, times will be faster, and we will gain greater security and control over the development of the product, which will help us to avoid possible mistakes. Efficiency and flexibility The supplier must offer standard solutions for certain situations, but must also be able to understand the particular needs of each project and seek specific solutions to ensure the success of a particular product in the market. Specialized personnel If the supplier has an internal team of specialized engineers can offer the best advice on each project and greater proactivity, which will allow to achieve the objectives more effectively. 13

14 6. CLR: 40 years of experience working with electrical motors The Compañia Levantina de Reductores, CLR, has extensive experience in the design and manufacture of all types of small geared motors. All this, through the use of the latest technology in mechanization and injection and complying with the highest quality standards and requirements of the different sectors in which it works: automotive, vending, air conditioning, HORECA or security, among others. The CLR team is composed of highly specialized engineers who accompany the client from the initial idea to the development of the product, in order to find the solution that best suits the needs of each project in the most diligent way. On the other hand, CLR also offers standard solutions such as low voltage electric motors: you can find a wide catalog of its products through Mootio CLR online shop for mechanical components, motors and geared motors. In addition, if what you need is a displacement mechanism and is the first time you are faced with the choice of a gear motor, or simply want more information, we recommend downloading the ebook Gear motors: How to choose the best for each project. Do you need any drive solution? Download our free ebook and lear how to choose the best gear motor for each project. 14

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