Mine are also still fine but I only use them a couple of hours a day and I glued them on a aluminium rod. They also stopped to stink.
I hate the bluish colour, If I had to do it again I would probably use some of the 12V LEDs, these have much nicer colour temp. So I have laying around about 1.5m without use…
New to the forum, just found this! I’m an amateur LED enthusiast that last year made a go at turning this knowledge in to products. I started with high quality cree stuff and hand assembling my own circuit boards but am ever intrigued by the cheap Chinese light strip product as it is super cost effective for $/lumen.
Yes. Tieing the back to the front will get you even voltage across. That is how super regulated power supplies work. You bring a wire from the far side back to a voltage input on the supply and it automatically adjusts so that it accounts for voltage drop over the wire. Voltage drop over distances will happen. I haven’t studied this on a lot of the strip light but will look in to. It is a real phenomenon but dont know how drastic it is in this case. Wiring up to the strip with 18ga or bigger will definitely help for higher current draws of your whole system because that will be a choke hold.
Things I’ve done before if there’s strips side by side is pull the plus and minus from strips nearby in the middle so that even if there is voltage drop its from the middle and not the ends so the light doesn’t look increasingly dim from left to right or top to bottom if you’re going in one end and out the other.
I’ve bought the eBay and DX stuff that doesn’t come as described or isn’t the same twice. Amazon has some cheap reels but I feel like that is blow out product and when they’re out they’re out and you never know how accurate their specs are.
I found a great Chinese vendor at a trade show that makes super high quality strip light (they only sell business to business). I’ve bought multiple samples from them and the quality has been super high and lumen output is very high. They provide light files and everything.
Anyways quality stuff is out there its just hard to know what is good or bad on a website. I would say if something doesn’t give you Volts, Amps, Lumens, and Color Temp then stay away. These are specifications every person making a LED product should know even if its theoretical from data sheets. A lot of strip light on websites if it does have lumens don’t tell you if that lumens is for the reel, per meter, per foot, per cut strip or what.
I like to look at total lumens when comparing products. It is the most simple and is the easiest to compare what you’re paying for. I believe some manufacturers use lux (lumen per square meter) ratings though for incandescent equivalents. Go to Home Depot’s website and look at a Cree A19 and Cree BR30. A19 is 800 lumens and 60W equivalent and the BR30 is 650 lumens and a 65W equivalent. How could it be less lumens but a higher equivalent? I use incandescent wattage x 15 lumens/watt and then compare to what my LED total lumens are.
I launched a kickstarter this month for a 12VDC light that uses 12v product from the vendor I spoke of earlier as the light engine and I corded it with a car plug. I’m making the housing. I am including a wall adapter for a car plug so you can use it indoors. Its 300 lumens in 11”. Really bright for tape light! Tape light that has to have a heat sink.
https://www.kickstarter.com/projects/1749518521/mount-anywhere-led
Anyways check it out or support the cause for one if you’re interested in seeing the tape light and how cool and finished a product you can make from it.
I’ve got some experience in this if you want to ask me questions.
[quote=lightvision1A19 is 800 lumens and 60W equivalent and the BR30 is 650 lumens and a 65W equivalent. How could it be less lumens but a higher equivalent? I use incandescent wattage x 15 lumens/watt and then compare to what my LED total lumens are.[/quote]
BR/PAR lights are reflector lights and you lose quite a bit of output there. LED equivalents don’t have the reflector losses but do have losses in their optics.
Also, a better number for USABLE incandescent output is 10 lumens/watt. Most decent LED bulbs deliver 50-60 lumens/watt once you get all the losses figured in… larger sized bulbs are usually more efficient than the smaller ones.
texaspyro, or anyone else willing to weigh in… I’m looking for recommendations for power supplies for these bad boys. I’ve got a 5m strip of 5630 WW leds that I’ll cut into appx. 4’ sections (75 emitters). These will be used outdoors (under canopies, so not super-exposed), so would like a tidy-ish box as opposed to a harvested PC power supply.
It seems like 1.25m wants 18 watts… does that number fit your experience? And wattage-wise, are the specs of transformers on ebay kinda like the chinese lumens problem? Should I shoot for a bit of headroom? These aren’t going to be in 24/7 service, but I really want them to run all night without failure.
You might look into using something like a regulated wall-wart or laptop supply. My dining room table (Replacing Lumiline light bulbs with LEDs) used 10 meters of strip and draws around 6 amps on high. I needed around 14 volts to overcome wiring losses and used an efficient 15V power supply adjusted down until the “bulbs” saw their rated 12V.
When driving longish pieces of strip you need to feed the “+” voltage into one end of the strip and the “-” into the other end. Otherwise the LEDs on one end will be overdriven and those on the other end will be starved for power.
I used a 12V power supply I bought from a shop which sells cheap electro parts, which they buy in large quantities. It’s a small black box like a laptop power supply and I mounted a DC socket on the strip to plug it in.
My strips are only one meter long and I fed them from both sides because even on this small distance I saw a to high voltage drop. Check post #20 for my current measuring.
It works but if I had to do it again I would do it like Tp recommended and tweak the max out of it.
There are tons of nice DCDC step down modules on ebay, one of this and a laptop power supply might work well.
Thanks for the info.
As a total side note, Werner, I suspect that the 72w number refers to the entire 5m string. Of course, finding accurate numbers on ali/ebay/ft/etc is ridiculously hard.
BTW, I was testing a strip while it was still on the reel… it melted the reel rather quickly.
