Trying to make a LED Panel (UV Light Box) The Wiring? - Page 1
Forum section: electronics / beginners

author: MistaMun
author_rank: Contributor
timestamp: September 19, 2015, 01:11:19 am
content: Hello! I am trying to make a UV light box but I don't know how to design the wiring!So I just ordered 500 LED so that's not an issue fromhttp://www.aliexpress.com/item/500pcs-Free-shipping-Super-Bright-5mm-Round-UV-Purple-Led-Emitting-Diode-F5-LED-light-for/32341816953.html?spm=2114.01020208.3.19.0IP8OM&ws_ab_test=201526_5,201527_4_71_72_73_74_75,201409_2So like as any diode, I know that there will be a voltage drop for each LED when I put them in series. So does that mean I have to figure out a way to wire all of these leds parallel? I don't know where to start!Please assume that I will use 64 leds for this project.What kind of power supply do I need? How should I wire the leds? Thanks!

author: singapol
author_rank: Frequent Contributor
timestamp: September 19, 2015, 02:48:47 am
content: Normally you would buy a dedicated LED driver power supply which use pulse width control for better efficiency and prolong the life of led by turning on only a fraction of time vs continuosly which generate more heat. Your way would result in a bigger transformer even if series connected. There are plenty of led driver supplies available cheaply.

author: michaeliv
author_rank: Frequent Contributor
timestamp: September 19, 2015, 03:31:20 am
content: The right way to do it is to use an LED driver to drive them using constant current.In practice for this project that would be overkill.Hook them up in pairs of 8 in series and then put multiple pairs in parallel.Then drive them from ~12v using an adjustable boost converter:http://www.aliexpress.com/item/XL6009-boost-module-DC-DC-Power-Modules-Ultra-adjustable-boost-regulator-LM2577-DC-DC/1605337399.htmlYou can power the converter from a 3.7v Li-Ion or from 5v.By controlling the output voltage( via the potentiometer) you can control the brightness. You are looking for a voltage around 25v.This solution would have the disadvantage that some leds would be brighter / dimmer than others, but in practice it wouldn't be noticable.If you're going the constant current way you can get this:http://www.aliexpress.com/item/MAX7219-dot-matrix-module-microcontroller-module-control-module-display-module-finished-goods/1627687118.htmlIt has 64 LED's, replace those LED's with your LED's + you need an arduino to drive it, but you can digitally control the brightness and whatnot.

author: Psi
author_rank: Super Contributor
timestamp: September 19, 2015, 03:49:31 am
content: Quote from: MistaMun on September 19, 2015, 01:11:19 amNot all LEDs labeled as UV on aliexpress/ebay are actually UV. A lot are purple leds.Most people want them for decoration, they just want the UV *look*If they were shipped actual UV leds they would likely complain that they're really dimThose do say 395~400nm, so should be UV. Assuming the specs can be believed.Dont expect to be sent top quality leds at $8 for 500 though. You'll probably want to test them before soldering, some will likely be dead or dimmer than the others.

author: Chris C
author_rank: Frequent Contributor
timestamp: September 19, 2015, 04:03:06 am
content: What  said, but also include a 220ohm resistor in every series chain. Otherwise normal differences in the forward voltages of individual LEDs tend to cause some chains to be brighter than others. It only takes a tiny difference to cause this, if ballasting resistors aren't included.And if you want reasonably long life, adjust the voltage on the boost converter so that no more than 15mA is going through each series chain, or 120mA total. They're supposed to handle 20mA, but that's the maximum; and it's never a good idea to drive anything at the max, much less cheap components.

author: sleemanj
author_rank: Super Contributor
timestamp: September 19, 2015, 04:05:51 am
content: Quote from: Psi on September 19, 2015, 03:49:31 amThese Chinese UV leds work fine for PCB exposure, you don't need deep UV for that.Have made a number of exposure rigs using 5mm leds, as I say, they work, technically (but don't over-drive them at all, and make sure there is airflow otherwise they do tend to die after a few hours, which you might run into doing long exposure of UV curing soldermask inks), but actually aligning them to get a nice even exposure, even with a diffusion layer, is a PITA, not to mention all the soldering. Currently I use eight 1 Watt star type UV leds, instead of at least a hundred 5mm ones, so much easier.

author: Zero999
author_rank: Super Contributor
timestamp: September 19, 2015, 06:42:00 pm
content: Quote from: sleemanj on September 19, 2015, 04:05:51 amYes the shorter wavelengths of the visible spectrum will work. You'll probably find even blue LEDs work.