50 LEDs on a Sculpture - Page 1
Forum section: electronics / projects

author: Factotum
author_rank: Contributor
timestamp: September 16, 2024, 04:24:17 am
content: Scenario - need to mount a 3W LED in 50 different locations on aluminium sculptures with a central power supply.LED Vf = 3.0V, If = 1A. Cable run to each location (average length 15 meters) from central PSU with a resettable fuse or PTC for each run.Proposed voltage supply wither 5v or 12v.Will need to make PCB to hold SMD LED.Originally thought I'd use a 5V supply requiring a 2R limiting resister (dissipating 2W). I figured I'd put the resistor with the LED on the PCB. Mounting point is internal on a 50mm aluminium tube - I can't use fasteners for the board to aluminium mount (can't pierce the art and it's concealed) and it's a curved surface. Thinking a thin / long board if needed and thermal epoxy to mount.On further thought I figured there may be differing voltage drops over the cable runs and perhaps using a 1A constant current driver on the board might be a better idea. Can bump the PSU to 12v.Thoughts, ideas, comments?Potential mounting concept

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 16, 2024, 05:27:05 am
content: How the LEDs are arranged? Do you need to control each LED separately? How much of a factor money/efficiency/modularity/simplicity are for the design? Redundancy?50 separately powered boards if money is not a factor and you want freedom.17 strings of 3 LEDs in series and a resistor/current source imo is the most sensible if you want to stick with 12V. Or maybe 10 strings of 5 LEDs and power it from 18V/19V supply.If you're willing to deal with boost converter or even higher voltage supply, then 5 strings of 10 LEDs. That should be still well within SELV limit.

author: mariush
author_rank: Super Contributor
timestamp: September 16, 2024, 06:02:11 am
content: Use a cheap buck led driver on each pcb board, to lower 12-24v down to 3v - 3.2v 1AThis will allow you to use thinner wires as there's less losses in the wires. Also, optionally you could also adjust the brightness of the leds by adding an extra wire to do send a dim signal to the driver.AL8861 is under 40 cents on Digikey, around 20 cents on LCSC , and the rest of the components needed will be under 30-50 cents, making all under 1$. You can use pwm signal or analogue voltage to set the brightness.AL8861 :https://www.digikey.com/en/products/detail/diodes-incorporated/AL8861WT-7/6702375orhttps://www.lcsc.com/search?q=al886150 leds x 3w per led = 150 watts .... with resistors you'd waste 100w heating resistors.With 12-20v power adapter, assuming 85% efficiency (losses in wires and driver) you'd need at least a 150w * 100 / 85 = ~180w psu... 200-300w meanwell industrial 12-24v power supplies are cheap.Or you could use two separate laptop adapter style 95w-120w power adapters.

author: artag
author_rank: Super Contributor
timestamp: September 16, 2024, 07:58:52 pm
content: If you're using a buck converter per led (not unreasonable with 1A LEDs) you can do better than that. Modify the converter to control current rather than voltage (eg by putting a current-sense resistor in the ground wire of the led and controlling the buck converter for an appropriate - and small - voltage there). Then, you don't waste any power in a current-limiting reistor.

author: Factotum
author_rank: Contributor
timestamp: September 19, 2024, 06:08:34 am
content: That does seem like a good approach.I've got a spare 48v PSU I can modify to drop the supply voltage <40v for that current limiter...