That’s incorrect. Such driven strips have minimum of voltage in the center. So driving the strip from opposite sides allows to double LED strip length. No more.
Is that true? It seems to me that if you examine the total trace length for any single LED placement in a strip driven that way you’ll find it to be the same as any other single LED. Thus the same voltage drop for each, no?
No, voltage changes between segments even if connection wire resistances are equal as currents in connection wires are not equal.
Assuming the strip has the same size conductors on each side, driving it from each end (positive on one end, negative on the other end) causes each led to see the exact same voltage no matter where it is in the strip. The total length of conductors to each LED will be the same.
Note that most strips do have slightly different sized conductors on the positive and negative sides. There is no perfect place to drive them from, but driving from each end is about the best you can do. You gotta work with what ya’ got.
Yep but as always it was Totaly overrated…or at least wrong rated with 12V and 72W. I see most of the time that Chinese label things with the biggest number they can find for a electronic component without mentioning the circumstences correct…
To drive them from both sides is the best if you have a given non adjustable power supply, I guess that is what Eugene is referring too. On the other side, if driven from both sides the minimum voltage is in the middle so it’s totally mixed up what he said…
No! if driven from each end, each LED sees the exact same voltage since the total wire lengths to each LED are the same.
Lets say the strip is 5 meters long and the strip is connected with + at one end and - at the other. The right most LED has 0+5 meters of wiring. The middle LED has 2.5+2.5 meters, and the left most has 5+0 meters. Total length at any LED position is 5 meters so each LED sees the exact same wiring losses (assuming the wires in the strip are the same size).
No. This would be correct for one or two working LEDs in strip. But not for three or more.
Indeed each LED sees equal length of copper from ends. But according to Ohm’s law voltage losses depend not only from wire resistances but from wire currents also. And currents are sums of currents of different LEDs and depend on position in the strip. Most of current flows through positive wire on one end and through negative wire on another.
Draw a simple network with three LEDs in line each sinking equal current for simplicity and four equal resistances connecting them into strip and you will see the voltage drop on the middle LED (current source) is less to the voltage drop of side LEDs.
U2 = U1 - 2I*R + I*R = U1 - I*R
U3 = U2 - I*R + 2I*R = U2 + I*R = U1
I can add that for linearized network currents sinking by LEDs are proportional to cosh(x/a) where characteristic length ‘a’ is equal to 1/sqrt(R*s), where R is strip wire resistance (sum of both wires) per unit length, [Ohm/m], and ‘s’ is differential conductivity of all LEDs in strip connected in parallel per unit length, [S/m]. If you see N soldered resistors per meter each of r Ohm then approximately s=N/r. Position where x=0 must be chosen on the dead end of strip if it is driven from one side and in the center if the strip is driven from both sides and have wires of equal resistances.
For my LED strip I’ve received from China a few days ago the characteristic length a=2.6m so I can not use it in cuts longer than 2 meters even with both sides driving (or 1m with single side driving) if I do not want to see significant degradation of LEDs brightness.
I think there are 2 factors that greatly simplify the circuit. The circuit for the strip LED’s and the resistance in the strip wire screams for Nodal Analysis. However, because the LED’s are diodes, current only passes in 1 direction through them. That means in those nodes, the current flowing in each LED does not have multiple components. That and the fact that the complicated circuit is completely symmetrical, I think this may reduce to the circuit as described by TP.
This is a very interesting problem and I will study it more.
After thinking about this more I realize I’m not just a little rusty, I’m rusted shut! 
It seems now to me that there is no effect when there are 2 LED’s, at maximum when there are 3 and gradually approaches no effect as the number of LED’s increases……….
One experiment is worth 1000 opinions… so just do it. Find a decent LED strip (i.e. positive and negative conductors are well matched… you’ll need a good milliohm meter with kelvin connections to verify that) say 5 meters long.
Drive the strip from each end (+ to one end, - to the other). Then go down the strip with a volt meter and measure the voltage at each LED group (it’s ok to get lazy and measure it every foot or so). Report your results.
My strip has 150 ohm resistors in series with each set of 3 LED’s which are in series. Each of those set of 3 are in parallel. I think this is typical of how these strips are made. That relatively high input resistance of each set of three LED’s effectively simulates each set of 3 LED’s having its own constant current source. Current limiting resistors not only mute the effect of raising the voltage, but also mute the effect of lowering it and the voltage at each node will be almost identical no matter what. That’s why these strips are wired this way and it is also why you would need a very high resolution volt meter to detect any difference.
But you know that. 
If you would want to be able to run longer lengths of these LED strips, then the buss voltage could be increased along with the proper increase in the current limiting resistors.
I believe Eugene is right when he explained this, there is an extra I*R drop on the middle LED. And it seemed that it would make less and less of a difference percentage wise as the number of LED’s in the strip increased.
Just to clarify what I wrote here.
Certainly as the string of LED’s gets longer, the buss will load and the LED’s will get dimmer. What I am referring to is the difference, if at all perceptible, between the center most LED’s and the outer ones. As the string gets longer, the difference percentage wise will become smaller and smaller.
More and more. Let’s N LED segments in the strip sinking equal current.
U2 = U1 - (N-1)*I*R + I*R = U1 - (N-2)*I*R
U3 = U2 - (N-2)*I*R + 2I*R = U2 - (N-4)*I*R = U1 - (2N-6)*I*R
and so on.
For long strip it’s easy to write a differential equation for linearized network and get answer what LEDs current (i.e. brightness) is proportional to hyperbolic cosine of LED position as I explained before. Hyperbolic Cosine -- from Wolfram MathWorld