40 gal breeder 36" high light LED Project - Page 3 - The Planted Tank Forum
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post #31 of 72 (permalink) Old 06-03-2012, 04:35 PM
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I was lazy and went with some manufactured LED strips from vertex. worth the money? YES. with no other changes made to the house, my power bill has come down nearly $30 a month, plus no more freaking bulbs to change!





the tank is 2 weeks old now and will soon be ready for the first round of stocking

good luck on your build!
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post #32 of 72 (permalink) Old 06-04-2012, 02:40 PM Thread Starter
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Quote:
Originally Posted by Hoppy View Post
I'm disappointed in your professor. He missed a lot with his advice. Aluminum is actually a poor heatsink material. A heatsink needs to have a high specific heat, a high density, and high conductivity. Aluminum has a low density, making it relatively ineffective as a heatsink. Copper or Silver or Beryllium are much better heatsinks. But, LED lights don't use a "heatsink" as a heatsink. They use aluminum to conduct the heat from the LEDs away from the LEDs and dissipate it to the atmosphere. For that to work well with a high heat input the aluminum needs lots of surface area exposed to the air, thus, the fins. Without the fins, even thick aluminum bars will not work for LEDs running at high currents.
Really? Dr. Chen made a quick MathCAD file showing the difference between the flat bar and a fin model using 5 fins on top. I agree that a fin heat sink works a lot better but it doesn't justify the price and the file showed the flat bar performed reasonably well (we assumed led would get as hot as 343°K and only passive air currents using 6063 alloy). The desired heat sinks will only cost $21 for both of them, compared to $70 for two finned heat sinks from rapidled.com (not including the extra cost in shipping)
http://www.rapidled.com/1-4-x-36-aluminum-heatsink/

I would disagree, aluminum is a great heat sink. It is used in the cooling of many electronics and is even inserted in stainless steel pots because it has great heat transfer properties. Even a quick search in wiki and in my heat transfer book confirm this

" The most common heat sink materials are aluminium alloys.[5] Aluminium alloy 1050A has one of the higher thermal conductivity values at 229 W/m•K [6] but is mechanically soft. Aluminium alloys 6061 and 6063 are commonly used, with thermal conductivity values of 166 and 201 W/m•K, respectively. The values depend on the temper of the alloy.Copper has around twice the conductivity of aluminium and faster heat dissipation, but is three times as dense [5] and, depending on the market, around four to six times more expensive than aluminium. [5] Aluminium can be extruded, but copper can not. Copper heat sinks are machined and skived."
http://en.wikipedia.org/wiki/Heat_sink

I'm planning on using 6063 alloy which has a great density and heat transfer properties.
I agree that using copper or silver heat sinks would keep the leds at lower temperatures but the cost would be a lot higher.
A search for the same dimension of a copper bar costs $117.94, even more than the leds themselves.
http://www.amazon.com/Copper-Rectang.../dp/B000HZX44M

Using a heavier heat sink would only increase the price and make hanging the fixture more difficult. I bough 1/16" aluminum twisted wire capable of holding 120lbs. Which should be enough to hold the entire fixture. Using a heavier metal would make hanging the fixture more difficult since I'd have to reinforce the ceiling connection.


And regardless of materials a heat sink is a heat sink

Quote:
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The [leds] use aluminum to conduct the heat from the LEDs away from the LEDs and dissipate it to the atmosphere
And the definition of a heat sink is
" A heat sink is an object that transfers thermal energy from a higher temperature to a lower temperature fluid medium."
http://en.wikipedia.org/wiki/Heat_sink
Therefore a rectangular bar of aluminum made of 6063 aluminum with dimensions 1/4"x 2-1/2" x36" and leds attached on one side and passive air currents on the other side is defined as a heat sink.

I'm pretty sure the leds will get hot running at 1750 mah, and using a rectangular bar of aluminum 1/4" should help to diffuse the heat evenly, even if I feel the fixture is warming up too much then I can easily attach a $10 computer fan on one end and help disperse the heat, this should still be cheaper than getting a fin bar or a copper heat sink.


