RGBW led lighting

[RobFromEarth]

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

[Kjelt]

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. 

That 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.

[Corporate666]

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

The 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. 

[remixed123]

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?

This 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.

[Kjelt]

Yeah Kjelt, it must be annoying to have a newb ask questions

No 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.
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[RobFromEarth]

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.