RGBW led lighting - Page 1
Forum section: electronics / projects

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 02, 2013, 01:42:55 am
content: Hey,I'm looking at cheap possibilities of getting a powerful and versatile lighting panel for my living room. I'm thinking some kind of RGBW led setup would be cool, as I'd like to be able to set up custom colors and/or temperatures of white. That color therapy relaxation thing that they do in infra saunas would also be a nice addition, with the slowly shifting colors.I'm wondering, what would be the best choice for the controller? Should I get some WanHungLo "wifi" controller from Alibaba / Amazon market, or is it worth building something?Also, how should LED devices be sized? I have no idea how much light a 12W string of 12V RGB or white LED modules would generate. I'd like the light to be at least equivalent to 3-4 100w incandescent bulbs.

author: IanB
author_rank: Super Contributor
timestamp: December 02, 2013, 01:49:51 am
content: Quote from: Sigmoid on December 02, 2013, 01:42:55 amAs a starting point, look at the lumens per watt figures. Similar lumens will give similar light output.

author: Psi
author_rank: Super Contributor
timestamp: December 02, 2013, 03:00:00 am
content: Yep, i've done this myself. A normal 100W incandescent lamp is around 1500-1700 lumens which is good for a typical room.When i did my LED setup LEDs weren't quite as efficient as they are now. I needed 30W of white LEDs to get that 1700 lumen output.I think now you can do it with ~20W.The cheapest controller is just a mcu/ardunio and 4 mosfets (for RGBW)It's cheap to just use high wattage series resistors to limit the LED current, and you have a heatsink for the leds anyway so you can bolt/glue them to that. I used thermal epoxy to glue typical 5W ceramic resistors to the side of the led heatsink.Of course you can get a proper switchmode current limit LED controller if you want, it's more efficient.Code the mcu to PWM the 4 mosfet color channels (above 200Hz) and your done.I added extra code to provide IR lighting control, just because it was cool and why notObviously you want to put the LEDs into series strings and pick your power supply voltage carefully so it's only 1-2V above the total LED string voltage, that way you limit the wasted power in the resistors.I had more red leds in each string than white due to their different forward voltage but the total LED voltage of each string was close to 13V for each color. (My psu was 13V)As far as mixing goes, i have 30W of white and 10W each of RGB, which is great but probably a little excessive for the size of the room. It depends if you want to just "tint" the white or actually illuminate the room in a pure RGB color, which is always fun.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 02, 2013, 05:49:39 am
content: I wonder what is the best "bang for buck" in terms of LED modules. Any good ones people have experience with?

author: Psi
author_rank: Super Contributor
timestamp: December 02, 2013, 06:12:23 am
content: DX has these 30W RGB emitters for $16 which seem good however i've not tested one.http://dx.com/p/30w-1500-lumen-rgb-led-emitter-metal-plate-39960

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: December 02, 2013, 06:16:53 am
content: I found if you are doing colour mixing, then you often get too much white. The result is a pastel effect for purple, yellow and orange. I think the way to fix this is to use filters over the RGB components. but I haven't tried.

author: Towger
author_rank: Super Contributor
timestamp: December 02, 2013, 06:35:52 am
content: The Chinese '100w' modules you can pick up on eBay, about $20 each. You will need a 36+v PSU, old CPU heat sink+fan, and led drivers. There is eBay seller also in China 'Sure Electronics' who sells 50w drivers which can handle up to 48v with an enable/PWM input. They are about $4 delivered, you could not build them yourself at that price, I'll post the chip they use later. I am replying via phone. You can set the current limit with jumpers. 900ma each is more than enough! Or 1050ma if you want to push... Remember these modules are really 90w.If you want something with lower voltage the try RGBW Cree modules they are 10-12w each, but are about 13+ postage each.

author: Psi
author_rank: Super Contributor
timestamp: December 02, 2013, 07:00:47 am
content: $4 is damn good, don't bother with resistors if you can get a controller for that.

