power supply for a ws2811

Using Arduino General Electronics
#1

Ey guys!

I would like to expose my experience trying to feed a 150 Leds ws2811, that I want to test with Adafruit´s strandtest.ino

the strips specs are:

5M / 150 RGB LEDS WS2811 IC control 3 LED Chip Work Voltage: DC12V Work Current: 3A

http://www.ebay.com/itm/281261795832?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

I am testing the strip with 2 different power supplies.

1 (12V / 1200mA / 14.4W). It seems to be reading the information correctly, but not all the Leds react. This power supply is obviously not enough to feed the strip, that requires 36W / 3A

2 (12V / 5A / 60W). This power supply should be more than enough to feed this strip. Nevertheless, when I connect it, every Led turns on with a bit of red & green. When I trigger the strandtest I see that it is also reacting to this information, but every Led continue being ON with this red & green colour... This is very weird. Should I assume that it is a problem of the power supply?

hope you see the light where I see only confusion!!!

#2

camilozk: Ey guys!

I would like to expose my experience trying to feed a 150 Leds ws2811, that I want to test with Adafruit´s strandtest.ino

the strips specs are:

5M / 150 RGB LEDS Work Current: 3A

2 (12V / 5A / 60W). This power supply should be more than enough to feed this strip.

Where did you get 3A from?

150 RGB LEDs is 450 LEDs. 450 LEDs @ 20mA each is 9 Amps.

You don't want to run a power supply at 100% load so look for a 12A power supply if you intend to turn them all on 100%.

With that much current you should probably connect the 5V at both ends of the strip to prevent voltage loss along it.

Use thick wire and measure the voltage at various points along the strip. If you see voltage losses then make an extra 5V connection to the middle of the strip to prevent it (some people add extra connections anyway to keep the strip from getting hot).

#3

thanks for your intention, but you have everything completely upsidedown.

the strip has 150 rgb leds. 30 leds per meter, 5 meters = 150 leds and not 450.

the strip works with 3 amperes, as you can see in the specifications I posted.

the voltage of the strip is 12 volts, and not 5v, as posted in specifications.

I am anyway interested in what you say about "connecting the power supply at both ends of the strip to prevent voltage loss"along it. " how does this works?

#4

the strip has 150 rgb leds. 30 leds per meter, 5 meters = 150 leds and not 450.

No you have it wrong. Each RGB LED is in fact three LEDs in one package so yes there are 450 LEDs to light up.

I am anyway interested in what you say about "connecting the power supply at both ends of the strip to prevent voltage loss"along it. " how does this works?

It makes reduces the resistance in the wires to the end LEDs.

#5

I know how led works, but specifications states that the strip work at 3A, 12V, 36W, and I need to understand why it doesnt work properly under the circumstances displayed at the beggining of the threat.

here is the datasheet of the strip. I dont know how to read this things. perhaps somebody can find this info? http://www.adafruit.com/datasheets/WS2811.pdf

Regarding "connecting the power supply at both ends of the strip to prevent voltage loss along it". super. can you please clarify how is this done? I mean how do I do the connections, and if you could be more specific with the electronics theory?

thanks!

#6

and it is not the issue of this threat.

So you are threatening me are you. Better not read any more. :P

Regarding "connecting the power supply at both ends of the strip to prevent voltage loss along it". super. can you please clarify how is this done?

Take the red wire from the power supply and connect it to the +ve on one end of the strip. Take another red wire and connect it from the +ve on the other end of the strip and connect it to the wire on the first end of the strip. Do the same for the ground connections.

the point here is that the strip work at 3A, 12V, 36W,(or at least this is what the specifications that the ebay´s seller published)

So link? It is very unusual to have a WS281 in a strip that runs off 12V because the data sheet shows that chip as needing a 5V supply. This would require a voltage regulator on each chip which is unnecessarily costly. So something is wrong.

if you could be more specific with the electronics theory?

If a chip does not get enough voltage it can not work properly. If the strip is too long it will have too much resistance and then there will be too much of a voltage drop across this resistance for the chip to work correctly.

