Sign & Digital Graphics

November '18

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16 • November 2018 • S I G N & D I G I T A L G R A P H I C S ELECTRIC SIGNAGE "This may be one of the most impor- tant questions to ask concerning LED installations," suggests Hovey. "The size of the power supply will be determined by the number and power rating of the LEDs being used. A Class 2 power sup- ply can support up to 60 watts worth of LED modules in a sign. There are also 120-watt power supplies which consist of two, 60-watt channels. For example, if an installation required 120 LED mod- ules that are rated at .72 watts per mod- ule, the total power required would be 86.4 watts. This could be accomplished using two 60-watt class 2 power supplies (France DRV-1260-A or E) or one 120- watt power supply (DRV-12120-A or E)." Looking at how the entirety of an LED sign is constructed may also dictate the size of your driver. "Driver form factor is always a con- cern as fixtures are becoming much more ascetically pleasing as well as smaller, so drivers need to be as compact as possi- ble while still maintaining good thermal conductivity," adds Blevons. "Our drivers are compact and use high-quality potting and case materials to allow efficient ther- mal transfer to conduct heat out of the electronics to maximize life expectancy." Efficiency "High efficiency drivers," Blevons says, "generate less heat internally, requiring less heat sinking and a more flexible fixture design while still allowing a long life." Long life is an important aspect of an LED sign. Users have become accus- An overload indicator light is one feature that distinguishes SFEG's Atlas Power Series drivers (pictured) from Eco Power series. (Images courtesy of Scott Fetzer Electrical Group) tomed to expecting less maintenance and extended lifespans from their LED signage. "Most low-voltage LED power sup- plies work at 88 to 90 percent efficiency," says Bluhm. "Basically, that indicates it takes 68 watts of power to generate 60 watts if the unit is 88 percent efficient on a 12VDC unit." Latest Features Power supplies, in general, are an integral part of a sign. Says Blevons, "LED signs almost always need a switch- ing power supply (optimized for driving LEDs) to convert AC voltage to DC." But they also bring features to the sign that can enhance the functionality. One of those is the ability to dim the lighting. "Most LED suppliers provide dim- mers that are attached to the secondary output," says Bluhm. "These dimmers use pulse-width modulation to lower the light output of the LEDs." This means that signage lighting can be adjusted based on the environment or requirements of the user. "There are generally two ways (to dim). The preferred is by lowering the output current by means of a signal to the output section of the driver generated by a 0-10 V dimmer or based on a Triac or ELV wall dimmer that the driver con- verts to a signal reducing the current," says Blevons. "A second way is to rap- idly switch the power supply on and off based on a Triac or ELV dimmer causing the eye to perceive less light, but that method creates noise within the circuit. Our driver uses the first, also referred to as constant current reduction or CCR dimming." Another "feature" sign makers should be aware of is weather-proofing. With outdoor L E D signs, there are always ways for moisture to slip into the dis- play, impacting the lighting elements. Sign makers can combat this by protect- ing the driver or simply using one that is intended to resist the wetness. There are two basic types of power supply for lighting: constant voltage, designed for a single direct current (DC) output; and constant current, which offers a fixed maximum output current and a range of voltages. (Images courtesy of Credit EPtronics)

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