I have a question about voltage supply for LED lighting. For the annual Glow festival in Eindhoven I’m designing a really big tensegrity construction with WS2812B LEDs inside the tubes. However, can’t decide wether to use a 220v to 5v voltage converter inside each of the tubes, or have a big voltage converter delivering power to a number of tubes. The second solution has my preference, but I don’t know if I might run into problems because I’m running 5v 7,2A over 6 - 10m long wires.
If anyone could help me with this problem would be great, I don’t really know where to look for this. It would be great if somebody has something that could point me into the right direction!
Advantages / disadvantages to both.
220vac distro will allow the failure of one tube w/o killing the whole display. Of course it’s less safe.
5v distro would be safe “er” … but if the common power supply fails … my 2 pence …
Well since your wires are so long you will have significant voltage drop over 5v. So you might want to consider an adjustable supply so you can account for the drop by powering at say 6v instead.
Keep us posted! I’ve started the working on Christmas lights for my house with the same LEDs. I’ll need to make some of the cables at least as long as yours (a couple of them probably longer). Current plan is to use 12-volt along the line and convert to 5-volt just before the strips. Once the actual lines are run through the attic, I’ll be able to test both 5v and 12v from a computer power supply I plan on using.
As well as the length of the power lines, does anyone see any problems with the length of the signal wires? If using Cat6 to carry the signal, are there any length limitations for a FastLED/WS2812B combination?
I’ve used a similar scheme as @allanGEE where I run power via 12V and then put a 12-5V step down converter at the point where the strips are being powered. I would also have some concern with the SPI over that distance, although I’ve seen some post where people talk about just using an RS485 chip on the SPI lines for extending the distance, but have never tried that approach.
IMHO … there should be no issue w/Cat 6 for any modest length as to supply …
vDrop = 2 * Current * Length * figure for wire gauge resistance in this chart http://www.daycounter.com/Calculators/AWG.phtml
Thank you all for the discussion. I like the idea @allanGEE proposed of distributing 12V and using a 12V to 5V converter in the tubes. If done correctly I think I will be able to have a constant 5V in every tube. It might also allow me to purchase a higher quality power supply.
For the communication, we want to communicate over Artnet (work with software). So we want to build teensy LC’s in every tube (total of > 150 tubes) with an ethernet receiver and use ethernet switches for the data traffic.
Sounds like a very good plan. When I upgraded the fled installation (https://hackaday.io/project/3-fled) I did something similar in terms of power. A 12v line down into the box, and then a few 5v regulators inside. This massively reduced the heat dissipation inside the box too.
Let us know how artnet goes always been intrigued by that.
How many LEDs will you have per strip? 16-17 LEDs – at full brightness and all white – will draw about 1Ah. There are inexpensive buck converters on eBay that will handle 3Ah, or 50 LEDs at full bright white…
and they’re small enough to be unobtrusive in most projects.
My current plan (which may change) for my Christmas lights, is to “build in” a 3Ah buck converter, capacitor, and resistor (for the signal line) into connectors. 12 volt supply goes in one end, 5v supply and signal come out the other.
@Ben_Delarre The problem with setting a central supply to 6v to account for voltage drop is - the drop isn’t constant if you run arbitrary patterns which take varying current. (The drop is proportional to instantaneous current) When it’s all off, the pixels will see nearly 6V, which is too high.
The idea of sending out 12v and using step-down (buck) DC-DC converters local to each tube is much better.
@allanGEE Every tube of 2m will contain 120 LEDs, 2 strips of 30 LEDs/m, so I think I’ll need 10A.
I think its safe to say that using a 1000W 12 - 30V PSU and a DC-DC converter in each tube is a relatively cheap and safe way to power the LEDs. I will propose this to the electronics expert at my university and I’ll keep you updated about his opinion! Thank you so much for your help everybody.
Short summary: they’re very good, you don’t need any external capacitors, you do need to design custom boards to mount them (they require a couple of passives and a fuse). But if I were to do it all again, I’d look for a 12V LED solution and avoid them altogether.
@Robert_Atkins those Murata DC/DC converters look awesome! And they go up to really high amps. We were to design custom boards for the sensor chips and stuff anyway, so that’s perfect actally. Thanks for the tip!
As for what you mention about 12V LED solutions, do you mean using e.g. WS2811 strips? Isn’t it possible that I’d run into voltage drop problems as mentioned before?
Voltage drop is much less of a problem with 12V strips, because they take about 1/3 the current for a given number of LEDs (thus less resistive drop) and they have also more voltage margin for drop (diff between 5v and Vfwd vs 12 volts and 3xVfwd).
(Vfwd is the LED voltage when illuminated, and is around 3 volts for blue and green LEDs)
Since each controlled channel goes through 3 LEDs in series, you get more light per mA. However, this means you only control the LEDs in groups of 3, so your visual “pixels” (controllable unit) consists of three consecutive tricolor LEDs. That’s a tradeoff which makes sense in some cases, where you don’t need the finest resolution of control.
What @Zeph_Smith says re: voltage drop being less of an issue for 12V.
As well as WS2801-based 12V “square” pixel strings, there are also single dome-led WS2812 strings that run on 12V (I think they’ve got some kind of regulator or current-limiting resistor built into each pixel? They waste a bit of power but you’re not on battery so it doesn’t matter), and there are also 25mm wide strips with 3-LED “clusters” at ~30mm pitch that run on 12V. Someone also found normal width single pixel addressable strips that had 12V-5V DC-DC converters integrated into the back of the strip every 50cm!
Check Ray Wu’s Alibaba site for those last two or poke around here for the links.
What