DIY LEDs - The write-up

[widmer]

bstohrer: It's not totally clear how far the LEDs will be spaced out? I think the aluminum should be fine provided you have adequate air flow and they are spaced far enough apart. IE a few pages back when I was questioning whether I should use a fan on my heatsinks, someone posted a data sheet for similar LEDs (luxeon?) which specified that no active cooling was necessary if each LED got its own 6x6 inch area on a flat 0.0625" aluminum plate.

Also I'm putting up my XRE-based fixture this weekend and IMO it should be the last one to ever be built that is XRE, due to the fact that XPGs are out and so much more energy (read: also heat) efficient than XREs and are pretty much the same price depending on where you go ie the nano reef forums group buy...

 

[bstohrer]

bstohrer: It's not totally clear how far the LEDs will be spaced out? I think the aluminum should be fine provided you have adequate air flow and they are spaced far enough apart. IE a few pages back when I was questioning whether I should use a fan on my heatsinks, someone posted a data sheet for similar LEDs (luxeon?) which specified that no active cooling was necessary if each LED got its own 6x6 inch area on a flat 0.0625" aluminum plate.

Also I'm putting up my XRE-based fixture this weekend and IMO it should be the last one to ever be built that is XRE, due to the fact that XPGs are out and so much more energy (read: also heat) efficient than XREs and are pretty much the same price depending on where you go ie the nano reef forums group buy...

Thanks Widmer,

I'll space the LEDs at 3" center to center. I will likely use 24 XPG CWs (40 or 60 degree optics) on the front 2 bars (12 per bar) and 24 XREs CWs (60, 80 and no optics) on the back 2 bars. I didn't want to use all XPGs because only 120 (no lens), 40 and 30 degree optics are available from the Nano Reef group buy. I can get 90 (no lens), 80, 60 and 40 for the XREs. I may rethink the XREs based on your comments. I'll use 48 XRE RB on all bars (12 per bar). Total LED count is 24 per bar.

Your right - XPGs: higher output + equal wattage = less heat per lumen

I'm also finishing up an 18 XRE fixture for my refugium this weekend. I'll see how cool it runs with and without fans.

 

[TheFishMan65]

Sorry Widmer

Sorry Widmer

I only answered the first question why a capacitor.

Your math is right, but your logic maybe wrong since I don't remember the specs. I thought the buck puck required a 2 volt overhead, but maybe not since you don't appear to have it anyway.

You need 22.2 volts to drive the leds. You only have 24. If the BUckPuck does not require 2 extra volts your fine.

In the same sense with the long leads (and 3 buckpucks) you will only have 23.89 volts. 1.8 overhead might be okay (or on the limit), but 1.69 may fail. Sorry to be wishy-washy, but I don't have the specs in front of me right now.

Also this only took into account resistance from the wire. A bad connection can easily have more resistance than the wire.

I honestly think you will be fine, but never used these I want to rry and give you as much information as I can. Especially since I didn't answer you the first time:lol:.

 

[der_wille_zur_macht]

I thought the buck puck required a 2 volt overhead,

By the datasheet's requirements it does, but:

1) Many, many people are running 6 XR-E at 700mA or 1000mA on a buckpuck on a "24v" supply without a problem, while by the math they'd be a few 1/10ths of a volt short.

2) The standard-issue 24v power supply from mpja has a voltage trimpot that covers a HUGE range - like, 20v - 28v. So if you did find that you were a fraction of a volt off, it could easily be trimmed up a bit to solve the problem.

Again, I'm no EE, but I doubt that static voltage drop was the reason the manufacturer was concerned about long leads. It would be interesting to put a buckpuck on long leads and look at the input and output on a scope.

 

[der_wille_zur_macht]

I'm also finishing up an 18 XRE fixture for my refugium this weekend. I'll see how cool it runs with and without fans.

What color LEDs? Is this to grow algae or frags?

 

[Skeptic_07]

I'm sitting here trying to determine how to space out my LEDs using trig. I want to raise my fixture up 12" off the tank and planned on using 40 dge optics but what I'm finding is that each LED will cast a huge light like 27" radius 33" down (tank is 21" high plus the 12" above water). Am i doing this right? When they say 40 degrees, they mean 40 deg off center, right? And so to find out the radius of the circle of light 33" down you do (tan 40) * 33 which equals about 27"! thats huge!

 

[TheFishMan65]

Sounds about right at 45 degrees they would be equal 33 inches so 66 total spread. And at 30 degrees 16.5 or a total of 33.