#7

camilozk: thanks for your intention, but you have everything completely upsidedown.

Ah, the confidence of newbies...

camilozk: the strip has 150 rgb leds. 30 leds per meter, 5 meters = 150 leds and not 450.

Nope. RGB LEDs have three LEDs inside them. A red one, a green one and a blue one. That makes 450.

Hint: Light one up at minimum brightness and take a close look.

camilozk: the strip works with 3 amperes, as you can see in the specifications I posted.

There's a simple test: Measure the voltage along the strip.

Go ahead, do it!

camilozk: the voltage of the strip is 12 volts, and not 5v, as posted in specifications.

Nope. If it uses ws2811 LEDs then it's 5V.

camilozk: I am anyway interested in what you say about "connecting the power supply at both ends of the strip to prevent voltage loss"along it. " how does this works?

Wires have resistance, use Ohm's law.

Even simpler: Get your multimeter out and measure the voltage.

#8

camilozk:
regarding the amount of leds, this is senseless and irrelevant.

LOL!

It’s the ONLY relevant detail when calculating the power consumption of WS2811 LEDs.

#9

2 (12V / 5A / 60W). This power supply should be more than enough to feed this strip. Nevertheless, when I connect it, every Led turns on with a bit of red & green.

Yes and if it is a 5V strip then you have destroyed it.

#10

dear mike. thanks for the aclaration about connecting both ends, and sorry for the "threat" :)

I thought I´ve pasted the link for the product and the datasheet:

http://www.ebay.com/itm/281261795832?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 http://www.adafruit.com/datasheets/WS2811.pdf

both the product description in ebay, and the led strip, say that the led strip work at 12V. The strip has the value "12V" printed every 10cm. I think we can all agree that it would be very very unusual that this strip works at 5V if it says 12V both in the strip and the description. And for the "working current" says = 3A. Thus 36W for the whole led strip.

At this point I still just know that I cannot make it work with either power supply that I´ve tried. One because it is not powerful enough, the other one because it simply acts crazy, and I dont get why... I suppose I will wait till I find another power supply...

#11

That ebay advert looks very suspicious. There is a lot about modes of operation which is totally irrelevant. The data sheet shows you can use 12V but only if three RGB LEDs are controlled at any one time, so they are not individually addressable. The data sheet shows 18.5mA constant current drive so for 3A then that would be 162 LED elements or 54 full RGB LEDs which doesn't add up what ever way you look at it. Unfortunately some far east sellers haven't got a clue as to what they are selling. Your only recourse is to measure what you have with a multimeter. What is the voltage out of your power supply when the LEDs are on and what current is it drawing at that point?

#12

yeah... I thought about it... but if this was true, then the led strip would work with 5V, and it doesn´t. I am testing it with the strandtest.ino from adafruit and it just turn very mildly the leds with a bit of red and that is all. truth be told, I got better results when using the 12V / 1200mA power supply. I saw a nice amount of leds reacting to the sketch, but after 1.5meters, the leds were all off.

I am still very confused, but I think we could start admiting that perhaps this people is building 12V working ws2811??

I dont have a multimeter. I will try to get one. my electronics knowledge is very basic, but I am working on improving it.-

