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Elevator knowledge: Some common sense that elevator maintenance personnel must master

May 23, 2018

After some basic knowledge is available, it can bring many conveniences and ideas to elevator engineering personnel.

    1. For those familiar with bridge rectification, it will be clear that adding a filter capacitor and a non-filtered DC-side output voltage value is not the same. 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 the AC side. If you measure the rectifier circuit with a filter capacitor and find that the output side voltage is lower than the AC input side voltage, it means that the filter capacitor has no effect. There is a OTIS Elevator's inverter board that detects 24 VDC. Once the monitoring point detects that 24 volts is not available, or if the voltage is lower than the rated value, it will report the damage to the computer board. If you do not check it carefully, you will think that the computer board has failed. Timely troubleshooting. It happened to me once that I encountered such a failure. I found that it was 24 VDC that was less than 24 volts and it became 20 volts. It is lower than the AC side voltage. After the capacitor is replaced, the fault disappears and the elevator runs normally.

    2. The application of half-wave rectification in a reformation has been learned that half-wave rectification can be used to achieve half-wave rectification with a diode. The half-wave rectified DC output voltage is 0.45 times that of the AC side input. An early Mitsubishi VVVF elevator showed that the floor display on each floor was achieved by lighting a light bulb and illuminating the plastic sheet marked with floor numbers. Party A should change to a digital display. According to the actual situation of the circuit, the light bulb light is AC100 volts. I connect a diode in series in the circuit, and then connect a matching resistor in series 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, and 100 volts is converted to 45 volts. A resistance is connected in series with a resistor in the digital tube circuit so that 100 volts AC from the control cabinet can be 24 VDC. The digital display circuit is powered.

    3, for example, a frequency reduction speed elevator failure to stop the elevator, you first suspect where the problem? If you have mastered the rules of elevator operation, under what state it is in the state of power generation, no load up, full load down, and deceleration running, the motors are all in the state of power generation. If there is a fault in the braking unit, it will cause the elevator to stop. . This common sense applies to all manufacturers of all models of variable frequency speed elevators.

    4. The grounding system of the lightning arrester lightning rod should be separated from the grounding system of the three-phase five-wire system, and a grounding system should not be shared. An elevator in a office building in Harbin rang after a thunderstorm in a thunderstorm and the elevator stopped operation. On-site inspections revealed that the computer board was hit by a large current and the entire room was filled with permeated odor. After checking the building’s lightning rod, Lei’s flat iron had been welded. It was on the concrete reinforcement of the building, and the concrete reinforcement of the building was welded to the grounding electrode.

    5, hidden secrets in AC and DC contactors

    First of all, their work is based on the same, the coil is energized to produce a magnetic field, so that the moving armature pulls on and off the switch.

    The difference is one of them: one passes a direct current through alternating current; the other is that the direct current contactor coil has a larger amount of wire than the alternating current contactor coil; and the third one: the core of the ac contactor has a shorting ring and the direct contactor does not. The following elaborates on the principle.

    To find out the difference between them, the key is to understand the characteristics of the alternating current and the characteristics of the coil. China's mains electricity is 50hz, which means that it changes 50 cycles in one second and 100 instantaneous currents are zero.

    The resistance of the coil is very small. In the DC power supply circuit, the winding shows a resistance characteristic. That is to say, the voltage drop is determined by the resistance of the coil. It has nothing to do with the inductance. Therefore, the number of turns of the coil should be a little more to make the resistance value larger, so as not to burn the power supply. .

    In the AC power circuit, the coil has inductive reactance, and the voltage drop is generated through the inductive reactance. At this time, the resistance value can be zero. Therefore, the number of turns can be different from that of the DC contactor, and the wire should be thicker.

    The core of the AC contactor has a short-circuit ring because the AC current flowing through the AC contactor coil has zero current. At the moment when the current is zero, there is no magnetic field in the coil, so the moving core will be released without waiting. It leaves and there is current in the coil, which is sucked again, so that the suction, release, and suction are repeated. There are one hundred repetitions in one second. This will create noise. To eliminate this noise, engineers have come up with a way to put a short circuit ring on the core that is equivalent to a closed coil. When the coil of the contactor coil is over At zero hour, an induced magnetic field is generated in the short-circuit ring. This induced magnetic field causes the magnetic field in the core to become a continuous magnetic field, thus eliminating noise. During use, if the short circuit ring breaks, noise will appear. In areas sensitive to noise, sometimes the contactor is replaced because of this reason. It is not because the contact is broken.

    According to the above reasons, the copper used in the DC contactor has a large cost, high noise and low noise. When the cost of the AC contactor is low, noise will be generated.

    6, simple judgment of electrolytic capacitor: In the process of repairing the elevator, often encounter some computer board failure, sometimes through careful observation can avoid some major losses, the surface is a computer board failure, in fact, may Is a capacitor failure, the replacement of a capacitor costs a few dollars, and sent to repair the computer board frequently hundreds of thousands. Simply observe whether the end face of the electrolytic capacitor is already bulging. If the drums are replaced in eights and nines, the problem is solved. There is also a way to dial the digital multimeter to the buzzer file and measure the positive and negative electrodes of the electrolytic capacitor with red and black pens. If there is a brief buzzing sound, the capacitor is good.

  7. The lightning protection grounding pole and the three-phase five-wire grounding pole cannot be mixed together. One day, the thunder and lightning of the thunderstorm suddenly blew up, and an office building lift stopped in Harbin and arrived at the scene to release inspections. Fault, it was discovered that the computer board was broken down in large areas. After careful inspection of the steel bars in the building and the main body of the building, the three-phase and five-wire grounding poles were soldered together, resulting in high lightning currents. The control system of the elevator was infiltrated by the lightning arrester and caused serious damage to the north of the control system.

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