The heat of the outdoor signage mainly comes from solar radiation and the heat generated by the work of electronic components, such as high-brightness LCM, the brightness generally requires 2000-3500nits in outdoor use so to have a good visual effect, according to the light conversion rate characteristics of the LED, about 70% of the power is converted into heat. Solar radiation (Ultraviolet) and high ambient temperature are factors that directly cause the heat dissipation difficulties of outdoor digital LCD signage. Imagine that a car parked on the side of the road without shade for 2 hours at noon in the southern summer, the air temperature inside the car can reach more than 60 °C, which shows that the heat brought by solar radiation is very terrible. SUNTUNE has repeatedly measured the air-cooled heat dissipation prototype of the whole machine, and under the environmental 50 °C solar irradiation, the brightness of the large-size vertical prototype (75 inches) is 3000nits, and the maximum temperature of the LCM surface can reach nearly 70 °C.
So what are the key points of thermal design? There are probably the following points:
1. Heat calculation, system impedance and air volume calculation;
2. App environment requirements;
3. Temperature rise requirements of each component of the product;
4. Fan selection, air duct design and overall layout scheme;
5. Scheme for thermal simulation calculation;
6. The scheme is introduced into the structural design of the whole signage;
7. Prototype high and low temperature test and fan speed regulation logic correction;
Difficulties: system impedance and air volume calculation, thermal simulation calculation accuracy.
The impedance of the system is the static pressure of the whole machine, among which the main ones with greater influence are: the smoothness of the air duct, the area of the ventilation hole, and the impedance of the dust net. Among them, the selection of dust screen should consider both dustproof ability and wind resistance cannot be too high, the higher the dustproof level, the greater the wind resistance, the higher the filter cost. A lot of dust that cannot be seen with the naked eye, but after 2 years of equipment start-up, it may be found that the filter has been covered with powdery dust.
How to determine the impedance of the whole machine? The best way is to perform simulation calculations or wind tunnel tests to obtain data, but this is the difficulty of many manufacturers in the industry at present.
Perhaps some readers think that outdoor signage as long as it is not a black screen can be fine, if dust enters the equipment, just clean it regularly. Although LG and BOE have wide temperature OC, and the temperature resistance can reach 100 °C without blackening, but OC surface temperature as long as the OC surface temperature exceeds 85 °C beyond a certain period of time will appear OC yellowing, which is caused by the polarizer and cannot withstand long-term high temperature. There is also the problem of light decay of backlight LED, as long as the temperature of the LED light board exceeds 75 °C, the curve of light decay will plummet, and it is simply impossible to withstand 50,000h. In order not to black screen, some designers directly use a lot of fans, thinking that more fans will solve the problem of heat dissipation, which is also unreasonable. If the installation position of the fan is not reasonable, the formation of turbulence will also affect the heat dissipation and play a counterproductive role. And at the same time, more fans mean more costs. The noise and power consumption are also high.
The product concept of SUNTUNE design is less fans, good heat dissipation, high reliability, but better with the dust prevention. Equipment maintenance outdoors is limited, labor is very expensive, do not think that regular maintenance works after dust into the equipment. Dust affects the life of electronic components directly. Think it more, how to maintain it if it is installed in bulk? Why not design the product well at the design stage?
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