DIY LEDs - The write-up

[onetrickpony]

By evilc66

So, what has 36 LEDs, draws 194W, and can throw 1500 PAR at 18" with a crisp 12K color temperature?

:bounce3:

 

[widmer]

I like the idea of "cheaper" haha but haven't got many options for heatsinks in Canada.

I'm terrible at scrolling in the upward direction :lol: so I'm not sure if anyone's said this yet, but GET ALUMINUM U-CHANNEL from the hardware store. It comes in like 6-foot pieces of U-shaped, 1" wide aluminum that is like 1/8" thick and it's perfect for this application.

 

[widmer]

By evilc66

So, what has 36 LEDs, draws 194W, and can throw 1500 PAR at 18" with a crisp 12K color temperature?

Looks nice and professionally-built with that splash guard and all. Oh, and I love the racing stripes on the power supply :lol:. But I'm soooo skeptical of LEDs that aren't late model Crees, as one of the primary benefits of LED is its energy efficiency, which often just isn't there with basically every LED that is not late model Cree. Nevertheless, those four larger LEDs look interesting. So... can you find a spec sheet wherever that pic came from?

 

[mseepman]

I'm terrible at scrolling in the upward direction :lol: so I'm not sure if anyone's said this yet, but GET ALUMINUM U-CHANNEL from the hardware store. It comes in like 6-foot pieces of U-shaped, 1" wide aluminum that is like 1/8" thick and it's perfect for this application.

Are there not some long term concerns how the U-Channel will handle the heat. With heatsinks I planned on putting fans on top...but with U-Channel I'm not sure of how to cool the aluminum. Will I have to turn down the amperage of the LED's to maintain a decent temperature? I was planning to use one U-Channel for the moon-lights already but there are only 5 of them.

 

[wfournier]

By evilc66

So, what has 36 LEDs, draws 194W, and can throw 1500 PAR at 18" with a crisp 12K color temperature?

:bounce3:

Looks like some of the stuff I've been playing with :-D

<a href="http://www.flickr.com/photos/wfournier/5259484766/" title="IMG_0341 by wfournier, on Flickr"><img src="http://farm6.static.flickr.com/5248/5259484766_35ce3f60d8.jpg" width="500" height="375" alt="IMG_0341" /></a>

 

[kcress]

Are there not some long term concerns how the U-Channel will handle the heat. With heatsinks I planned on putting fans on top...but with U-Channel I'm not sure of how to cool the aluminum. Will I have to turn down the amperage of the LED's to maintain a decent temperature? I was planning to use one U-Channel for the moon-lights already but there are only 5 of them.

No long term problem. The key point is to make sure that adjacent U-channels are separated by at least a quarter inch.

U-channel competes very well with heat sinks because in the horizontal plane we have to build our fixtures in, the vertical heatsink fins perform the worst while the sides of U-channel are in the optimal orientation for convection cooling.

 

[MosMike]

I like the idea of "cheaper" haha but haven't got many options for heatsinks in Canada.

If I stick with heatsink USA...this got even more expensive

Call them: http://www.bonlalum.com/Login/SalesEng/SEStandardShapes.jsp

I think that U-channels can handle up to 500mA, but of course it will depend on the dimensions. Rule of thumb: 10 cm2 of heatsink surface per 1 W

 

[bamf25]

So what is the current color mix recomended using XP-G whites and XP-E RB's. I do not mind putting a few blues or even green in there to give it a little warmer rather than blue look. My current plan on a 72 x 18 125g tank is to run 72 leds, 29 cool white XP-G's, and 43 RB XP-E's. Thes would be in 3 linear strips. The center would be a mixed strip with 2 constant rate drivers and include 19 RB's and 5 whites. The other two rails would be dimmable with and even split RB to white, and individual color control. It would be this......


BWBWBWBWBWBWBWBWBWBWBWBW Dimmable
BBBBWBBBBWBBBBWBBBBWBBBBWBBB Constant
WBWBWBWBWBWBWBWBWBWBWBWB Dimmable

This is a 60/40 ratio. Guess i could try the nutral whites also.

 

[TheFishMan65]

60/40 is the recommended when mixing XP-G and XP-E, but it is all personal taste. I have not heard enough on adding blue or green, but I have heard positives on neutrals.

