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I am trying to build a high power RGB LED light. I am looking for 50W-100W range for the LED (all colors combined). 100W RGB LED desn't seem to exist so I am left with 50W, 60W, or 90W options. I would prefer higher wattage single LED module as it's cheaper than multiple lower wattage modules.

There is a suitable 90W LED module. There is no datasheet only this spec:

Voltage: R: 20~22V; G: 32~34V; B: 32~34V; Current: R: 900mA; G: 900mA; B: 900mA; Product size: 45mm x 51mm; Power: 90W; Wavelength: R: 620~625nm; G: 520~525nm; B: 460~465nm; 10 series and 9 in parallel;

I heard that for LEDs in series/parallel you need some additional components for current sharing etc... Do these LEDs have the required circuitry built-in making them essentially the same as a single LED in respect to powering them? Or do I need a special LED driver to power this module? Reason I am asking is because most LED drivers don't mention any specifics about series/parallel LED but I did recently see an LED driver with PWM control that specifically mentioned it's application was for LED module 1 x 50W multichip(10 Series x 5 Parallel). Does this driver have special circuitry or is it just a suggestion for what it can be used?

What do I need to look for in an LED driver in general other than constant current, min/max voltage range and power rating to be equal or lower to that of the LED. (For the 90" RGB LED, each color would use it's own 30W driver).

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  • \$\begingroup\$ Modules will usually claim to be balanced enough to power all strings of one colour together. For optimum LED lifetime it would be wise to measure strings to see how well balanced they are. CC per string can be done with eg LM317 + 1 resistor so cost not too bad. Even a series resistor added per string helps balancing. LED strips have resistors inbuilt but modules usually do not. | You cannot 'just parallel' eg Red with G or B (as youknow). You MAY be able to parallel G & B but best to use own CC for each. Note that lumens'/ Watt change with colour so you may need to adjust currents ... \$\endgroup\$ – Russell McMahon Jan 16 '14 at 17:48
  • \$\begingroup\$ ... to achieve colour balance | What is the application? | You say you need 100W BUT the very best LEDs will give more light at 50-870W than el cheapos at 100+ W. Best eg Cree LEDs run in 5w-10W range each at over 150l/W in some cases. Say 20W /colour = 2 to 4 (maybe 5) LEDs' colour. \$\endgroup\$ – Russell McMahon Jan 16 '14 at 17:50
  • \$\begingroup\$ So essentially I can treat it as one LED? What sort of life reduction are we talking about here? eg. 20% I can live with in favour of simpler design/less components. With 90W LED I was considering each color is 10 series/3 parallel, can I power it as one led with no additional circuitry (just CC driver)? Application is an RGB light (effects with arduino PWM + white/warm function for normal light). Can you recommend a good led for my purpose? \$\endgroup\$ – DominicM Jan 16 '14 at 18:14
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If a module has only two terminals, but has some parallel LEDs internally, you can probably assume there's something inside the module to balance the current between each parallel circuit. This is made somewhat easier when all the LEDs are in one module because they can share a heatsink, and thus the temperature of each is likely close, and temperature variations are a big factor in why parallel LEDs will not share current equally. Each LED was also likely manufactured at the same time, so have very similar characteristics, which you can't guarantee when taking discrete LEDs out of a jar. The module may also include some small resistance in each parallel circuit to help balance. Point being: assume the manufacturer has taken care of this, and all you need to worry about is supplying the correct current to the two terminals provided by the module.

Your particular module is really like three modules, one for each color. It looks like there is one common terminal on the bottom, and three separate terminals on the top, one for each color. I can't find a datasheet that specifies if the cathodes or the anodes are common, so you may have to figure it out for yourself. It looks like maybe you can cut the common terminal apart if you want, but again, I see no datasheet, so you might have to experiment for yourself.

There is no special kind of LED driver that can drive parallel LED circuits. If an LED driver's job is to pump electrons, there's no way for it to tell some electrons to go down one circuit while telling others to go another way. The electrons decide which way to go by going whichever way minimizes their potential.

So, what you want to do with this module is power each of the R, G, and B sub-modules with a suitable driver (or if you can find it, one box that actually has three drivers in it). What you don't want to do is try to put the R, G, and B sub-modules in parallel and drive them all together. Since each color has a different forward voltage, this won't even remotely work: the color with the lowest forward voltage (red) will take very nearly all the current and all the power, and possibly be destroyed. At best you just won't get the other colors to light.

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  • \$\begingroup\$ That clears it up! None of the led modules list lumen output (on dx.com) but if lumen output is similar to that of white led's tehy have its at most 100 lumens per watt. Do you have any RGB LED in mind that can do better? Problem I have with my project is the lack of suitable driver for the red color as voltage range is lower to taht of most drivers especially the few PWM contolled ones... \$\endgroup\$ – DominicM Jan 16 '14 at 19:11
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    \$\begingroup\$ @DominicM I don't think lumen/watt figures are typically given for monochromatic sources because it doesn't make much sense. If you look at the definition of "lumen", it is a power integral weighted to the sensitivity of the human eye, which is most sensitive to green, and least sensitive to red. Thus, a green LED will give you better lumen/watt than a red LED, not because it's more efficient, but because it looks brighter. What you really care about for monochromatic sources is radiant flux per watt, which would be watts/watt, or a dimensionless number. \$\endgroup\$ – Phil Frost Jan 16 '14 at 19:21
  • \$\begingroup\$ @DominicM regarding finding a driver for the red LEDs, I'm not sure what to say but to keep looking. You could conceivably add a resistor to increase the forward voltage of the circuit at 900mA. Of course, that would also really reduce your efficiency. You might try looking at well known manufacturers like Lutron. The cheap stuff you find on the internet is usually cheap because there's a factory in China that makes that one thing in vast quantities, and if it's not the thing you wanted, well, too bad. \$\endgroup\$ – Phil Frost Jan 16 '14 at 19:26
  • \$\begingroup\$ That's a good point. btw Lutron doesnt seem to have any drivers only pre-built systems at least they don't list it on their website... \$\endgroup\$ – DominicM Jan 16 '14 at 19:38
  • \$\begingroup\$ @DominicM they do have LED drivers. Example: lutron.com/en-US/Products/Pages/LEDDrivers/Hi-LumeLED/… I haven't looked at it in detail to see if it would work for your application, but they do, in fact, make just drivers. \$\endgroup\$ – Phil Frost Jan 16 '14 at 19:40

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