Design and operation of the DC motor

Not every electric motor can be uniquely called able to work from DC. As for the collector type. It is based on a device working principle of the DC motor. The stator consists of a set of windings, each works only on a limited part of the arc of the shaft speed. Otherwise, it is impossible to realize the concept.

Work commutator motor

The commutator motor is used throughout household appliances. 90% of domestic applications accounted for this segment. Engines washing machines, vacuum cleaners, electric tool. Except call refrigerators, fans, vetroduvki, some stretching. Caused by the low noise requirements. Anyone who has heard little car goes from a battery, understands. At night, hear every rustle, commutator motor would be brought to rustle. Try to include one or two seconds grinders at six o'clock in the morning - will understand.

According to the legislation in the dark sound pressure level does not exceed 30 dB. Otherwise, the equipment will prevent restful sleep. The noise caused by the friction of the brushes on the commutator, the motor rotor is relatively heavy, the slightest misalignment given in the bearings. Backlash is, massive moving parts, the acoustic effect is noticeable. In commutator motors abound shortcomings, but can operate from DC. To reduce the size, reduce the number of coils. To uniquely specify the direction of rotation at least three poles, and never operate in parallel.

DC motor

DC motor

In the commutator motor home appliances great number of rotor poles. Below is a simplified drawing for DC. The commutator motor works in a similar mode, the stator magnets more, all electric. Power is conducted with alternating voltage of 220 volts. We approached the main secret! There is no difference, feed commutator motor AC, DC. From the standpoint of the layman. There are some features:

  1. When powered by direct current efficiency is improved. Input power proportionally reduced, achieving greater efficiency of use. The stator winding is provided with not two - three terminals. When powered by direct current uses a part of the turns. Variable flow through the stator coil.
  2. At constant field magnetization reversal effect disappears. Drastically reduces the heating of an electrical steel cores DC motor. It reflects lower requirements for the construction of the base substrate rotor and stator. You can not separate the magnetic cores on a plate with insulation varnish. Whatever it was, most of the collector of DC motors at the same time are also suitable for working with variables. Magnetic circuits composed of electrical steel plates.
  3. An indirect advantage is the greater stability of revolutions. For regulating the speed of rotation is used a DC voltage amplitude change, AC - using thyristor key clipped sinusoid portion of the supply line. The latter option is used washing machines.
  4. The reverse alternating current windings are rewiring. Change of direction turn relative to each other. Procedures for special relays operate in the washing machine. In DC motors the stator pole is replaced by iron (neodymium) magnet. Enough to change the polarity of the power supply for the reverse. The operation can be carried out using either a relay or contactor. If the windings are powered electricity, to change the direction of shaft rotation is applied switched over.

In the commutator motor of household appliances connected in series to the rotor stator. For power transmission on the shaft is used as a current collector drum divided sections. The electrodes serve as carbon brushes with clamping springs. The main body of the stator and rotor separated findings, providing possibility of implementing the reverse function. Additional contacts may be auxiliary, three Hall sensor output (two tachometer) closure thermal fuse.

As the shaft torsion brush gradually switched to the next section, the rotor pole moves. The stator is in the same place. Note the polarity changes at twice the mains frequency (50 Hz), the nature of the interaction remains the same. Same poles repel each other, dissimilar attract. By special winding distribution, switching from the reservoir is provided in the right direction of rotation. Engine is shown independent of the supply voltage type (AC or DC). Some features of the collecting equipment unique to this type of device, see below.

As the brushes movement of the drum there is a spark

Deflection effect is often used to advantage, in the form of interference disadvantages serve estimation rotational speed. When the load increases the shaft speed is reduced. Value falls back EMF undesired effect leads to a decrease in the level of arcing. A special circuit monitors a factor increasing the supply voltage. rotational speed is restored. Such circuits find a kitchen machines; washing machines special gauges (tachometer) used for rotation monitoring.

Principle of operation

Operating principle

To extinguish the sparks applied varistors

The magnitude of the emf increases to an unacceptable size, protection resistance in the tens of thousands of times is decreased, the excess current is shorted housing. Varistors are used in pairs. Combine both the brush through the commutator motor housing. Plugs vacuums often lack ground terminal, successfully supplied varistor protection. Iskra closed steel case, because of the large size, mass heating is absent. LETHAL take one hand commutator motor with such refinements, the other - grabbing grounded metal structure (fire ladders; water, sewer, gas pipes; lightning conductors tire; Braid antenna cables).

Removable cheek on the body

The housing is provided with a removable power cheeks brush change over in minutes. Safeguard against the need to disassemble the unit for maintenance. wear is very strong sign of the brush sparking. worn out equipment. New brush with ointments strong spark. In the case of wear observed drop in power. Drill stops rotating drill bit stops the drum of the washing machine at a nominal weight of the loaded laundry. It is not always possible to get the original brush, components can erode up to the required size grinding tool.

motor revs

motor revs

Arcing speed stall

Sparking breakdown rotations observed at drum contamination. The rotor is removed, cleaning is conducted by suitable means (alcohol).

The device is a DC motor is different from models operating under AC voltage. The above applies to any type of equipment.

Work dc motor

Under current collector motor simplest two sections. Degenerated collector drum. Each contact lamella (plate on the shaft) takes a half turn. One brush is supplied with a positive potential, the second - negative, it varies according to the magnetic pole pitch. Active at each time point are two (in the above structure). The stator can be formed by a constant electric field, or a metal magnet. Last used children's toy cars.

How does the DC motor. For example, in the initial time of the winding are arranged as shown in the figure. In this example, the poles are no longer two, as discussed above, - three. The minimum number for a stable run of the electric DC motor in the desired direction. The windings are connected in wye, each pair having one common point. The field strength forms a two pole negative, one positive. The permanent magnet is worth, as shown in the figure.

The simplified drawing of DC

Simplified drawing case DC

Every third turn, the field redistribution so that the poles are shifted according to the change in the supply voltage lamellae. In the second we see the diagram: winding numbers shifted, the pattern remained in space. Guarantee of stability: one pole is attracted to the permanent magnet, the second repelled. If you want to get the reverse, changing the polarity of the batteries (battery). The result is two positive pole, a negative one. The shaft will move counterclockwise.

We believe that the action of direct current electric motor principle is now clear. We add today common valve type engines. Many are thinking to make alternate field on the stator, the rotor would be of a permanent magnet. In a first approximation, the valve type engine. Direct current is supplied to the desired stator winding through the dial keys, thyristors. The result is a desired field distribution.

Benefits of the scheme to reduce the amount of friction parts that cause the need for servicing, repair. Thyristor control unit is rather complicated. Allowed to organize switching using slats. Simultaneously design will rough shaft position sensor (plus or minus the distance between the contact pads of the shaft axis). Valve engines are not new. Widely used by specific industries. Help accurately withstand speed. At home valve engines are hard to find. A certain similarity can be seen in the washing machine. Speech on the water draining pump (magnetic rotor AC only).

Specifications DC motors are better than when powered by alternating current. class of devices is widely used. DC motors are often used in the batteries of various kinds of food. When there is no choice. Advantages of power circuits allow the batteries last longer.

The windings of the stator, the rotor includes successively, in parallel. The latter is used in a loaded state in the starting shaft. There has been a dramatic increase in speed can lead to negative consequences, if the rotor is too easy. We mentioned about such subtleties in the topic of designing engines with their own hands.

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