Device of the collector electric motor

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More often the stator of the collector engine is equipped with two poles. Whatever, vacuum cleaner, food processor, washing machine. Collector motors are adjustable, have acceptable starting characteristics, contrasting with most asynchronous ones. For ordinary citizens, there is one drawback: noisy. Therefore, an asynchronous motor is installed in refrigerators and fans. On any hoods we will meet. Consider the device of the collector engine.

Exterior view of the collector engine

Brush compartment cover

Beginners are concerned with the question - how to identify the collector engine. Easy peasy. Look at the photo of the grinder, made specifically for the VashTehnik portal: the sides of the case demonstrate the caps of insulating material for a slotted screwdriver. Having worked hard to unscrew, inside we see the contact pads, a graphite brush spring. Key sign of the collector engine. Electric tools are equipped with devices for quick replacement of graphite, which is considered a consumable material.

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Contact pad and spring of graphite brush

Brushes of the collector engine

A spare kit is included in the box. Close-up photo shows spare brushes. Each includes:

  1. Graphite Electrode. The shape varies widely depending on the type of engine. Graphite sharpened with files, files, getting the specified size. Not critical. The main thing is to avoid large gaps, the shape of the holder is specially created to reduce the backlash. The graphite electrode grinds, sparking increases up to the appearance of a circular light. The collector engine is strongly heated, smokes. The process can contemplate the persistent viewer of YouTube( see English domain).
  2. Brass contact pad is used to connect the power. In household tools more often 230 volts with one reservation: the part of the period of a sinusoid is cut off. Allows you to adjust the speed( forget the Bulgarians).Greater cut-off angle, lower shaft speed. The regulatory circuit is formed by a thyristor, adjusted by a variable resistor.
  3. The spring is stretched between the contact pad and the graphite electrode. It serves the purpose of pressure. As a result, the graphite electrode slides over the collector while simultaneously lubricating the surface. The resistance of the brushes shown in the pattern close to 7 ohms is comparable to the windings. On alternating current alignment is changing. Endowed with inductance, the resistance of the windings increases dramatically, the brushes remain the same. Graphite plays the role of limiting resistors, thanks to carbon, the rotor current is powerless to rise above 15 A.
  4. A key part of the brushes is a high flexibility cable made up of copper threads. It bends well, as the graphite brush is ground, the operation process stretches easily, reaching the desired size.

Spare brushes

The collector motor always has brushes. Some asynchronous motors have current collectors that are not divisible into sections( less often there is a collector starter, for synchronous motors).The brushing device differs in design from that shown by the collector motor. Asynchronous motor produces relatively quiet operation.

Brushes are easily split by vibrations. One of the reasons why collector engines in industry try not to use( it is difficult to find three-phase models).The second is that current collectors easily become clogged with dust, requiring regular cleaning. However, the problem is observed in asynchronous machines with a phase rotor. In the latter case, graphite does not usually smell. So, we consider today the collector single-phase electric motor.

Varistor of the collector engine

Collector engines are endowed with one unpleasant property: they spark. Causes strong interference back to the supply network, this is not the main thing. Sparking leads to unfavorable operating conditions of the engine. It is necessary to extinguish the arc varistor. The body of the elements is often rounded, with two legs. One( see photo) is attached to the contact area of ​​the brush( directly, through brass adapters), the second is soldered to the body.

Varistor of motor protection system

There are two varistors that protect the collector motor from both sides. The mechanics are as follows:

  • Increased shaft load causes severe arcing, the potential of the brush can significantly exceed the average effective value of 230 volts.
  • Varistors are punched in pairs, close the surplus to the case, the current is absorbed by the thickness of the metal, dissipated by heat losses.

We consider the scheme useless in terms of efficiency. Power is wasted. Known factor that uses sparking benefit.

Scheme for auto-tuning of revolutions of the collector engine

Thyristor scheme for adjusting the revolutions of the collector engine

The level of arcing is determined by the speed of rotation. For example, the load of the meat grinder shaft has increased. Turns temporarily drop. The sparking level changes, causing the response of a special thyristor speed control circuit. The key changes the voltage cut-off angle, compensating for the effect of the load. The thyristor circuit shown in the photo was controlled by a Philips food processor. We see a lot of protective relays that do not allow to turn on the device when the covers are open, disassembled.

