Originally Posted by Haggar
Yeah, unless you want to run them at much less than full power, or risk damaging them, using resistors for high power LEDs is not recommended. Its a fine method for small LEDs, though.
The issue is that every LED has a different voltage drop across it, and that drop will vary based on several factors, including temp.
The way to run them is a constant current source. What you can do, is put them in series, as many as practical.
For OEM designs, we run 2 whites in parallel, because we need to run at 9 volts. On a wheeler, Honestly, if the voltage is below 12 volts, then I have other issues..
So, I run 3 whites in series. Then I use an adjustable linear regulator configured to create a constant current source. Cheap and simple.
Ever consider a buck converter?
I've designed circuits at work that power 22V worth of LEDs on 9V.
Admittedly, you don't get AS much current as something that has the voltage to back it up without the buck, but it's another thing to consider.