If you read My kingdom for a 12V adapter, you know I'm in the process of installing many LED strips in my house. You may find it instructive to look at the couple I've evaluated.
Because I didn't want to spend $50, $100, or more for every 5m LED spool, my strips have all come from China-direct sources. Read on to learn about the issues I’ve encountered.
The biggest problem I found with the two LED strip types I evaluated is that the conductor resistance is simply too high. It's not a big deal if you're cutting the strips to, say, 1m lengths, but using longer pieces means feeding power to a few spots along the strip – not a big problem, as there are solder pads every three LEDs, but a pain nonetheless.
And the higher brightness 5630 LED strip
Note that these are both 12V, 60 LED/m, 5m strips. They consist of 100 three-LED groups: each group is a series string of the LEDs and a current-limiting resistor. Thus, the load is very nonlinear: a small change in voltage results in a much bigger change in current than a resistive load would cause.
V (across resistors, near-end, V)
The key takeaway from the table is the drop in far-end LED current to about 42% of the near-end current when fed at only one end.
My workaround is to attach the 12V wiring to the 5m strips at two or three spots along their length. The ideal two-spot attachment points are at ¼ from each end, making no LED more than 1.25m from a power source, though that will still result in a fair bit of brightness loss. The 5630 strips have wire pigtails at both ends, so they make easy – if suboptimal – connection points. Three connections – 1/6 from each end and the center – would make the maximum LED-power distance 0.83m. Believe it or not, the cheapest suitable wiring I can find is standard 14/2 (AWG 14, two- (plus ground) conductor) AC cable. Cheapest, at least, when bought on a 150m spool.
Despite the low prices, all the strips I bought also came with a little control board that offers dimming and various blinking patterns, and actually works perfectly well, even to the point of maintaining its setting with power off.
The bottom chip is an Atmel 24C02 256 byte EEPROM; the other, unmarked (ASIC or µC). The board seems to be made for RGB given the three transistors and COLOR button, but those transistors are actually in parallel. Go figure. As always, the image is larger than it appears.
About sources: Although I’ve bought quite a few items besides LED strips from the GearBest Website, and was usually happy with the results, I no longer patronize them, given the awful PSUs they sold me, but particularly because they won't print my negative reviews about them. Okay, they're probably not unique in either respect, but there are many other similar sites to choose from. Which do you like?
I’m very curious whether the much more expensive strips from other vendors have the same voltage drop problem I've discovered in the cheap ones. If you have any, please run some tests and let us know in the comments.
“I am also working on an LED lighting project, but I'm using the 5 meter strips with WS2812 3-color LEDs. Like yours, the strip came from China and included a controller, but these operate at only 5V. The spool looks very much like your picture.nnFollo
“In the course of researching RGBW LED strips for accent lighting in our kitchen, I came across some strips that take into account the voltage drop vs position problem. These are current controlled strips, and if you look at the closeup, you can see that
“It surprises me that you can observe a difference in brightness when power is applied at more than one end of the string. The WS2812 does its own constant-current control, so unless your Vdd were sagging to the point of clipping the driver current, I wou
“My experience with these strips involves multiple short runs (u22641m) so I'm not too bothered by voltage drop. My problem is loss of output over quite short periods – of a few months. This seems more due to to discoloration of the plastic (possibly by h
“I'm quite a fan of these lighting strip reels; usually acquire them for ~ 6$ / 5m. I tend to favor the flexible strips with the waterproofing cover; I have not experienced the discoloration that JamesBryant has experienced, and generally prefer the addit
“It seems I have a solution for these strips, Michael, a proper 3R3T ballast for them. n”
“I've had a piece of LED strip in my garage over the winter, and had it crap out with the temperature changes. And a half-meter under my kitchen counters, over a year has had 3 “segments” of 3 in series go out. It's either the LED bond wires or a solder
“I've used a few of the waterproof ones for adding a little lighting to fishtanks. The water-proofing sounds like a good idea but if you run the LEDs close to full-whack, they perish the water-proof coating and then the trouble begins. Aluminium or at leas
“Plus, I *loathe* having to slice away the waterproofing; always worried I'll slice the actual strip, or my fingers, or both….”
“In Indochina we can buy 5 metre and 100 metre lengths – the latter for building and structure illumination. The longer lengths are supplied with plastic piercing clips through which power is fed at intermediate points. If you are buying over 10 pieces th
“Update, Christmas 2017: most of my under-cabinet LEDs have died (usually two out of the 3 in a series string…?) and so I ordered some new ones from BangGood. Zooming in to the photo, I see they use 39 ohm resistors. Hmmm. Mine are: 18 ohm. I've been ove
“Very interesting, thanks… Hadn't seen those quad LEDs before either.nnI should measure the drop on my cheap RGB strip. In its favour, the operating current is fairly low.”
“I take it you're referring to strips with a plastic sheath for waterproofing? Hmm, I hope that doesn't happen to my RGB strip. But my white strips are all naked.”
“Even with a 2:1 or 3:1 current ratio between near and far LEDs, it can be difficult to judge the brightness difference. Measure some resistor voltage drops: you may be surprised. “
“I've fixed one or two wonky “segments” with my soldering iron. Must be LED-free…uh…”
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