Consider specific aspects of design. We will not promise the production of a perpetual motion machine, according to the type of creation attributed to Tesla, but the story is expected to be interesting. We will not disturb readers with clips and batteries; we suggest that you talk about how to adapt an already finished motor to your own goals. It is known that mass constructions are all used, but modern literature leaves basic fundamentals as a stern. The authors have studied the textbook of the last century, studying how to make an electric motor personally. Now we offer to plunge into the knowledge that makes up the basis of a specialist.
commutator engines often used in everyday life? This is important in the manufacture of devices: hand blenders, mixers, meat grinders. Among other things, the asynchronous motor is difficult to overclock above 3000 revolutions per minute, for a collector one, this limitation is absent. What makes the device only suitable for the implementation of the designs of centrifugal juicers, not to mention the vacuum cleaners, where the speed is often not lower.
There is no question how to make the governor of the electric motor. The problem has long been solved by cutting off part of the sinusoid cycle of the supply voltage. This is possible, because there is no difference for a collector motor, whether it is powered by alternating or direct current. In the first case, the characteristics fall, but they put up with the phenomenon because of the obvious benefits. The electric motor of the collector type works in the washing machine and in the dishwasher. Although the speeds are very different.
Easy to do and reverse. To do this, the polarity of the voltage on one winding changes( if we touch both, the direction of rotation will remain the same).Another task is how to make an engine with a similar number of components. It is unlikely that it will be possible to make a collector on its own, but it is quite realistic to rewind and pick up the stator. Note that the rotational speed depends on the number of rotor sections( similar to the amplitude of the supply voltage).And on the stator only a pair of poles.
Finally, using this design, it is possible to create a universal device. The engine works without effort from alternating and direct current. It is just that the winding is retracted, when switched on from the rectified voltage, the turns are fully engaged, and at the sinusoidal part only. This allows you to save the nominal parameters. To make a primitive collector-type electric motor does not look like a simple task, but it will be possible to completely adjust the parameters to suit our own needs.
Features of the operation of collector engines
In the collector engine is not too poles on the stator. To be more precise, only two - north and south. The magnetic field as opposed to asynchronous motors does not rotate here. Instead, the position of the poles on the rotor changes. This state of affairs is ensured by the fact that the brushes gradually move through sections of the copper drum. The special winding of the coils ensures proper distribution. The poles seem to slide around the rotor, pushing it in the right direction.
To ensure the reverse mode, it is sufficient to reverse the polarity of the power of any winding. The rotor in this case is called an anchor, and the stator is the causative agent. It is permissible to switch on these circuits parallel to each other or in series. And then the characteristics of the device will begin to change significantly. This is described by mechanical characteristics; take a look at the attached drawing to present the claim. The graphs for the two cases are conventionally shown here:
Graph of changes in the characteristics of the device
- With parallel supply of the exciter( stator) and armature( rotor) of the collector engine with direct current, its mechanical characteristic is almost horizontal. This means that when the load on the shaft changes, the nominal shaft speed is maintained. This applies to machining machines, where the change in speed does not have the best effect on quality. As a result, the part rotates when it is touched with a chisel briskly, as at the start. If the blocking moment increases too much, the movement is disrupted. The engine stops. Summary: if you want to use the engine from a vacuum cleaner to create a metalworking( turning) machine, it is proposed to connect the windings in parallel, because a different type of inclusion dominates in household appliances. And the situation is understandable. If the windings are fed in parallel with alternating current, too much inductive resistance is formed. This technique should be used with caution.
- With a sequential power supply of the rotor and stator, the collector engine has a charming property - a large torque at the start. This quality is actively used to prevent trams, trolley buses, and probably electric trains. The main thing is that with the increase of the load the turns are not broken. If you start in this mode, the collector engine at idle, the speed of rotation of the shaft will grow immensely. If the power is low - tens of watts - do not worry: the force of friction of the bearings and brushes, the increase in induction currents and the phenomenon of core reversal together inhibit the growth of a specific value. In the case of industrial units or the above-mentioned vacuum cleaner, when its engine is removed from the housing, the increase in speed is an avalanche. The centrifugal force is so great that the loads can break the anchor. Be careful when starting the collector engines with sequential excitation.