author: Towger
author_rank: Super Contributor
timestamp: December 02, 2013, 09:12:22 am
content: Re the Chinese LED module, I was thinking of this 100W (30Wx3) RGB type, but you can get them separate RGBW 10/20/30/50/100w modules:http://www.ebay.com/itm/RGB-Super-Bright-LED-Light-DIY-red-blue-green-Lamp-Light-10W-20W-30W-50W-100W-/161064759442This is the driver, cheaper if you use best offerhttp://www.ebay.com/itm/150-1500mA-Buck-Regulator-LED-Driver-for-1-50W-High-Power-LED-/161026417634The driver board is based on an Allegro A6211, it appears (black PCB!) to use the reference design and adds extra protection by an additional diode and driving the enable through a signal diode and transistor:http://www.allegromicro.com/en/Products/Regulators-And-Lighting/LED-Drivers-For-Lighting/A6211.aspxBTW these are bright, don't look directly at them...Edit: Fixing links

author: Kjelt
author_rank: Super Contributor
timestamp: December 02, 2013, 09:23:05 am
content: If you want to build everything yourself including the controller go ahead.If you like versatile and expandable lighting controllability make sure your led driver has an DMX(512) input.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 22, 2013, 01:35:10 pm
content: I have one of the 50 watt rgb leds:http://www.ebay.com/itm/50W-RGB-High-Power-LED-Panel-50-Watt-Lamp-Light-/161176213412?pt=LH_DefaultDomain_0&hash=item2586d9d7a4I'm using a 24v power supply. Can someone help me with the resistors? I know how to do the calculations, but can't in this case- red is easy enough- the current is .5A for each channel,and that gives me 14 ohms (at 17V forward V, 7v drop on the resistor).But for the other two colors, i'm not dropping anything, the lowest voltage the specs list that will work is 24V, and that's what i'm using. a voltage drop of 0 volts means a division by zero, do i just not use a resistor here? I've never heard of not using a resistor on an led.I think a simple way to bypass the problem, raise the voltage supply, but it's far easier to find 24v, and also, it would mean more voltage drop for red's resistor, which means a bigger resistor = less efficient, more heat etc..ThanksRob

author: mariush
author_rank: Super Contributor
timestamp: December 22, 2013, 03:34:20 pm
content: For such a power led, you really shouldn't use resistors... you'll dissipate a lot of power in the resistors, heatsing them up and so on.It makes more sense to use a led driver for each of the colors. For efficiency reasons, you should get a higher voltage and the led driver will limit the current appropriately.For example, get a transformer or power supply that outputs around 32-36v DC and then use such drivers to light up each color separately:http://uk.farnell.com/zmdi/zled7020-zi1r/led-driver-buck-1-2a-sot89-5/dp/1898428You just set the Rs resistor to the value for how much current you want the IC to allow through led and choose the suitable inductor for the current you have. The datasheet explains what to look for.The chip above will probably work with 24v as well, but you may not be able to set the current so high.Those leds on the ebay link are 16w per color, so you need to limit current separately to about 1a for red ( 16w / 16-18v) , 600mA for blue and green ( 16w / 24v)

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 22, 2013, 08:04:42 pm
content: This is the driver i'm using:http://www.ebay.com/itm/DC12V-24V-Max-3A-CH-Output-High-Power-DMX-Decoder-LED-Lamp-Driver-Controller-/160818130517?pt=LH_DefaultDomain_0&hash=item257181ee55From the specs, it will take 12 or 24V, but red on the led needs 16-18v and the other colors need 24-48v. This is how i did it with 10watt leds and a similar driver- the driver had power in and four outputs- one for common, one for each color. The common i hooked direct, and each color went to a resistor first that made the volts and current match what the led/color required.I'm just not sure how i make the current and voltage match this 50w led's requirements without the resistor?Thanks,Rob T.