Oops: FWHM is the whole thing so I should not have doubled for both sides. So 45 degrees will spread 33 inches and 30 only 16.5 so 27 sounds about right for 40.

 

[der_wille_zur_macht]

Skeptic, look back three or four pages - we had some math about coverage. IIRC, the "average" build had 30 - 40" diameter per LED at an average point in the tank.

 

[Skeptic_07]

Thanks fishman. Considering that 27" is only a radius, and theres going to be a few rows of these, the fixture is going to be able to illuminate a >60" area, back to front, which seems ridiculous now.

 

[der_wille_zur_macht]

Seems crazy but it's typical. AND it's probably smaller than what you'd get for coverage from a "typical" T5 or MH build. At any rate, the coverage area an LED lights with an optic will not be even intensity from edge to edge, it'll be much more intense in the middle (in your tank).

 

[TheFishMan65]

Could someone who truly understands this respond. Originally though radius also, but after I looked at Wikipedia I started to wonder if it was diameter. Anyone got a good link out there?

thanks

 

[Skeptic_07]

you mean this DWZM? Thanks for reminding me about that chart. I was lit when I read that and completely forgot about it. thx fish man too this is making things easier.

Widmer you and der_wille_zur_macht were discussing this in the "underwater LED setup help" thread (http://www.reefcentral.com/forums/showthread.php?t=1774231&highlight=degree), I think.


Degree..... 6 ft ...... 5 ft ...... 4 ft ...... 3 ft ...... 2 ft ..... 1 ft
.. 6 ... 7.56750 ... 6.30625 ... 5.04500 ... 3.78375 ... 2.52250 .. 1.26125
.. 8 .. 10.11894 ... 8.43245 ... 6.74596 ... 5.05947 ... 3.37298 .. 1.68649
. 40 .. 60.41517 .. 50.34598 .. 40.27678 .. 30.20759 .. 20.13839 . 10.06920
. 60 . 124.70766 . 103.92305 .. 83.13844 .. 62.35383 .. 41.56922 . 20.78461
. 80 . 408.33229 . 340.27691 . 272.22153 . 204.16615 . 136.11076 . 68.05538


Disclaimer: Lenses are definitely not my specialty

 

[der_wille_zur_macht]

It's typically a FWHM measurement - full width, half maximum. It's the angle at which half the max. intensity occurs. So it's a diameter, not a "radius". But it's only to half the peak intensity, so it's really just a suggestion of where the intensity is, not a sharp cutoff.

 

[Skeptic_07]

Seems crazy but it's typical. AND it's probably smaller than what you'd get for coverage from a "typical" T5 or MH build. At any rate, the coverage area an LED lights with an optic will not be even intensity from edge to edge, it'll be much more intense in the middle (in your tank).

Makes me want to cram a bunch of LEDs as close together as possible. I mean you can see right on the chart, 12" below the lens will be a ~10 inch radius circle of light and since my tank is 18" back to front thats a bunch of light spill. O well..... I wonder if someone makes 30 degree optics. Seems like it would work better.

 

[Skeptic_07]

It's typically a FWHM measurement - full width, half maximum. It's the angle at which half the max. intensity occurs. So it's a diameter, not a "radius". But it's only to half the peak intensity, so it's really just a suggestion of where the intensity is, not a sharp cutoff.

oh so i was doing it wrong then. I should be doing (tan 20) * 33 ... doh thx again

 

[der_wille_zur_macht]

Makes me want to cram a bunch of LEDs as close together as possible. I mean you can see right on the chart, 12" below the lens will be a ~10 inch radius circle of light and since my tank is 18" back to front thats a bunch of light spill. O well..... I wonder if someone makes 30 degree optics. Seems like it would work better.

Trust me, you DON'T want to use optics tight enough to keep the entire circle inside the tank - you'll get a really splotchy appearance.

 

[bstohrer]

What color LEDs? Is this to grow algae or frags?

All cool whites for algae.

 

[TheFishMan65]

Any way I can edit an old post? The table is correct I think, but I said it needed be doubled, and that appears not to be true. Just trying to avoid confusing someone that doesn't read the whole thread - or forgets half of it in the time it takes to read it all:lol:

 

[der_wille_zur_macht]

All cool whites for algae.

Any reason you didn't go with warm white? It has a more "typical" spectrum for algae. Let us know either way how it works.

 

[der_wille_zur_macht]

Any way I can edit an old post? The table is correct I think, but I said it needed be doubled, and that appears not to be true. Just trying to avoid confusing someone that doesn't read the whole thread - or forgets half of it in the time it takes to read it all:lol:

PM a moderator and ask them - they can edit old posts, us mere users can't.