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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Notes on the operation and repair of electric motors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors 1. The rotor of the stepper motor of an electronic watch is sometimes demagnetized, and even with a fresh battery, the watch hands, twitching, remain in place. You can magnetize the rotor by rubbing it with a stronger magnet, for example, from a loudspeaker. 2. The fact that it is the armature that has become unusable in the collector motor can be detected without an oscilloscope [1] and a tester. With such a breakdown, the motor sparks strongly in the brushes, does not develop sufficient power, heats up quickly (short circuit in turns) and does not always start (winding breakage). More than half of all collector motor failures happen precisely because of damage to the armature, the rest is shared by bearings and brushes. 3. Brushes for commutator motors of electric shavers, vacuum cleaners, electric drills, and other equipment can be made using an electric sharpener, a file and a hacksaw for metal from graphite scrap, battery rods, trolley bus terminal blocks, old brushes from car starters and generators. 4. Thrust bearings and angular bearings should be replaced completely, not in parts, otherwise such bearings fail faster. 5. It is noticed that the rotors of coffee grinders often burn out when shaking the device plugged into the network. Mistresses think that by doing this they speed up the grinding process. In fact, they accelerate the process of rotor wear. After all, a rapidly rotating anchor is the same flywheel that tries to keep its axis of rotation from tilting. It is worth weakening the turns of the winding, as they immediately begin to move, friction occurs, and as a result, the insulation is destroyed, and breaks or short circuits occur. It is necessary to refrain from sharp turns of the collector motors, and speed up the grinding process by placing the coffee grinder on the table at an angle of 60° (Fig. 1).
6. You can protect the engine from prolonged overload using klixons - bimetallic switches with a concave (dish-shaped) plate. The switches are made in the form of two-terminal circuits (Fig. 2), which instantly disconnect the electrical circuit when the specified temperature is exceeded. Such radio components can be removed from failed imported household appliances, imported electric motors and other equipment.
7. Many hobbyists use the engines of old washing machines for grinders and drills. If the "native" starting relay (Fig. 3) is out of order, the engine can be started with the button (Fig. 4) or the thermistor of the color kinescope demagnetization system (Fig. 5), which has the pinout shown in Fig. 6. In this case, the button or thermistor is installed on the starting winding, which has a greater resistance.
8. A three-phase electric motor with a blown (broken) winding can be used in a single-phase circuit by connecting the surviving winding (Fig. 7) or windings (Fig. 8). Moreover, the "triangle" can be used after repeated burnout. In the same way, single-phase motors with a broken starting winding wound with a thinner wire can be used. Disadvantages of this method: manual start, impossibility of use in case of short circuit in coils, power drop of three-phase motors.
9. Often, three-phase motors operating from a single-phase network burn out during experiments with the installation of working capacities. I advise you to completely abandon the working (do not confuse with starting!) Capacitors, the engine works without them. And if you still decide to experiment, then try connecting the capacitor according to the scheme in Fig. 9. Compared to traditional ones (Fig. 10), such inclusion does not lead to engine damage. To turn on according to the circuit in Fig. 9, the capacitor must have 2 times the operating voltage, and the capacitance 3 times less than in the circuits in Fig. 10. I explain the frequent failure of motors connected according to the schemes of Fig. 10 by not taking into account the resonant phenomena that are put into service in the scheme of Fig. 9 (they increase the voltage on the windings connected in series).
10. Bearings of engines operating with V-belt transmission often fail. Prevention: weakening the belt tension, rearranging the bearings in case of backlash of the bearing operating from the side of the pulley, timely lubrication. The signal about the "dry" operation of the bearing is its excessive heating during operation. It is not necessary to remove the bearing from the shaft for lubrication. It is enough to pick off the rubberized cover (Fig. 11) and fill the bearing with a suitable paste-like grease. After that, the cover is leveled and installed in place.
11. When rewinding electric motors, winding "in two wires" is sometimes used. In such cases, it becomes possible to reduce the starting currents of the motor to facilitate its start in overloaded networks. To do this, set the start-up switch. One of the options for such switching from a single triangle to a double one is shown in Fig. 12. Such schemes are used for regenerative braking by reverse current.
12. To protect three-phase electric motors from operation on two or one phase, which leads to damage to the engine, it is convenient to use the phase voltage presence indicator (Fig. 13). I made my indicator from the MTX-90 thyratrons that have served in telephone communications, connecting their extreme terminals (Fig. 14) through resistors with a resistance of 91 ... 270 kOhm (the middle terminal is not used). They are an order of magnitude more economical than the currently fashionable LEDs and shine so that it can be seen from afar, which cannot be said about semiconductor indicators.
13. You can automate the protection of a three-phase motor using relays that operate from 220 V AC, for example, RP21-003-UHL4A. The proposed circuit (Fig. 15) is more complicated than [2], but unlike it, it also works with a triangle, and turns off the unprotected motor immediately when one of the relays is triggered.
References:
Author: Y. Bearded
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