DIY LED array

[gconcepcion]

I recently read an article on dealing with LED heat...

http://www.designnews.com/article/45128 ... id=2716411

This might be a bit redundant and basic information at this point, but I thought I would share.

Wow, thanks for the article link. A nice little distraction so I can keep procrastinating this manuscript i'm supposed to be working on...

Pretty much answers my question, i'll be using a fan regardless of whether or not its necessitated, simply for the fact that I may be able to extend the life of the LED's by several factors (maybe even an order of magnitude) depending on how cool I keep them.

The initial expenditure getting this rig set up will be well worth it given the long term costs w/ bulb replacement for HID's or fluorescents. I won't have to replace the lights for a decade, even longer if i'm able to minimize the heat (or conversely shorter if I let them get too hot)

[gconcepcion]

Finally got the heatsink drilled & tapped and the LEDs mounted with screws and Arctic silver 5:


I only sanded up to 1000 grit sandpaper. As per earlier advice I didn't think it was necessary to go any further than that, it's way smoother to the touch then when it was unpacked.

I expected some problems along the way, but was pretty pleased that I encountered no game changing obstructions. I wound up drilling all 72 holes with a my hand drill and a #43 bit and only snapped two of them, one of which is lodged below the surface of one of the holes. Fortunately it was one of the spots where no LED was planned to be installed during this revision.

I did, however learn the hard way (twice), that you should NEVER attempt to tap (tap size #4-40) a drilled hole with a power drill, even at low speeds (DUUHHHHHHHHHHHHH). In retrospect, makes perfect sense... and now I have two holes filled with broken taps. The only way I can think of getting them out would be to dissolve them with Nitric acid. Guess I'll just have to live with them in.

Anyway, the hard part is done, now it's time for the fun part! Next step is to solder the whole array together and build the pulse width modulator (LED dimmer box) which I should be able to get done by this weekend.

I'm aiming to set it up over the aquarium at some point next week, but that's also dependent on how I decide to hang this thing over the tank....

[gconcepcion]

I've been pretty busy lately and just so you guys don't think i've given up, here is a quick update:

Bad News: Soldered everything together and fried several LED's.

Good News: I learned many lessons about grounding, short circuits, measuring current, continuity, proper soldering technique etc. I will elaborate later

Where I am currently: Just ordered some replacement LED's, fried 6 of the original 12.... (Good thing JohnS recommended the paste & not the adhesive...)

I'm waiting for the new LED's to arrive before proceeding with the rest of the wiring. Right now i'm planning out the wooden frame to enclose the fixture.

As you might imagine, this weekend is going to be pretty busy so I probably won't get much further on this project until sometime mid - next week.

Hopefully next update will be a little more significant

[gconcepcion]

let there be light



Got the new LEDs in the mail today, was extra careful putting everything together, and was happy to be completely blinded with how bright it is.


Problems I ran in to and lessons learned:

1. I was so anxious to give the unit power that I didn't do a thorough check for grounding to the heatsink in all of the connections, resulting in several "pops" which i'm pretty sure were the diodes frying, although on visual inspection they appear to be in good condition. Lesson learned: Check for grounding with a a multimeter by touching one probe to the heatsink, while using the other probe to go around and touch all of the electrical connections in the array.

2. Wire gauge - I tried to solder the array together using 12 AWG monocore wire. Lesson learned: 12 AWG is WAY too big. The biggest problem it created was needing to use way too much solder, which created alot of the grounding problems I had. Switched to 22 AWG monocore and used minimal solder, no problems with grounding at all.




Things left to do:

- Build the PWM dimming circuit (just need to stop by radioshack to get some capacitors)
- Drill holes for mounting hardware
- Build a simple wooden frame enclosure

I might start testing it on the tank later this week, but I'll probably want to build the hood first and not rush it. (Last time I rushed it I made a $40 mistake.)

[gconcepcion]

Sorry for the lack of updates, this project hasn't been scrapped, but real life has gotten in the way. Between working 80 hours a week and dealing w/ other home BS, this has just been pretty low on my radar.

What's happened in the past month:

I cut, stained and sealed the hood that will fit around the heatsink, here's what it looked like pre- staining & polyurethane sealing:



What's left to do:
- Attach heatsink to hood
- Figure out why my pulse width modulator isn't dimming the LEDs like it should.

Hopefully this will get completed sometime soon.... My work desk is tired of having an unfinished LED unit sitting on it....

[bussardnr]

Has anyone else done this yet?

[sns26]

I'm in the midst of a tank build that includes a 27-led array based on Cree LEDs from Rapid LED. I used a large (32" long x 10" wide) aluminum heatsink, drilled and tapped, and two Meanwell drivers. Wiring and soldering was pretty easy, but I've also done a fair bit of such things before. I haven't yet hung the light above the tank, but will post pictures once I get there (maybe this weekend).

--sam

[eleontie]

I have a couple of questions to satisfy my curiosity, maybe the answer is trivial :
A. are the high output LEDs driven by AC or DC.
B. If driven by DC ( like any regular led) do they flicker just like the incandescent and flourescent lights or do they output constant light ?
C. the lights that we use currently are tuned to the human vision so we do not notice the flicker, what is the frequency that plants like ? do we just assume it is the same frequency we like ?

Eugen

[takadi]

Wow...okay, so I attempted to read through this thread and I think I'll save LED electrical engineering for another day...next year

[sns26]

My fixture is essentially done at long last. I switched out some of the blue LEDs that folks saw at the April meeting. I also turned up the current to just under max capacity for the LEDs to see what the top end lighting capabilities are. Well, at high power, this looks like a good way to boil water, not grow plants. Good thing I can dim it to whatever I like.

The overall specs are:

2 dimmable Meanwell drivers running:
10 cool white Cree XP-Gs
8 warm white Cree XP-Gs
and 9 neutral whte Cree XP-Gs.

One string is cool whites and neutrals, the other is warm whites and neutrals.