 

[der_wille_zur_macht]

Call them: http://www.bonlalum.com/Login/SalesEng/SEStandardShapes.jsp

I think that U-channels can handle up to 500mA,

I don't know if I'd make that sort of general restriction. I've run lots of LEDs on U-channel at typical spacings and power levels (i.e. an LED every 2 - 3", 700mA) with a fan and things are totally fine. Without a fan, yeah - I'd be really worried and would scale back. Clearly though there are lots of variables that are going to come in to play. But given the performance I've seen from home-built U-channel "heatsinks" I really have come to the conclusion that the heatsink-usa stuff is wildly overkill, expensive, and heavy.

 

[TheFishMan65]

MosMike,
"Rule of thumb: 10 cm2 of heatsink surface per 1 W". First time I remember hearing this. Could you please tell me more?

 

[The Grim Reefer]

I run 2x1 1/8th channel with the LED's inside the channel and temp isn't an issue. You can find the stuff online.

 

[katchupoy]

What about the moonlights...are these too powerful (even if I use only 5 XR-E's over a 7' tank?)

This is what I used. Runs directly on 12 volts, and can be dimmed (voltage selector) You can cut and solder it for max flexibility. And also sealed for protection with water splash or whatever.

http://www.autozone.com/autozone/ac.../_/N-25pt?counter=8&itemIdentifier=22380_0_0_

$20.00

 

[TheFishMan65]

I am apparently missing something.

The XP-G produce 139 lumens at 350 ma. At 700 ma it produce 180% as much or 250 lumens and runs at 3.2 volts so 250 / (3.2 * .7) = 111.6 lumens per watt.

The XM-L produce 280 (if you get the best) lumens at 700 ma. At 700 ma it runs at 2.9 volts so 280 / (2.9 * .7) = 137.9 lumens per watt.

I thought someone said they were twice as good or at least way better. If you look at lumens at base current it appears that way, but not if you do the math. So did I miss something or am I remembering wrong? they are 25 more efficient which is a good thing.

 

[widmer]

XM-L is approximately twice as efficient as XR-E, and approximately 20% more efficient than XP-G.

 

[TheFishMan65]

Oh that is where the 2x comes from. For those that care.

The XR-E produce 107 lumens at 350 ma. At 700 ma it produce 170% as much or 181.9 lumens and runs at 3.6 volts so 181.9 / (3.6 * .7) = 72.2 lumens per watt

 

[jpccusa]

But given the performance I've seen from home-built U-channel "heatsinks" I really have come to the conclusion that the heatsink-usa stuff is wildly overkill, expensive, and heavy.

I was thinking the same...

I never understood why add almost 25 lbs to my canopy to cool down something that 1) doesn't get too hot, 2) can be easily achieved by a $4 few ounces heavy fan(s).

Since I am not putting the LED's too close together, I'm actually planning on using any type of sturdy flat metal sheet (metal screen?) as my heat sink - cheap and available at Home Depot.

 

[TheFishMan65]

The disadvantage of fans is they cost money to run and can be noisy. Long term is it cheaper to get a heatsink or run a fan. I don't know.

IMHO do not use screen. You will not get good thermal transfer from the star. Now if you could only punch holes away from the start that may help. A large sheet will not have much flow in the center. Do you have a break? Maybe you could make your won U channel?

 

[wfournier]

I was thinking the same...

I never understood why add almost 25 lbs to my canopy to cool down something that 1) doesn't get too hot, 2) can be easily achieved by a $4 few ounces heavy fan(s).

Since I am not putting the LED's too close together, I'm actually planning on using any type of sturdy flat metal sheet (metal screen?) as my heat sink - cheap and available at Home Depot.

My experience is just the opposite, however I'm usually running them at 1A, I'd be very worried running them on U channel. I'm actually replacing a 8X8 heatsink USA heatsink with one that has twice as many fins that are an inch taller (and I'm using a fan).

 

[MosMike]

MosMike,
"Rule of thumb: 10 cm2 of heatsink surface per 1 W". First time I remember hearing this. Could you please tell me more?

This was from an old Cree document. They determined that a 1"x1" flat surface is sufficient for 1W LED without fans. I repeated the experiment - the LED was too hot, so a 1.25x1.25" surface is a safe margin.

Of course with active cooling U-channels are sufficient for 2-3W per LED, but I prefer passive cooling. Also we should not forget that hot LEDs are less efficient than cool. For example, @350mA with a die temp of 35C the loss is 3%, @700mA with a die temp of 75C the loss due to overheating is 12%. This means that such losses will be higher in an XM-L @>1000mA vs. XP-G of the same cost.