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.