author: mariush
author_rank: Super Contributor
timestamp: December 22, 2013, 10:47:12 pm
content: LEDs are current driven devices. The voltage specified is just the minimum voltage from which the leds are supposed to light up.The driver does not output 24v, it will output UP TO 24v. You configure the current through the DMX interface and then the driver takes the 12-24v input and gradually increases the voltage until the current going through the leds reaches what you set.So for the RED leds, you know the voltage must be between 16 and 18v and they're supposed to use 16 watts maximum. 16 watts / 18 volts works out to about 888 mA. Now you're supposed to connect to this driver box through the DMX interface, configure the RED channel to 888 mA and the box will then boost the 12v until there's around 888 mA going through the led, which will happen at around 18v.Now, the DMX interface.. it's a standard for lightning. You need some software and a transmitter/controller the software can work with (you plug that in usb or a pci slot). You then connect that driver you bought to the transmitter with network cable or something similar. You then send commands to the driver through the software.Or, you know... get a standalone led driver instead which would allow you to adjust current using a potentiometer or something like that, and forget about this led driver.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 22, 2013, 11:04:22 pm
content: Yes, i have this working with 10watt leds on a different dmx driver:http://www.holidaycoro.com/27-Channel-DMX-Controller-for-RGB-Lights-12v-DC-p/24.htmIt works great as i have it set up, i have each of the R G B and B going to a resistor that brings the current to where it needs to be, and the common hooked direct. It works fantastic.The 50W led needs different power supply and resistors. Red isn't a problem, though according to the specs, red needs 500mA max not 888 (or is the spec wrong? I've seen that on some of these generic leds), and with 24 volts going to the controller, it means (1) 14ohm resistor at 3.5watt (call it 5)But my question is for the other two colors. They call for 24 volts minimum, and the controller calls for 24 volts max. If i feed 24 volts into the controller, here is how i calculate what resistor i need:Vfwd = 24vI=.5 (500mA)I calculate the amount of voltage drop (Vd) on the resistor by subtracting the supply voltage from the required voltage for green or blue which are both 24v, so for example, blue:Vd= 24V supply voltage - 24V required for blue = 0vto calculate resistance it's:R=Vd/Iwhich is:R=0v/500Mawhich isn't possible.I hope that was clear, i used to work with ohms law a lot but it's been awhile.. So i was hoping to find out what should i do to make it work? I can't increase the supply voltage since it's the maximum the driver will allow. I can't lower it since it's the minimum the LED needs to operate. Leaving it as is gives me a mathematical problem of trying to divide 0 by 500mA.Thanks again

author: Psi
author_rank: Super Contributor
timestamp: December 22, 2013, 11:18:45 pm
content: Quote from: RobFromEarth on December 22, 2013, 11:04:22 pmIf the LEDs forward voltage min is 24V and your controller max output is 24V then unfortunately you cant use that controller.The max controller output voltage isn't enough to run the led, as evident by the calculation giving a 0 volt difference.

author: mariush
author_rank: Super Contributor
timestamp: December 22, 2013, 11:28:35 pm
content: Quote from: RobFromEarth on December 22, 2013, 11:04:22 pmFrom the ebay page:This is a high power RGB LED capable of outputting16W per channel, total 48W. High power RGB LEDs are in one aluminum backed package. The product is packed in sealed anti-static bag. Do not look into the light.DC Forward Voltage (VF):Red 16-18V;Green 24-28V; Blue 24-28V.DC Forward Current (IF):1500mA16 watts @ 16v = 1A .. .16 watts @ 18v = ~ 888 mA16 watts @ 28v = ~ 570mA

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 22, 2013, 11:38:02 pm
content: It indicates 1500mA, which would be 500mA for each. I didn't see where it said 16W.I guess i still don't understand, if the minimum operating voltage for blue and green is 24v, and the input voltage is 24v, how is that not enough to work? I'm sure there will be a certain mA lost as heat in the controller, but the volts will still be the same (i think?).Thanks

author: Psi
author_rank: Super Contributor
timestamp: December 22, 2013, 11:39:48 pm
content: Sorry, i deleted my post before.I wasn't really sure and didn't want him to blow up his leds with 1.5A if that wasn't correct.The voltage ranges are because the led forward voltage at spec'ed current changes with temp.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 22, 2013, 11:41:41 pm
content: I saw it, but thanks. I did think it was 1.5 per channel when i got it, because it shows as just 1500mA without specifying per channel or overall.

