?The core components of the LED large screen are composed of LED lamp beads and IC drivers. Since the LED is very sensitive to static electricity, excessive static electricity will cause the breakdown of the light-emitting diodes. Therefore, grounding measures must be taken during the installation of the LED large screen to avoid death. light risk. The working voltage of the LED large screen is about 5V, and the general working current is below 20 mA. The working characteristics of the LED determine that it is very fragile in the face of static electricity and abnormal voltage or current shock. This requires us to realize this in the process of production and use, and pay enough attention to it, and take effective measures to protect the large LED screen.
The power grounding is the most commonly used protection method for LED large screens. Why is the power supply grounded? This is related to the working mode of the switching power supply. Our LED large screen switching power supply is a kind of conversion of alternating current (AC) 220V mains power into direct current (DC) 5V through a series of means such as filtering-rectification-pulse modulation-output rectification-filtering. A device with stable power output. In order to ensure the stability of the AC/DC conversion of the power supply, the power supply manufacturer, in accordance with the national 3C mandatory standard, connects an EMI filter circuit from the fire wire to the ground wire in the circuit design of the AC220V input terminal.
In order to ensure the stability of AC220V input, all power supplies will have filter leakage when they are working, and the leakage current of a single power supply is about 3.5mA. The leakage voltage is about 110V. In the case that the LED large screen is not grounded, the leakage current may not only cause damage to the chip or burn out the lamp.
If more than 20 power supplies are used, the accumulated leakage current will reach more than 70mA. It is enough to cause the leakage protector to operate and cut off the power supply. This is also the reason why our LED large screen cannot use leakage protectors.
If the leakage protection is not connected and the large LED screen is not grounded, the superimposed current of the power supply will exceed the safe current of the human body, and the voltage of 110V is enough to kill a person! After grounding, the voltage of the power shell is close to 0 to the human body. It shows that there is no potential difference between the power supply and the human body, and the leakage current is introduced into the earth. Therefore, the LED large screen must be grounded.
However, there are often customers who use the wrong grounding method to ground the LED large screen. The common ones are: 1. They think that the lower end of the column of the outdoor column structure is connected to the ground, so there is no need to ground the LED large screen; 2. Think that the power supply is the lock On the cabinet, the cabinets are connected to the structure with locks, so the grounding of the structure means that the power supply is also grounded. There are misunderstandings in these two types of methods. Our columns are connected to the foundation bolts, and the foundation bolts are embedded in the concrete. The resistance of the concrete is in the range of 100-500Ω. If the grounding resistance is too high, it will cause leakage. The current discharge is not timely or there is residual. The surface of our box is sprayed with paint, and the paint is a poor conductor of electricity, which will lead to poor contact with the ground connection of the box or an increase in grounding resistance, and electric sparks may interfere with the LED large screen body signal.
With the passage of time, the surface of the LED large screen box or structure will be oxidized and rusted, and the fixing parts such as screws will gradually loosen due to the thermal expansion and contraction caused by the temperature difference. It will lead to the weakening or even complete failure of the grounding effect of the LED large screen structure. Create a safety hazard.
Lead to the occurrence of safety accidents such as leakage current electric shock, chip interference and damage. So, what should a standard ground look like? There are 3 terminals at the power input end, which are live wire terminal, neutral wire terminal and ground terminal. The correct grounding method is to use a special yellow-green double-colored wire for grounding to connect and lock all power supply ground terminals in series, and then lead out to connect to the ground terminal.
If there is no grounding terminal on site, it can be connected to iron water pipes or iron sewer pipes and other pipes that are buried in good contact with the earth. To ensure good contact, a terminal should be welded on such a natural grounding body, and then The ground wire is tightly locked on the terminal and must not be bundled for connection. However, inflammable and explosive pipelines such as gas shall not be used. Or bury the grounding body on site.
The grounding body can be made of angle steel or steel pipe, buried horizontally or vertically in the ground as a simple grounding point, and the grounding point should be selected in a remote place to prevent pedestrians or vehicles from damaging the grounding body. When we are grounded, the grounding resistance must be less than 4 ohms to ensure the timely release of leakage current. It should be noted that when the lightning protection ground terminal discharges the lightning strike current, it takes a certain time due to the spread of the earth current, which will cause the earth potential to rise in a short period of time. If the LED large screen is connected to the lightning protection ground terminal, the ground potential It is higher than the LED large screen, and the lightning strike current will be transmitted to the LED screen body along the ground wire, causing equipment damage.
Therefore, the protective grounding of the LED large screen must not be connected to the lightning protection grounding terminal, and the protective grounding terminal must be more than 20 meters away from the lightning protection grounding terminal. Prevent backlash from ground potential. .