5050-3LED

Maybe this will kelp you a little?

I have some of these. There are 20, 3 LED sections to a strip. The entire 20, 3 LED strips (all still connected together, I haven't separated any individual sections yet) operate from about 7.5 to 12 VDC. At about 7.5 VDC they just barely begin to light, at about 12 VDC they are at full brightness. The gray wire is + and White is -.  I am using just an adjustable AC to DC converter as a power supply, no resistors or anything else added.

I just powered them with this for the above test:

AC/DC to DC LM2596 Adjustable Voltage Step-down Power Supply Module + LED Meter

There are other versions of this item available on ebay or maybe Amazon also, without the meter that are much cheaper if you want to go that route. There are also DC/DC converters available that are very cheap if you have DC power to start with.

Added a couple of pictures. The LED's are just starting to light in the first picture, the room lights are kinds messing that up, but turning them off messed up the camera's focusing ability.

Thank you!  I think I finally get it.  The 3 LEDs in each module are in series with a built-in 120 ohm resistance.   The 20 modules in the string are wired in parallel.  I can separate any number of the modules desired and not worry about a proper resistor.  The 20 module string draws 400 mA (20 modules x 20 mA each.) More than one 20 module string could be connected.  The current draw just goes up accordingly. 

If this is incorrect, I will have to tear down my layout and think about collecting stamps.

How did you conclude 120 ohms and 20mA per set of 3

Previously you said the items in your first picture are labeled 910 which generally means it's a 91 ohm resistor.  Hard to see but it looks like there are 2 of them next to each other...probably in parallel.  This would make a 45 ohm resistance and in the ball park of what Fec fan said about 60 mA 5050 LEDs.

Bucky, this is a good site to start your new hobby.

For what this is worth, took some readings using my harbor freight mini clamp on AC meter, probably not exact, but close. The 2 surface small black mount devices have '1D1' or '101' printed on them, using a magnifying glass, still can't see well enough to say for sure. Maybe John or Stan can cipher this for us?

The full set of 20 strips of 3 LED's

 7.5 volts = 0.03 amps

12.0 volts = 1.18 amps

1 strip of 3 LED's

 7.5 volts = 0.03 amps

12.0 volts = 0.12 amps

Since the strips are only using half the power from the transformer unless you proceed it with a full wave rectifier, that would be about right.  Also, the clamp-on doesn't measure true RMS, so the accuracy may be somewhat in doubt.

The 101 on the resistor is the marking for 100 ohms.

The numbers are a bit confusing .  For 7.5V, the current was the same for 1 strip and 20 strips??  And for 12V the current is only 10 times greater when hooking up 20 strips??

If you have a DMM, if you can use the DC-current mode and place the meter AFTER your AC-DC converter module I believe we'll get "better" numbers.  As GRJ points out, AC-current measurements can be mis-leading with a typical hobby meter but DC-current measurements are generally more accurate (albeit requiring you to insert the meter into the current path).

Ahh, but you're not telling them the "secret" code!  For these surface-mount resistors, the 101 is 10 plus 1 zero or 100 ohms.  Bucky says 910 which is 91 plus 0 zeroes or 91 ohms.  Many strips have a 151 resistor which is 15 plus 1 zero or 150 ohms.  And so on...

STAN!  What's wrong with you, we're supposed to have a few secrets.

I didn't even look closely at the 7.5 volt number as I assumed they're all dark at that voltage.

New readings from the DC side this time.

The full set of 20 strips of 3 LED's

 7.5 volts = 0.81 mA

12.0 volts = 0.73 amps (hit 200mA at around 10 volts, had to go to 20 amp scale here)

1 strip of 3 LED's

 7.5 volts = 0.08 mA

12.0 volts = 42.2 mA

The LED's just start to light slightly before 7 volts in the dark. You can barely see them. At about 7.2-7.3 volts you can tell they are starting to light with the room lights on. At 7.5 they are dim, but light up with the lights on in the room. So 7.5 is where you can definitely tell they are on.

And if Stan gives up all the secret info, you guys can finally give your typing fingers a rest. Won't be so many questions from us green horns. But then again we would miss not having your replies to read, may be best to keep just a few.

I really don't understand, I guess.  The LED Wizard is where I got the 120 ohms for the resistance.  But those small numbers on the resistors in the original photo of the module are indeed "910" or, according to the secret code, 91 ohms each. What am I missing here?  It is at least true that the 3 LEDs in each module are in series and the 20 modules in the string are wired in parallel?  I don't understand why the resistance is different than what the wizard said?

In this diagram your statement is correct. 3 are in series and the 20 rows of 3 are in parallel. The strips I have (in the pictures above) appear to be just the opposite. In the picture above, the wires enter one end of each strip, exit the other end of the strip and then go to the next strip. This should be series.  Parallel would be like your drawing, the power feed going up one side of each 3 LED strips and the common going up the other side of the strips. Then the LED's in your drawing are in a row (series), power in one end and common out the other.

I don't know how each strip of 3 is wired internally though? The 2 resistors and the way the LED's are positioned in the strip are somewhat puzzling to me. I may have to sacrifice a strip to see the internals. Or maybe John and Stan already know (they probably do) and if so maybe they will enlighten us (well me anyway).

In your calculator, it appears you specify LED voltage and current.  Here's a datasheet of the first 5050-sized LED that came up at DigiKey.com:

http://www.qt-brightek.com/dat.../QBLP679E-IWK-XX.pdf

In it is the following table with "typical" characteristic of 3.1 Volts at 60 mA.

If you enter these numbers for your array of 60, I think the calculator will spit out a resistance closer to 45 ohms than 120 ohms.  I believe those 2 resistors per strip are in parallel.  And if they are 91 ohms each, in parallel that makes 45.5 ohms. 

Here is the picture of a 3825 strip that led me to believe the LEDs were in series and if subsequent modules were added they would be in parallel.  I suppose there are more than one way to build them.

It does. 47 ohms to be exact. And I am not sure where I came up with the 20mA.  I just looked at the specs for the ones I bought on Amazon and it says 60.  Just proves I don't know what I am doing.

So each 5050 LED has three chips (and each module has 3 LEDs.)  That explains why a 5050 chip is so much brighter than a 3528, for example.  The 20mA I used would only be correct if the LED had 1 chip.  Maybe I am inching closer to understanding and won't have to resort to stamps.  Thank you!  Sorry, y'all have to explain this so many times.

Was re-reading this thread, only thinking a little this time. I believe the drawing you posted and your statement above is correct for the strips also. If the 3 LED strips were in series I think we would be out of voltage after just a few strips of 3. If the individual 3 LED strips were in parallel there would have to be 3 resistors, one for each LED. So I think the drawing from the LED wizard is correct for the strips also. You are correct on the 3528 strip being series also, only 1 resistor. I hope we can get rid of the stamps now.

Stan has to be correct about the resistors in parallel. Yours would be 45.5 and mine would be 50 so that's pretty close. Thanks to Stan for giving up John's secret codes, if I can only remember them.

Hope this makes sense and I didn't add to the confusion with my own above. All I was thinking about last night was the way the wires go in and out of the 3 LED strips, that was confusing me. I'm not going to sacrifice one just yet.

I'm still trying to learn also. I sometimes feel like I'm being a pest also as I don't always clearly understand what the knowledgeable folks are talking about. John, Stan, Dale H and many of the others here are a great help. I'm also glad they are here and put up with our questions.

Me too.  Thank you guys!