Collector motors with parallel connection of the stator and rotor windings are perfectly adjustable. Due to the introduction of a rheostat into the pathogen chain, it is possible to significantly increase the momentum. And if one is attached to an anchor branch, the rotation, on the contrary, will slow down. It is massively used in technology to achieve the desired characteristics.
The design of the collector engine and its connection with losses
When designing a collector engine, information regarding losses is taken into account. Three types are distinguished:
- Electrical is called the heat loss when current flows along conductors. To reduce this value, the windings are made of copper, having the smallest resistivity of the available materials. It is clear that it is better to take silver, and gold is just fine, but it is too expensive. Heat loss depends on the cross section. You can not choose the thickness of the conductors is too small. From this point of view, it is limited by the dissipated power, not less than that actually present in the engine. Otherwise the winding will burn. Too thick conductors of copper, however, will make the engine bulky and heavy, plus - expensive. An important addition: the engines must be accompanied by protective equipment. Thermal cut-outs or relays are appropriate, are available commercially. And the pickup values are selected below the temperature of the winding burnout( insulation).Usually 135 degrees Celsius. Technical data on the limiting temperatures of the wires are given in the data sheet.
- Magnetic losses occur in the core of the armature. It seems logical to make of steel, but this is unacceptable. It is made of insulated plates, as the core of a transformer. Otherwise, the metal rotating in the magnetic field of the stator will become like an induction cooker. Sheets are separated by a layer of varnish. Used special electrical steel with a high content of silicon. This leads to an increase in the resistivity of the material, which causes a decrease in the values of eddy currents. Finally, the steel is taken soft and specially treated to reduce the residual magnetism. If the engine is running on direct current, the housing and the stator can be made from solid pieces of metal. When work comes from a 220V or 380V network, the adjacent parts are made sheet with the separation layer by layer through varnish.
- About mechanical losses already mentioned above. They serve as a parasitic effect, in addition they save a low-power collector engine with a consistent excitation from failure. Due to the fact that the speed does not go beyond the speed limit.
Usually, when the collector motor is supplied with alternating current, a series connection of windings is used. Otherwise, there is too much inductive resistance.
To the above, we add that when the collector motor is supplied with an alternating current, the inductive resistance of the windings comes into play. Therefore, with the same operating voltage, the speed of rotation will decrease. The poles of the stator and the housing are protected from magnetic losses. The need for this is easily seen from simple experience: power a low-power collector engine from a battery. His body will remain cold. But if we now apply alternating current with the former effective value( according to tester testimony), the picture will change. Now the body of the collector engine will begin to bask.
Sketch of stator collection in cross section and on the side
Therefore, they even try to assemble the casing from electrical steel sheets, riveting or sticking with the help of BF-2 and analogues. Finally, we supplement what was said with the statement: sheets are drawn in a cross section. Often the stator is assembled according to the sketch shown in the figure. In this case, the coil is wound separately according to the pattern, then it is insulated and put back on, simplifying the assembly. As for techniques, it is easier to cut steel on a plasma machine, and not think about the price of the event.
It's easier to find( at the dump, in the garage) a ready-made form for assembly. Then wind coils of copper wire with varnish insulation under it. Obviously the diameter is chosen more. Initially, the finished coil is tensioned on the first protrusion of the core, then on the second. Press the wire so that the ends remain a small air gap. It is believed that this is not critical. To hold, at the two extreme plates, the sharp corners are cut off, the remaining gray hair is bent outward, squeezing the ends of the coil. This will help build the engine by factory standards.
Often( especially in blenders) there is an open stator core. This does not distort the shape of the magnetic field. Since the pole is the only one, one should not expect any special power. The shape of the core resembles the letter P, between the legs of the letter in a magnetic field rotor rotates. Circular cuts are made under the device in the right places. Such a stator is easy to assemble yourself from the old transformer. It's easier than making an electric motor from scratch.
The core at the winding site is insulated with a steel sleeve, and along the sides, with dielectric flanges cut from any suitable plastic.