author: Psi
author_rank: Super Contributor
timestamp: December 22, 2013, 11:44:21 pm
content: 1.5A is not crazy high, some high wattage LED arrays take 3.5A per channel.You could connect up a powersupply in current limit mode and check what sort of current the leds draw inside their spec'ed voltage range.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 23, 2013, 12:18:17 am
content: Yeah, i've seen that, would be fun to have one of those working, but i figure i best stick to lower power devices until i can make it work. I'm surprised that 50w is a problem, it seems to be all the same as 10w LEDs mathwise, if i can just figure out how to make it work. Each of the two channels G and B require 24volts min, controller will take 24v maximum input, how to calculate the resistors when it results in dividing 0? The voltage drop across a resistor would be 24-24=0v, so to find the value of the resistor, it's r = Vdrop/amps, so r = 0/.5 (500mA), which can't be done.

author: Kjelt
author_rank: Super Contributor
timestamp: December 23, 2013, 01:47:19 pm
content: Quote from: Psi on December 22, 2013, 11:39:48 pmCorrect but I thought also with age ?

author: Kjelt
author_rank: Super Contributor
timestamp: December 23, 2013, 01:58:46 pm
content: The forward voltage of a led increases by: Current and I thought also Age.The forward voltage of a led decreases by: Temperature.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 23, 2013, 04:58:00 pm
content: Quote from: RobFromEarth on December 23, 2013, 12:18:17 amHey rob, I'm not sure how much money you have, or want to spend, but for me personally, $20 for a dmx controller is dirt cheap, i'd try feed the controller like 26v see if it does anything.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 23, 2013, 08:39:12 pm
content: Yeah pete, i was thinking the same exact thing, i'm anxious just to see what this 50w led can do. But i need to use these for lighting in a public place eventually, so doing it in a way that's safe is important too.I'm just surprised, there are a lot of really knowledgeable people here, maybe my question was so stupid that noone wants to stoop that low. I just can't get past it with my small mind- the colors blue and green need resistors to limit the current, yet with the numbers, ohms law suggests i use a resistor of (0/5mA) = 0 ohms which doesn't make sense.Psi said, "If the LEDs forward voltage min is 24V and your controller max output is 24V then unfortunately you cant use that controller." It's that simple, it can't be done?btw pete, if you know of other dmx controllers can you send a link or two? I know about the "ray wu" one, which is the main one i've been using.Thanks

author: Kjelt
author_rank: Super Contributor
timestamp: December 23, 2013, 10:26:24 pm
content: Quote from: RobFromEarth on December 23, 2013, 08:39:12 pmThat is because you are doing something that you should not do and multiple persons have already told you so, even worse the ebay link for the 50W leds you provided even say very clearly that you should use a 33V driver. Why ? Because the green and blue ledstrings can have a forward voltage of 28V and there should be a margin. Sorry if I am a bit blunt but it seems that you put your head in the sand and don,t want to hear what everyone has already told you: you have a mismatched driver for that led, it does not work. Putting 30V on the driver might blow the driver up (why would it be saying max. 24V other wise?). A solution would be to short out two of the blue and two if the green leds in the RGB array to drop the forward voltage by 6 V but I don,t think you can do that easily with that 50W ledarray.And to answer your question, the resistor is there to dissipate the rest of the power, so for a given current the driver voltage minus the led forward voltage should be falling over the resistor. If your led forward voltage needed is 24V and the driver voltage is 24V indeed you do not need a resistor since no overvoltage should be dissipated, but if your led forward voltage is even 24,1V you have no light at all that is why a led driver should have a decent margin on the led forward voltage so it should be at least 30V.