#13

Just FWIW but a 'regular' 500 watt desktop PC power supply "Should" work perfectly and there are a whole bunch of posts here in the Arduino forum as well as many others on the Web... Several 'stores' on the internet sell PCB's and Banana plugs as a breakout board kit just for turning a PS power supply into a rather nice 'heavy duty" power supply. Sparkfun is one and Adafruit another. Most however don't include fuses which are really required for this level of power... Fuses are primarily used for fire prevention as semiconductors will emit that Stinky blue smoke long after the device is toast.. As to connecting the Power ends together... Great IDEA, Mike really great, So is using at least 18 Ga wire to connect the strip to the power supply. I've been an engineer for 40+ years and that Never occurred occurred to me... Not once. It might help to visualise the connection as 2 (for example) 1 ohm resistors. When connected in parallel the value will divide by 2 so in this case you would end with 1 ohm total resistance because the individual resistance Positive or Negative is divided by two and then you must sum those resistances to get the "network" resistance. There is a lot more involved in this case besides a simple parallel resistance issue as the resistance isn't a single part but many smaller parts (pieces of wire, PCB trace thickness's and possibly connectors too) but it does serve to illustrate the issue. I do have to point out that this can only be done with the power wires, never the data line as well. It might also be a very good idea to connect 470 to 1000 uF 25V caps at both ends of the power supply connections, Start/Finish and Midpoint of the power supply leads internal to the PCB's themselves. This is for the small but important drop due to the PCB traces... which likely is where most of the loss is incurred. a few 100 nF caps couldn't hurt either... Cheap insurance for noise spikes...

Doc

#14

camilozk: I thought I´ve pasted the link for the product and the datasheet:

Nope, and that usually causes confusion.

That advert says "1 WS2811 IC control 3 LED Chip". If the LEDs are in groups of three then it will work at 12V and you'd need 1/3 the number of amps to run it.

The LEDs won't be individually addressable though. Color will only be controllable in groups of three LEDs.

If the LEDs aren't working then make 100% sure you connected Arduino GND to power supply GND. If you don't connect them then you can easily destroy the Arduino and/or LEDs.

This can also happen if the wire comes loose. I don't trust Arduino headers much so I solder a wire to the USB housing on the Arduino and fix the other end to the power supply with screw terminals.

#15

great information guys!!

I will read through carefully to incorporate all this details, that as I am starting with all this, I am unaware of.

I will also get a multimeter and check all the details of the led strip and let you know when I have it running!

thanks!

#16

FUNGUS: your advice was the most important so far: THE GROUND OF THE LED STRIP HAS TO BE CONNECTED TO THE GROUND OF THE ARDUINO BOARD. this is the reason why it didn´t work and it works now.

CONCLUSIONS: the strip works with 12V, and I am using a 1200mA power supply so far, which seems to be enough so far. I´ve tried it with the strandtest.ino sketch, the RGBCalibrate from the "fastled" library, and my own sketch.

FUNGUS, you are right again: the strip is not fully addressable. "Color is only controllable in groups of three LEDs".

like always: thanks for discussing!

#17

camilozk:
FUNGUS: your advice was the most important so far: THE GROUND OF THE LED STRIP HAS TO BE CONNECTED TO THE GROUND OF THE ARDUINO BOARD. this is the reason why it didn´t work and it works now.

CONCLUSIONS: the strip works with 12V, and I am using a 1200mA power supply so far, which seems to be enough so far. I´ve tried it with the strandtest.ino sketch, the RGBCalibrate from the “fastled” library, and my own sketch.

FUNGUS, you are right again: the strip is not fully addressable. “Color is only controllable in groups of three LEDs”.

Some good stuff here.

Indeed, there are many 12V strips being used for home Christmas light displays (a friend of mine has thousands of them on his house each season).

For future searches, you can hook up a ton of lights and power them with a small power supply if you limit how many are on at a time. Hook up 300 lights and make one LED run back and forth Cylon-style and that works fine… I did a bunch of testing recently with 120 LEDs (5V) being powered off an Arduino, and I just made my code limit how many could actually be on at any given time to prevent doing damage.

#18

allenhuffman: I did a bunch of testing recently with 120 LEDs (5V) being powered off an Arduino, and I just made my code limit how many could actually be on at any given time to prevent doing damage.

Until a cosmic ray causes the Arduino to crash then they all turn on at simultaneously and burn the house down...

(nb. When doing this be sure to add a fuse. They cost 20 cents...)

#19

which sort of fuse do you recommend, and how to connect it?

#20

camilozk: which sort of fuse do you recommend, and how to connect it?

https://www.google.es/search?q=fuse+holder&tbm=isch

Match the amps to your maximum expect current.