I definitely I appreciate your post hoppy, it really made me search more in depth into the heat sink issue. I think you're the guru of led fixtures and its always nice when someone points out a problem in the design process. :-)

--Oscar.
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post #33 of 72 (permalink) Old 06-04-2012, 04:32 PM
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I love to debate!! Your definition of a heat sink is a definition of a heat conductor, an entirely different function. A heat sink is a something that absorbs and stores heat. A heat conductor just transfers heat. Electronic "heat sinks" aren't heat sinks, but devices to transfer heat - heat conductors. Heat conductors need high conductivity alone, but heat sinks need high conductivity, and high heat storage capacity ( specific heat and density ). Aluminum is a great heat conductor, and when you provide a means of removing the heat from the aluminum, like fins and moving air, or water, it is a good way to cool something.

Do an experiment. Heat up a piece of aluminum foil, then touch it. It doesn't burn you because it doesn't hold enough calories of heat to raise your skin temperature. Do that with copper foil and you get burned.

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post #34 of 72 (permalink) Old 06-04-2012, 04:39 PM Thread Starter
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Oh I agree with you on that one hoppy
we studied heat sinks in thermodynamics. a large body of water, molten salt, those are all heat sinks( something that can store heat). but I think in real world application and in the electronics field then a heat sink is just a medium to transfer heat to a fluid, a basic heat conductor.

I'm hoping that the 2-1/2" wide bar will be enough to cool the leds, even with passive air cooling.
I just looked at the specification sheet and it said the Peak/Classification Temperature (Tp) is 215 įC.

I'll drop by Dr. chens office and see what he thinks.

Quote:
Originally Posted by Algae Beater View Post
I was lazy and went with some manufactured LED strips from vertex. worth the money? YES. with no other changes made to the house, my power bill has come down nearly $30 a month, plus no more freaking bulbs to change!

the tank is 2 weeks old now and will soon be ready for the first round of stocking

good luck on your build!
omg Algae Beater did you really spend $349.99 on each fixture??

--Oscar.
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post #35 of 72 (permalink) Old 06-12-2012, 03:17 PM Thread Starter
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eeek

FINALLY rapidled.com got some of the XMLs! I've been waiting for a while but the wait paid off (saving nearly $25)

I made my order of all the leds, optics, pads, heatsinks and hanging supplies.

I'll swing by the aluminum shop and pick up the heat sinks this week and i'll try building the fixture this weekend. then hopefully the supplies will come in next week and i'll get the fixture hung and take pictures of everything soon!

I'm very excited!!

--Oscar.
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post #36 of 72 (permalink) Old 06-17-2012, 02:11 AM Thread Starter
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wow, that was fast shipping.

all the supplies came in on Friday. I have 99% of the things needed to build the fixture. michael is coming over tomorrow to help me out. i'll post picture when everything is settled.

--Oscar.
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post #37 of 72 (permalink) Old 06-17-2012, 11:27 PM Thread Starter
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Got all everything soldered on and tested and it looks super bright. all the plants are pearling!

i'll post pics/vids and steps of the whole building process tomorrow after my exam

--Oscar.
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post #38 of 72 (permalink) Old 06-18-2012, 05:23 PM
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Nice! Looking forward to pics...

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post #39 of 72 (permalink) Old 06-19-2012, 04:49 AM Thread Starter
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As I was hanging the fixture from the ceiling and making sure it was leveled one of the heat sinks falls in and the leds get all wet. :-\

Everything was turned off and I dried what I could. I'm going to let them dry for a whole day and I'll try taking pictures tomorrow.... if it turns on

How disappointing, got everything built and perfect only to have it fall inside the tank at the last minute. Ugghhh

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post #40 of 72 (permalink) Old 06-22-2012, 06:28 AM
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Any updates? Dieing to see pics of the build process to sway me one way or another. Build my own or use T5HOs on my new 12g long
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post #41 of 72 (permalink) Old 06-22-2012, 06:47 AM
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Quote:
Originally Posted by monkeyruler90 View Post
How disappointing, got everything built and perfect only to have it fall inside the tank at the last minute. Ugghhh

Don't feel so bad. Thanks for sharing. Your experience including this set back will help many others. I will now definitely take additional precaution when it's time to hang the fixture!
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post #42 of 72 (permalink) Old 06-22-2012, 01:37 PM
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I hope you don't think that gets you out of posting pictures. Weather it works or not, WE WANT PICTURES!!!!!!!!!!!!!!!
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post #43 of 72 (permalink) Old 06-22-2012, 04:44 PM Thread Starter
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Yep pictures and a full description of the build are coming! Just started a new job this week that's why it was perfect timing that I had all the supplies last week or else I would have had to wait another week to build it.

