Sign & Digital Graphics

November '18

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S I G N & D I G I T A L G R A P H I C S • November 2018 • 15 pens when a problem occurs? How do you troubleshoot the issues? We'll take a look at these questions and more. Let's first start with the elements that factor into choosing an LED driver. What must a sign maker consider when starting a project? Voltage and Current Voltage and current is a good place to start. "Most LED mod- ules require either 12 VDC or 24 VDC to operate so they will need a power supply/driver to convert the incoming AC voltage to a usable DC voltage," explains Dave Hovey, an applications engineer for Scott Fetzer Electrical Group (SFEG). "The current required by all the LEDs in a sign," he contin- ues, "will dictate how many drivers will be required to illuminate the entire sign. This is normally calculated by finding out the watt rating per LED module and multiplying that by the number of modules being used in the sign." Often, signs will require more than one driver depending on the size and quantity of LEDs. In some situations, the current flow will vary with the desired brightness. Blevons says that the amount of current needed is "based on the maximum brightness the customer wants from the fix- ture or the total current demand if the LEDs are in a parallel configuration." Brightness In turn, brightness of the LEDs will impact the "the overall life they want from the LED, as the higher the current the shorter the life of the LED," Blevons says. With brightness, there are factors to consider outside of the driver—where the sign is located, how far away it is from viewers, indoor versus outdoor placement, and more. During most circumstances, "This is based on the circuit design of the product, and not determined by the power supply," Bluhm says. Temperature and Environment According to Hovey, SFEG's France LED driver has normal operating functionality between the range of -30°C and 60°C. "The weather and location of the LED driver will also help determine whether a driver rated for wet/dry/damp locations or one rated for dry/damp locations should be used," he continues. (Left) 12 volt 60 watt Class 2 Wet-Listed Power Supply from France Lighting Solutions, with over- load indicator light. (Right) 12 volt 120 watt Class 2 Wet-Listed Power Supply from France Lighting Solutions, with overload indicator light. "A wet listed LED driver can be used in any location." Externalities seem to play a role no matter the make-up of the sign. With LED signage, it can be all that more important. Whether dealing with wetness, warmth or other factors, there are elements that can impact the performance of the sign. The driver is impacted as well. "IP (ingress protection) ratings help the user determine what power supply will work in what application," offers Bluhm. "IP68 is the best one for water and dust protection, but they are typi- cally more expensive due to the process of making the unit impenetrable. If a sign maker is putting the unit inside a sign or raceway, IP54 would be sufficient and lower cost." With extreme heat or cold, there can be varying effects. "The driver will have longer life at lower temperatures but must also operate at very low possible temperatures in winter," Blevons says. "Weather certainly is a factor both from a tem- perature and moisture point of view." Blevons also mentions that other weather threats, like light- ning, should be considered; and driver surge protection is available. Size When it comes to LED drivers, size actually does matter. So, what should sign makers consider when choosing a larger or smaller power supply? There are two basic types of power supply for lighting: constant voltage, designed for a single direct cur- rent (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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