Analyze the reliability problems and solutions of LED guardrail tubes

1 Introduction

LED lighting is in a period of vigorous development, and the lighting projects in various cities are in full swing. Among them, the application of guardrail tubes is particularly extensive. For example, the urban lighting project in Chongqing and the lighting project in the Pearl River use a large number of LED guardrail tubes. However, since the birth of the guardrail tube, it has not left various quality problems. Most of the projects in China have experienced quality problems, and some projects have even just passed the acceptance test. In addition to the low-price bidding strategy of the government and other owners, the lack of a good pre-engineering construction and acceptance of a strict regulatory system, the practitioners do not pay attention to development, homogenization of low-cost competition and other factors that lead to the general poor quality of the guardrail tube in the market, currently Most of the domestic LED guardrail tube manufacturers have accumulated too little experience, and the investment in research and development is also an important factor. This article will introduce the reliability problems of guardrail tubes and the solutions to these problems from several aspects. I hope to provide valuable reference and reference for guardrail tube manufacturers, lighting engineering companies and owners.

2. LED guardrail tube needs to solve the reliability problem

2.1 Waterproof

The previous LED guardrail tube was sealed with silicone at the interface of the outer cover. The internal LED and circuit were bare. Due to the large temperature difference between day and night, the end of the outer cover and the outer cover were different from thermal expansion and contraction, resulting in gaps in the silicone seal. Rainwater seeps into the interior, and you can imagine what happens. To solve this problem, it is necessary to process the internal circuit and LED glue. The outer cover silicone seal is simple, but the reliability is not up to the requirements of large-scale outdoor applications.

Another problem is the problem of connectors for electrical connections. Many manufacturers often choose plastic joints for cheap, or choose poor quality metal joints. For short-term testing and use, plastics are not deformed. Waterproofing is no problem, but after sun exposure and temperature difference between day and night, seasonal climate change, plastic It will deform, which will cause the waterproof apron to fail. The rain will penetrate into the joint and cause short circuit of the wire. Especially in the charged state, the corrosion of the wire is several orders of magnitude higher than that in the uncharged state. In the experiment I have done, the signal line has been corroded like rust after being exposed to water for 8 hours. The price of poor metal joints is only a fraction of that of regular manufacturers. Due to surface treatment and material problems, it is also easily corroded by rain, resulting in signal short circuit.

2.2 UV protection

LED guardrail tubes are required to be mixed outside, and the outer cover is added on the outside. The material selection of the outer cover is another means for reducing the cost of many non-standard companies. Products with good quality will use materials with increased UV resistance, such as GE, Bayer, etc. Materials, and the quality of the LED guardrail tube is a lot of materials that use a mixture of nozzle materials, can not talk about the anti-UV, the sun is relatively large, less than a month, the cover becomes yellow, and the light effect is worse The light transmittance is also greatly reduced.

2.3 Anti-cracking

This problem is also a problem with the outer cover. If the material with the nozzle material is selected, the internal stress of the material is difficult to remove, resulting in cracking of the material. Even if a better material is chosen, if the design and production process are unreasonable, a lot of internal stress will be generated. Experienced companies will choose constant temperature protection during injection molding to minimize internal stress and have a good way to remove internal stress. If you are interested in this, you can consult experts in materials.

2.4 Line loss

Copper is a place for some manufacturers to save costs. As we all know, generally good manufacturers will use more than 1mm2 wires inside, and the wires use products that meet the national standard. If the wire area is not enough, the resistance is large, and the front guardrail tube and the rear guardrail tube have a large voltage difference. In order to make the rear LED current consistent with the front, it is necessary to increase the input voltage, thus increasing the work invisibly. Consumption, a lot of power is not driving the LED, but wasted on the wire and constant current chip. Generally speaking, if the voltage of the designed product exceeds 15%, the problem is very serious, because the current constant current chip has power consumption requirements. If the power consumption is too large, the heat will not be discharged and the chip will burn out. Everyone should now understand why many of the cascaded LED guardrails are much worse.

2.5 heat dissipation

This problem not only reflects the cost problem, but also reflects the technical strength of a manufacturer. Now some LED guardrail tube covers and low seats are completely integrated, all are plastic materials, and the LEDs are arranged very densely. At the time of heat balance, the junction temperature of the LED is already high. If the ambient temperature during operation is high, the life of the LED will be drastically reduced. The strong LED guardrail tube company will definitely have thermal designers. When designing the guardrail tube, the heat of the LED and the heat of the constant current chip should be effectively led to the atmosphere. Everyone should think that using aluminum is a better solution. Aluminum has a high thermal conductivity and can effectively transfer internal heat. In addition, the PCB should be placed close to the aluminum base as much as possible to reduce the thermal resistance generated by the potting compound. This problem involves another problem, that is, the choice of potting glue, good potting glue not only requires moderate hardness, but also requires a relatively high thermal conductivity. At present, many guardrail tube manufacturers learn from the experience of LED large screen, using Korea The potting glue, this is a good choice, I have found a comprehensive comparison of the German company's potting glue in terms of overall performance.

3. Conclusion

The electronic part of the LED guardrail tube looks simple, but to achieve high stability or to do a lot of careful design. Of course, for the current problems of the guardrail tube, the most important thing is to solve the problems of waterproof design and heat dissipation design. (Edit: Technology)

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