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post #44 of 72 (permalink) Old 06-22-2012, 10:53 PM
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Woohoo!!
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post #45 of 72 (permalink) Old 06-23-2012, 02:56 AM Thread Starter
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LED Fixture background

Alright guys, sorry about the long wait. I started working at a new job on Monday so I've been a bit busy. But I'm so happy I got everything built last week

So I'm an engineer and I really like planning everything, I did the cost analysis of doing 8, 10, 12 or 14 led bulbs. Either XML, XPG, bridgelux, even the cheap china bulbs. I was trying to get the most amount of light for the cheapest price. I did most of the calculations on this Google spreadsheet.

I learned a lot during my research. I had just taken Principles of Electric engineering, thermodynamics, and programming so I knew the basics of wiring circuits, programming arduinos and a little bit about heat transfer. So this summer I decided to jump on the wagon and build the fixture. A big thanks goes out to Samamorgan for the Led lighting Compendium he created. Hoppy for the excel sheet he created to calculate the PAR at the bottom of the tank. Schneeball,dbosman@msu.edu, Algae Beater, and Raidendex or Michael for all the info they gave me on their own LED fixtures.

Since Raidendex lives nearby I kind of used him as a guinea pig for building an LED fixture over his 120 first. I used his mistakes to improve my design.


The first thing that was really important to me was the efficiency. At the time I was using 4 55w compact fluorescent bulbs over the 40 gallon and had them arranged perpendicular to the front glass. It did a good job of growing everything but it would be awkward when only two of the bulbs were running. Either half the tank was in shadows or the whole tank was fully lit. When I ran all 4 bulbs over the tank I would always end up with algae. Since buying 4 new bulbs every year would have added up and the fact that they weren't lighting everything evenly just pushed me more to try the LEDs.

The second thing was that I wanted it to be bright! I'm trying to grow plants like L. Pantanal and erios and I already had the CO2 and fertilizers. I really liked the t5ho fixtures for the 36" but the price of buying the fixture, bulbs, and energy cost would have been too high over the lifetime of the fixture.
I used two major websites to help me out. ledgroupbuy and rapidled , they had little FAQs and guides that were very helpful. The Cree website itself had all the specs of the bulbs and I used a lot of those to calculate the average light output. I really wanted to keep the fixture simple so I set up a circuit with the leds in series. The driver selection was a bit difficult but once I understood the forward voltage*current*number of leds= watts needed from the driver it all came together. I didnít care too much about dimming the LEDs, my dream tank is a 120 gallon tank so when I get that Iíll invest in a dimmable driver. If everything was too bright then I would just raise the fixture.
Using the spreadsheet I realized that the cost would significantly increase going from 10 leds to 12 leds since I would need to use multiple drivers. Keeping it low cost and simple I chose the 10 led set up. Roughly it would have given me 81 PAR at 20 inches which put me in the high light range. 12 leds would have given me 113 PAR but I didnít want to spend the extra $50 and turn the tank into algae heaven.
Rapidled had the cheapest prices around but they ran out of XML U2 lamps a while back so I had to wait nearly a month before they finally got some in stock. I would have ordered from ledgroupbuy but their shipping was a bit higher and the extra cost would have added up to $20 more than rapidled.
Once they finally got some bulbs in I placed my order coming to $128.90 , ordered the 40 degree optics from ledgroupbuy for $31.95 and then ordered my heat sinks which I was able to pick up locally for only $21.57 I went out to home depot and got 8í of primed linear 2-1/2Ēx1Ē, 13í of thin aluminum wire, 2 hooks, 2 sets of wire graspers and 1 snickers bar (most important part of the build) for $12.66.
Together I spent about $177.02 on the actual materials. On the side I spent about $100 extra getting a multimeter, 60 W soldering iron and a dremel tool kit which I used to build, test and assemble the fixture. I didnít count that in the cost since I needed that stuff anyway for other DIY projects.

Sorry, itís so long, just wanted to give a bit of background info. Iíll post the build pictures on the next post.

--Oscar.
Fluval pimp #4 aka PIMP master!
I SAID ITS GREAT
TO BE

A FLORIDA GATOR!!

40 gallon LED fixture
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