Powering and *protecting* 240 WS2812Bs - Page 1
Forum section: electronics / beginners

author: thegoonden
author_rank: Newbie
timestamp: March 15, 2020, 07:52:05 pm
content: Greetings, I'm told this is a place of epic wisdom, and I need some.TLDR: have perfectly working WS2812B project but would like to deploy it with a less insane PSU and decent protection.I'm much worse than an outright beginner, I have decade of messing around with electronic music gear and small PAs....but outside the case generally.I have weird notions.These weird notions have led me astray.I built a clock and psychedelic light using concentric WS2812B rings.The test bed used 104, runs on an 5v 8A laptop style power brick and has functioned perfectly well despite being a veritable nightmare of lashed up connections.The final unit will be properly housed and will use 241 LEDS.So being the audio idiot I am, I bought a 5v 30A supply......lots of headroom, easy life for the unit etc, sure it's only 150W.My brother, younger, but wiser, and a qualified electrician, then reminded me that 500v or 5v, 30A can cause a very VERY bad day.And since this unit is a present for my 22 year old crazy hippy chick padawan/adopted niece, I'd quite like it to not burn her house down.I'd like to limit the whole shebang to a more reasonable current.Ideally a 10A laptop style brick.Based on testing with the 104 LED array and the 241 array on an 8A supply (software limited and showing only rainbows, no whites), with the help of a multimeter with a useless 10A range, it works out to about 45ma/LED in 255 255 255 RGB and 255 brightness. The datasheet says to allow more, naturally......but these are knockoffs and not as bright.I can use the FastLED software current limiter.......but it's hardly safety critical reliable.Is there anything I can put between the PSU and the circuit (that works and I really don't wanna mess with), that will gently limit the current should the software limiter fail. I intend to also add a polyfuse (rather 2 paralleled) to the 5V circuit to hopefully protect the PSU from a short or other fault condition.Also the array is wired in a star configuration with the individual leads to each ring being only good for around 2A, so, they acted as an admittedly half arsed extra short protection, because should a ring suffer an internal short, the wire will melt/ping off its pad, probably even before the board track explodes.OR.....a 15A bare supply (I already designed the enclosure to include the 30A monster, so this is no worries.)But I'd really like such a supply to be protected VERY well.Given the choice, I'd like to go with the lower current supply, and use something like an audio "soft knee limiter"........essentially the same thing a PSU does when overtaxed, but by intention rather than because the circuit is in its death throes like a PSU is.But I've no idea what the in-circuit equivalent of that is.Complication: it's a PCB free design, so any solution needs to be mountable "in line" between the input to the light's power rails ( the arduino nano and its ancillary gear, a preamped mic, an RTC, some pots and buttons, run from this too) and the PSU.This has all been tested as I said using carefully chosen displays, the software limiter and my left hand being 3cm from the barrel jack, on the 8A.I should really learn more about how to do something like this instead of begging for a solution, but her B'day is in 3 weeks, and until my brother put the fear of god into me, I was about to build it up tonight with the 30A unit.Really appreciate any advice.PS: One other minor wrinkle.The 30A supply has yet to be powered up. But when testing to see if the 2 5v outputs on it were commoned......I found continuity between ALL the output terminals.... COM COM V+ V+Is this a SMPSU thing? (I'm old, consider switchmoded and PWN tech to be voodoo, and strangle people who smugly lie about how SMPSUs don't output audio range subharmonics)Or is the meter drinking from a smoothing capacitor somewhere?Or have I bought a small, short, fireworks display that creates its own darkness if used indoors at night?

author: kjr18
author_rank: Regular Contributor
timestamp: March 16, 2020, 07:11:45 pm
content: Unless you really want all the brightness they can offer, you could try lower supply voltage. I once made a x-mas ornament with like hundred of them. At first I thought what monster of a power supply I would need. Finally I settled on one Philips branded usb charger, that was like 2A max, and it worked like a charm. With some voltage drop on usb lead was enough to be blindingly bright and not much power consuming. And those little bastards are good with lower voltages, even like 2,5V, but obviously they barely light up. But still work.