DIY LEDs - The write-up

[der_wille_zur_macht]

That's wirewound. I've heard anecdotal evidence that wirewound are "bad" for precision use (i.e. as a current sense resistor) but I don't know the reasoning behind that. Any thoughts?

Also, I totally agree about getting a 1%. And a higher power rating. I just grabbed the first 1ohm 2w resistor I found.

 

[salcedo5]

Nice thread. What do you think about this driver? How many 3W LEDs can we use with it?
http://www.dealextreme.com/details.dx/sku.48280

 

[kcress]

Good point Willie... It could be a problem but a doubt it. It's now pretty hard to find non-wire wound resistors. Composition which were excellent and non-wirewound are now crazy hard to find and expensive, like north of 10 bucks often.

Resistors are now made by etching a wire spiral down the barrel. So they are the same they just don't declare them "wirewound".

I don't expect an issue at the frequencies these drivers are running at. Also while they can be inductive they are only air cored so the inductance is low.

 

[wfournier]

Nice thread. What do you think about this driver? How many 3W LEDs can we use with it?
http://www.dealextreme.com/details.dx/sku.48280

Based on the specs the voltage adjusts between 30 and 36v so it really depends on the forward voltage of the LEDs.

 

[DFason]

Cant sleep! Must finish!

I gladly accept donations for sunglasses.

-Dave

 

[kcress]

Looky at that!! He did it!

Do tell..

 

[Milad]

wth is that fixture lighting up? looks like Jesus' face.

 

[S2minute]

LEDs

LEDs

...That`s pretty wild DFason, congrats man! :celeb3:

 

[mseepman]

DFason, Looking good...so what was the fix? Dying to know as I'm going to be embarking on a big parallel build soon.

 

[katchupoy]

Stupid question. Do you use thermal adhesive to connect the optics? for some reason what i have doesnt snap in. you can just put it there but thats it, there is nothing holding it.

Thank you.

 

[kcress]

Negative. Use a tiny, TINY bit of two part epoxy. The tiny bit is so you can tear them back off without screwing things up if you want. Do not use superglue as that could fog the LEDs.

 

[DFason]

Thanks guys, I feel like a proud parent right now...

I have been slammed but here you go. I'll be back later to tell.

The Army!

Perfection

-Dave

 

[vthondaboi]

C channel question

I picked up some 3/4" C channel from HD that's 1/16" thick. How many inches per LED would be safe?

 

[katchupoy]

Negative. Use a tiny, TINY bit of two part epoxy. The tiny bit is so you can tear them back off without screwing things up if you want. Do not use superglue as that could fog the LEDs.

Thank you for fast response Kcress. I building mine right now, and I was just wondering how you do yours... Thank you.

 

[kcress]

vthondaboi; Usually it's not an asked question because other things dictate the spacing, like the width of the optics. Or the fact that you generally don't even want them spaced really close because you don't need that many LEDs to achieve the 15sqin/LED. You don't need them all directly next to each other. I'd say an inch or two, star edge to edge would be as close as you'd want.

 

[kcress]

katchupoy;

The optics alllllmost stay on by themselves usually. So you need a really small amount of epoxy to hold them so they'd never just fall back off. After fitting a few, just look for a convenient spot where the optics touch the star.

Use a toothpick and dab a tiny amount onto the optic and then re-install it. I have also seen the other method where you put on the optic and then just dab a bit of epoxy somewhere at the seam between the optics and the star. Just enough to make a tiny little bridge across the seam. Often you want to use 30 minute or 1 hour epoxy because you have longer to apply it before it goes off on you. Then just leave everything and come back the next day.

 

[wisewendell]

I am planning on building a fixture for my 48wx26tx24d 150 tank. Using 68 LEDs. 4 red, 4 green, 20 white and 40 blue. Using a 24V 10A driver with resistors and all that on a 16"X8" heatsink(square tube)that I will probably spread out a little to get around 10". Plan on using 24V PWMs to control the strength of each color. Will this be sufficient light to grow LPS and some SPS on? I plan on driving the bulbs not turning them down to 1/3rd power.

 

[kcress]

wisewendell; LEDs Man, L E D s not bulbs.

Have at it. You should use U channel though NOT tubing.

 

[kcress]

I got ahold of an XM-L. I fed 700mA to it and was suitably impressed. Make that VERY impressed.

Besides the crazy amount of light - 260 lumens - that it spewed, I was impressed by the fact that I could hold it in my fingers without it getting noticeably warm. This means that if you ran XM-Ls at 700mA you could use a really minimal heatsink scheme.

I did screw it to a small stamped heatsink and cranked it up to 2A. That was 650 lumens or about 1/2 a 100W light bulb!! That started to warm up the heatsink a bit.

I'd probably consider 1.5A to be a good working maximum for the XM-Ls. That would still allow fairly lean heatsinking without a concern-able lifetime impact.

I can't see using them without optics though. The wide dispersion of so much light will have a lot of light hitting places it shouldn't.

I dropped some optics on it that included 25, 20, 15, and 5 degrees. They all made a great spot on the ceiling 5 feet above.

Any of those spots would make a great bike light with only the one XM-L. I didn't have any proper optics though. These were for LumiLEDs. They are the plastic cones with a recessed hole that fits down over the LED. They result in just about zero leakage out the sides. Anyway using proper optics and mounting them above the tank a foot or two would be great. You could crank the factors up to maybe 20sqin/LED.

 

[Frode]

wow kcress, I posponed all my further plan with LEDs just to hear great news like this.
Can't wait to get my hands om some XM-L6