The main part of the circuit is the thyristor. In the picture will find on a small metal plate radiator. The circuit through the feedback chain receives information about the strength of the sparking, and with the help of it, the speed is set. To implement these functions, the board contains a couple of variable resistors:

  1. A semicircular resistance with a cross head will serve the purpose of adjusting the operating mode of the thyristor. The value is set by the angle of rotation by the laboratory of the plant, during operation it is not subject to change by the operator.
  2. The second variable resistor. The slotted head is connected with a handle that is painted on the control panel of the housing. Sets the speed of rotation of the shaft. It is done more often in steps.

According to the purpose of the engine, it is fed in a complex way. Brown, white wiring goes to the rotor brushes, the other three set the speed mode by feeding a certain number of turns of the stator coils.

Engine collector, winding, core

The appearance of the collector

The name of the type of engines received, thanks to the presence of the collector. Look at the photo: we see a massive copper drum on the shaft, divided by sections: collector. Formed by 24 lamellas. Each end of the previous one and the beginning of the next winding. Go, crossing over. Each winding falls immediately on two adjacent in the circle lamella. As is clear from the above, the total number of coils equals the number of collector sections( 24).Located in two layers, the first lies on the surface in the niches of the core, the second hides inside.

In one half of a turn, the direction of the winding field is, say, positive, and in the second, negative. The change occurs at the time when the brush intersects the two lamellas, to which the ends of the coil fit. The correct distribution of the angles of the relative position of the brushes, the stator poles, the shift of the armature winding ensures a rational transfer of power. The coil, the perpendicular of the plane of which is as close as possible to the stator pole, has the greatest moment in this fraction of a second.

Core and windings

The core is formed by 12 sections. Each coil is wound through four holes. For example, it occupies the first, sixth niche. And so on, in a circle, four coils are formed. Therefore, when winding should follow the same procedure. It is important to correctly set the angle between( two) contact lamellae, where the ends of the wire are suitable, and the plane of the perpendicular of the coil. Approximately 45 degrees, the brushes are located towards the poles of the stator at approximately the same angle.

Coils of exactly the same length, made of a single cross-section wire, length. The collector is considered a symmetrical design. Add to this, the motor can be powered by alternating and direct current. The device of the collector electric motor is such that in coils the direction of the field changes twice per revolution. Means when powered by direct current inside the processes are not.

The core is formed by thin plates of electrical steel, pressed, separated by insulating varnish. Collector AC motors generate a magnetic field on the stator, heating the steel. Causes are eddy currents, the effect of magnetization reversal. The temperature quickly goes up. On the basis of the phenomenon are induction plates. Separation of the core plates will reduce the significance of the magnetization reversal by eddy currents. DC collector motors are much simpler, higher efficiency.

There is a second difference. When powered by direct current to create the required strength of the magnetic field of the stator enough fewer turns. Therefore, in many cases( as in ours), the winding is divided in two parts. Power is supplied by alternating current( it is necessary to get the maximum speed) - all turns are included in the work. Otherwise - a certain proportion. It becomes possible to connect the collector motors to the power source. It is important, because many asynchronous machines do not tolerate such treatment.

Stator of the collector engine

Stator of the collector engine

The order touched on the topic, told that the stator winding is divided into two parts, the core is assembled by electrical steel plates, avoiding to introduce losses of magnetization reversal, eddy currents. It remains to add: there are usually two poles - north and south. Why? Otherwise, a different design of the rotor and collector would be needed.

The stator poles are shifted by some angle relative to the brushes spatially. It is difficult to say why exactly is done. For the described construction of the collector engine, it is impossible to change the angle of the brushes relative to the poles of the stator and the correct field distribution is set by the winding method. Often unsatisfactory, then compensate.

The principle of operation of the collector electric motor achieves the best phase by using additional stator windings. Their task is to correct the form of the field. Additional windings are less than the main ones, the number is similar, located between the main poles. Compensation of reactive EMF does not require a large field strength. The turns of the additional poles are smaller, the core is often solid( reduces the cost of manufacturing the structure).The cross section of the wire often shows the appearance of the strip.

The predominant part of household appliances uses the principle of the collector electric motor. The structure of real devices often includes control devices and protection. In our case, the thermostat of the 3MP series by the Korean company Klixon. In the original version, was attached to the winding by means of an insulating tape. Often we will meet a similar sort thermoprotectors, sensors of frequency of turns. Without this, the washing machine does not work( laundry weighing mode).

Thermal Relay

We finish the review, we hope the story turned out to be interesting, we talked about the rotating magnetic field more than once, we see no reason to repeat.

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