author: Corporate666
author_rank: Unknown
timestamp: December 23, 2013, 11:06:16 pm
content: Quote from: RobFromEarth on December 23, 2013, 08:39:12 pmThe forward voltage of an LED is not an unchanging thing. It varies with many factors including manufacturing tolerances, temperature, age and lots of other things. Also, there is not a linear relationship between forward voltage and current... a tiny amount more voltage will produce a massive amount more current when you are already in the operating range of the LED.Think of it like a water pipe connecting a water source and a water exit... you are cutting a hole in the top of that pipe to attach your device (LED). If the water pipe is not full, you won't get any pressure at your hole. So if your 10cm water pipe flows 1000 liters per minute and you feed it with a 1000 liter per minute source from a 10cm pipe, you have parity... if there is a tiny tiny dip in output from the source, it means your feed water pipe won't be full, hence no pressure at the hole you cut to power your device.So what you need to do is have more water and water pressure available than you would need, then you regulate it somehow - crudely with a resistor, or correctly with some sort of LED driver. And when you always have more water available from your source than your LED water pipe can flow, it means that LED pipe will always be full and there will be a known amount of flow and pressure at the hole you cut (aka voltage and current).Since the volts and amps of the LED are not constant and will change based on many factors, driving it with a power supply whose max output is equal to the LED minimum input is a bad idea. At best, it will be erratic and fluctuate in brightness a lot with temperature. At worst, it won't work and will likely kill your power supply or your LED. That's why your math isn't working out - you are trying to determine what size baffle or restrictor nozzle you need (resistor) to control flow between a source (power supply) and exit (LED pipe) where the exit can take all the source can provide - therefore no restrictor/baffle is needed mathematically, but realistically it is, because there will be fluctuations in LED drive level/voltage/current and power supply output.Also, I have some experience with those RGBW LED's... you mention using them for a public place? The light quality is beyond crap. Those LED's are crap. They use junk dies, the thermals are terrible and the LED's don't last. It might be OK for a workshop, but if this is some sort of commercial project, I would run for the hills before giving those giant Chinese RGBW LED's any consideration.

author: remixed123
author_rank: Regular Contributor
timestamp: December 24, 2013, 03:39:31 am
content: Quote from: Sigmoid on December 02, 2013, 01:42:55 amThis device isn't real wifi, you will need to connect to it directly, it does not work as part of your wifi network. This makes it very annoying, as every time you want to do something with your lights, you need to change the wifi networks on your phone or computer. And when you do this, your phone or computer no longer has access to the rest of your machines or the Internet.My product (LightServer) gives you what you are looking for, plus lots of other features, but it is not on the market yet (sorry) -Glenn.

author: Kjelt
author_rank: Super Contributor
timestamp: December 24, 2013, 11:23:31 am
content: Quote from: RobFromEarth on December 24, 2013, 08:02:06 amNo it is not but there is a special forum topic beginners for that, and you didn't post there so I assumed you had experience but were too stubborn to listen to the people telling you that the driver was not suited for that led. If it was in the beginners section I would have been more forgiven, so sorry for that.I would also read the comments of Corporate666, I didn't want to upset you more but those leds aren't really very good indeed. Its not your fault to not know that, but Chinese marketing seems to be more about the power (W) then about the quality.If you look how pro companies do RGBW ledlamps and open them up you see a pcb with a lot of independent R, G, B and W leds all about 1W and then 8 or more per color. They are scattered around the pcb and then above is another diffusing plastick disk to make the independent colors "flow" together to mix to one color (light mixing chamber). But then that is another project.

author: RobFromEarth
author_rank: Regular Contributor
timestamp: December 24, 2013, 08:52:37 pm
content: I'm not a beginner, and it's not a beginner's question.I did read Corporate666's comments, thanks for taking the time to write, Corporate666. Sometimes too busy and maybe have a little attitude, sorry if that came off harsh. I spent a ton of time looking for info over the past year or so, and the searches led me to this thread in particular, the subject seemed directly related so i posted here..As far as led quality, The light output varies from batch to batch, colors aren't exactly the same, have had a few go out after running just a few mins (on half the rated current), etc etc, but they're cheap it's worth using them to get this system running, that's the decision i made.