Some common sense that elevator maintenance personnel must m

After some basic common sense is available, it can bring a lot of conveniences and ideas to elevator engineers.

1. For those who are familiar with bridge rectification, it will be clear that the filter capacitor is not the same as the unfiltered DC side output voltage. The DC side voltage of the filter capacitor is 1.2--1.4 times that of the AC input, and the output side voltage without the filter capacitor is only 0.9 times of the AC side. If you measure the rectifier circuit with filter capacitor and find that the output side voltage is lower than the AC input side voltage, the filter capacitor has no effect. There is an OTIS elevator inverter board to detect DC 24V voltage. Once the monitoring point finds that 24V is not available, or the voltage is lower than the rated value, it will report the fault of the computer board. If you do not check it carefully, you will think that the computer board is faulty. Troubleshoot in time. It happened that I was hit by such a fault once, I found that the DC 24 volts should be less than 24 volts and become 20 volts. It is lower than the voltage on the AC side. After replacing the capacitor, the fault disappears and the elevator runs normally.

2. The application of half-wave rectification in one transformation. It is known that half-wave rectification can realize half-wave rectification with one diode. The DC output voltage after half-wave rectification is 0.45 times of the input on the AC side. An early Mitsubishi variable frequency speed control elevator, the floor display of each floor is realized by lighting the light bulb to illuminate the plastic piece marked with the floor number, and Party A should replace it with the digital tube display. According to the actual situation of the circuit, the power of the lighting bulb is AC100 volts. I serially connect a diode in the circuit, and then serially connect a matching resistor according to the resistance value in the digital tube circuit to successfully solve this problem. Connecting a diode in series is equivalent to half-wave rectification, 100 volts is changed to 45 volts, and a resistor is connected in series with the resistor in the digital tube circuit, so that the AC 100 volts from the control cabinet can be DC 24 VDC. The digital tube display circuit is powered.

3. For example, if the frequency conversion speed-regulating elevator decelerates and stops the elevator, do you first suspect that there is a problem? If you master the elevator running law, in what state is in the power generation state, no-load up, full load down, and the motor is in the power generation state during deceleration operation. At this time, if the brake unit is faulty, it will cause the elevator to stop. . This common sense applies to all types of inverters in all manufacturers.

4. The grounding system of the lightning arrester should be separated from the grounding of the three-phase five-wire grounding system. A grounding system should not be shared. After an elevator in an office building in Harbin rang in a thunderstorm, the elevator stopped running. The on-site inspection found that the computer board was smashed by the large current and filled the entire room. After checking the lightning rod of the building, a flat iron was welded. On the concrete reinforcement of the building, the concrete reinforcement of the building is welded to the grounding pole.

5. Implied secrets in AC and DC contactors

First of all, their work is based on the same foundation. The coils are energized to generate a magnetic field, so that the moving armature pulls the switch to turn on and off.
The difference is one: one through the alternating current, one direct current; the other two: the direct current contactor coil has a larger amount of wire than the alternating current contactor coil; and the third: the core of the alternating current contactor has a short circuit and the direct current contactor does not. The following is a description of the principle.
To understand the difference, the key is to understand the characteristics of the AC and the characteristics of the coil. China's mains supply is 50hz, which means that 50 cycles change in one second, and 100 instantaneous currents are zero.
The resistance of the coil is very small. In the DC power supply loop, the winding exhibits a resistance characteristic, that is, the voltage drop is determined by the resistance of the coil, and has nothing to do with the inductance. Therefore, the coil has a larger number of turns to make the resistance value larger, so as not to burn the power supply. .
In the AC power circuit, the coil has an inductive reactance characteristic, and a voltage drop is generated by the inductive reactance. At this time, the resistance value can be zero, so the number of turns can be different than that of the DC contactor, and the line is thicker.
The core of the AC contactor has a short-circuit ring because the AC current flowing through the AC contactor coil has a zero current. When the current is zero, there is no magnetic field in the coil, so the moving iron core will be released without waiting. When it leaves, there is a current in the coil, which is sucked again, so that the suction, release, and suction are repeated. There are a hundred repetitions in one second, which creates noise. To eliminate this noise, the engineer came up with a way to embed a short-circuit ring on the core that is equivalent to a closed coil. An induced magnetic field is generated in the zero-time short-circuit loop, which causes the magnetic field in the core to become a continuous magnetic field, thus eliminating noise. During use, if this short-circuit ring breaks, noise will appear. In noise-sensitive areas, sometimes the contactor is replaced for this reason, not because the contact is broken.
According to the above reasons: the large amount of copper used in the DC contactor is high in cost and low in noise, and the low cost of the AC contactor sometimes forms noise.

6. Simple judgment of electrolytic capacitor: In the process of repairing the elevator, there are often some cases where the computer board fails. In some cases, some serious losses can be avoided by careful observation. On the surface, the computer board is faulty. That is, a capacitor fails, and the cost of replacing a capacitor is a few dollars, and it is sent to repair the computer board for hundreds of thousands. Simply observe whether the end face of the electrolytic capacitor has been bulged, and if it is tamped, it will solve the problem after replacing it. There is also a way to dial the digital multimeter to the buzzer file, and use the red and black test leads to cross the positive and negative electrodes of the electrolytic capacitor. If there is a short beep, the capacitor is good.


7. The lightning-proof grounding pole of the lightning rod and the grounding pole of the three-phase five-wire system cannot be mixed together. After a day of lightning and thunder, the elevator in an office building in Harbin is stopped and transported to the scene. Fault, found that the computer board broke down in a large area, after careful inspection of the building's lightning bolt and the steel bar of the main body of the building were welded together, and the three-phase five-wire grounding pole was also welded together, resulting in a large current of lightning. The lightning-proof flat iron was poured into the control system of the elevator, causing serious damage to the north of the control system.