Shez Posted October 28, 2016 Share Posted October 28, 2016 This is very much a "how long is a piece of string" question but any guidance would be appreciated. I've started looking at using some LED tape; the control aspect is all fine - working perfectly on the test bench with MagicQ and a DMXKing LEDMX4. What I'm now wondering is out in the field, how close does the LEDMX4 (or whatever other driver) need to be to the tape? Can the driver live in one central location with cables running a reasonable distance out to the tape? I imagine the power supply pins are fine as long as the cable is suitably chunky so it's the data signal I'm stuck on. Does it need any kind of shielding? Could you just use standard three core mains cable and not worry? The tape I'm using comprises WS2812B 5050 LEDs, 30 per meter at 5V. All pearls of wisdom welcome! Link to comment Share on other sites More sharing options...
timsabre Posted October 28, 2016 Share Posted October 28, 2016 This is very much a "how long is a piece of string" question but any guidance would be appreciated.I've started looking at using some LED tape; the control aspect is all fine - working perfectly on the test bench with MagicQ and a DMXKing LEDMX4. What I'm now wondering is out in the field, how close does the LEDMX4 (or whatever other driver) need to be to the tape? Can the driver live in one central location with cables running a reasonable distance out to the tape? I imagine the power supply pins are fine as long as the cable is suitably chunky so it's the data signal I'm stuck on. Does it need any kind of shielding? Could you just use standard three core mains cable and not worry? The tape I'm using comprises WS2812B 5050 LEDs, 30 per meter at 5V. All pearls of wisdom welcome! You can use "quite a long" cable as long as it's big enough to get the 5V there without too much voltage drop. I've done some stuff with 20m of 1.5mm mains cable. The data signal is regenerated (voltage, timing and everything) in each LED so you only need to get it intact to the first one. If it's too long for the 5V the greens and blues start to fade (red needs less voltage) - so if you put up a yellow it will go red at the far end of the tape. If it's too long for the data you start to get glitching where the pixels jump up and down the tape. Link to comment Share on other sites More sharing options...
Shez Posted October 28, 2016 Author Share Posted October 28, 2016 Excellent info - thanks Tim :) Link to comment Share on other sites More sharing options...
adam2 Posted October 28, 2016 Share Posted October 28, 2016 If a reasonable sized cable does result in excessive voltage drop, then it might be worth use of a higher voltage such as 24 volts to reduce voltage drop. At or very close to the load use a DC/DC converter to derive a regulated 5 volts from the 24 volts. The current at 24 volts will be about one quarter of that at 5 volts, and voltage drop in the 24 volt circuit of little consequence. Converters to derive a regulated 5 volts DC from an unregulated 24 volt DC supply are widely sold at low prices on fleabay and elsewhere. Link to comment Share on other sites More sharing options...
OddSocks Posted October 28, 2016 Share Posted October 28, 2016 In another guise I play with a lot of these led tapes and pixels when making and setting up christmas lights. It is quite shocking how quickly the current adds up for these leds. Each chip can take a maximum of 60mA so 1m of 30 leds could draw 1.8A makinf voltage drop one of the bigest problems in a display. White is the worst case for this and if you try a 5m tape while it is roled up and turn all the chips white, the ones near the center look decidly off white when compared to the outer ones. If you feed the supply wires from both ends this will help also if oposite ends of tape are not to close then the diference is less obvious. I would go along with Adam2 with Dc/Dc converters. I am running 12V supplies and localised droping units to 5V. Link to comment Share on other sites More sharing options...
gyro_gearloose Posted October 29, 2016 Share Posted October 29, 2016 If you're going to step the DC voltage down from 12 or 24 volts to only 5 volts then make sure you use a switch mode regulator and not a linear regulator. Linear regulators dump a lot of heat. The amount of heat can be fairly accurately calculated by simply multiplying the voltage difference between supply and output by the load. So for 24 volts feeding 1 metre of 30 LEDs via a linear regulator we would have (24-5)*1.8 = 19 * 1.8 = 34.2 Watts of heat to deal with. For 12 volts we would have (12-5)*1.8 = 7*1.8 = 12.6 Watts of heat. Link to comment Share on other sites More sharing options...
musht Posted October 31, 2016 Share Posted October 31, 2016 Christmas lights community is where a lot of the knowledge is https://www.holidaycoro.com/kb_results.asp?ID=15 https://www.dropbox.com/s/1zy9pvr8mckptws/DC%20to%20DC%20rev%203.pdf?dl=0 linked from http://www.diychristmas.org SMPSU DC>DC convertors way to go, keeps copper sizing sensible Link to comment Share on other sites More sharing options...
timsabre Posted October 31, 2016 Share Posted October 31, 2016 SMPSU DC>DC convertors way to go, keeps copper sizing sensible It depends on the distances involved, for moderate distances a length of 3 core 1mm or 1.5mm mains flex works fine and is a lot simpler. Link to comment Share on other sites More sharing options...
musht Posted October 31, 2016 Share Posted October 31, 2016 mini DC>DC convertors originally designed for use in racks and high density back planes where distributing 5/3.3V at high currents would result in silly size busbars internally. As voltage gets lower, effective distance declines fairly quickly ;-) , it`s definately worth experimenting with, over just calculating. One caution is that it`s current that heats, big ex-server 5V PSUs are effectively arc welders... Link to comment Share on other sites More sharing options...
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