I know this is a while after my last post, but i just wanted to ask a quick question, if i use a 24v power source this doesn't change much apart from the number of LEDs there can be in series and the resistor ratings does it? i want to cut down on the number of LM317 chips, so i thought higher voltage, more LEDs in series, less LM317 chips.
any help would be greatly appreciated

 

That's right, and it's the way to go for large strings of LEDs.

 

My Christmas tree LEDs have so many LEDs in series that I gave up counting them all.
They operate from 120VAC.

 

Final set of questions, im looking for a 24v power source now that converts AC to DC. What i dont understand is how do i determine which power rating I need? do i just add up each components power dissipation? And how do i determine which output current to use? i think i'm just confusing myself now.
help would be greatly appreciated

 

The wattage and current ratings for power supplies are somewhat interchangeable through Ohm's law and the power law. If I have a 24V supply that's rated 50W, I can calculate it's current capacity as ~2A. Conversely, a 24V supply that's rated for 3A would be a 70W supply.

Since you're using linear current regulators, you have to keep all series strings of LEDs to 21V or less but to calculate your current requirement just add up all string currents. If you want to convert that total to a wattage, multiply by 24.

It's a good practice to derate your supply requirements to make allowance for temperature rise, manufacturing variability and "optimistic" specifications. A derating factor of 25% or more would be good so if you need 2A, get 2.5A or 3A.