75 Gallon LED Hood

[phalanx]

I was wondering if you could glue the stars to the heat sink or do you have to mount them? Interested in building my own but all that drilling looks intense.

It is possible to get thermal adhesives for mounting the stars in lieu of the drilling and tapping method but as was mentioned by some other forum members, it makes the replacement of faulty LEDs much more difficult. You would also have to pay much closer attention to your surface preparation to ensure that the bond doesn't fail which could result in an LED overheating and failing.

TIM (thermal interface material) relies on surface prep as well since it needs to bond to both the star and the heatsink. You also have to have it die cut so it will fit your application. Some of the newer types have thermal properties almost as good as thermal paste and epoxies.

 

[phalanx]

Similar question - do you use any kind of heat conductive substance in between the LED and heatsink? Is there a heat conductive adhesive that would work?

In this application, we will have some kind of thermal compound (likely Arctic Silver or equivalent) between the sink and the star. There are a number of thermal adhesives that would work very well but they make future serviceability an issue.

 

[JayM]

thermal paste/glue should never get into the tank but id think its pretty toxic although if any gets in it will be a tiny tiny amount.

ive used thermal tape (pm me), two part epoxy, drilling and tapping and i can say that drilling and tapping is a major pain but is cheapest and most effective but it does give the risk of shorting the driver to the heatsink if you are slopping with the solder. ive never had the tape or epoxy pop off, the trick i guess is to clean the heatsink and star and apply strong pressure when the adhesive is attaching.

so, are you relying on the drill/tap for contact to the heatsink, or are you using the tape or TIM for this fixture? Also, how are the optics going to be attached?

 

[DoctaQ]

drilling and tapping allows you to press the star on to the heatsink very firmly, and a dab of heat conductive paste like arctic silver will help the heat transfer even more, its kinda like heatsinking a processor. it is also the least permanent, if you use glues or pads removing them will be more difficult and you will also need to get a new pad.

 

[JayM]

I don't mean to hijack, or be a pest, but are you sealing the LED's with the product mentioned above, since the conductive paste is considered reef toxic?

 

[DoctaQ]

the paste will not get into the tank unless you are talking about somehow water or saltcreep falling back into the tank, in which case you are also worrying about aluminum which can be bad as well but the fixture would likeley be in bad shape anyways.

bill, if you end up using that spray id be interested in the results, i was thinking of fitting up my bathroom with led and that sounds like it would be key

 

[number1gsxxr]

I forget if it was on here or Nano-Reef forum but I had asked about thermal interface material (TIM) and Bill (Phalanx) said it was unnecessary. I've always used it when assembling computers for the CPU heatsinks but I'm sure he'll chime in when he gets a chance. He travels a lot for work.

EDIT: I plan to have some layer of acrylic under the LEDs to protect from salt creep and water splashes.

My bad, I totally forgot that he said polishing the heatsink wasn't necessary. For some reason I had it confused with thermal paste.

 

[gajopo]

Where did you get the heatsink?

 

[number1gsxxr]

Where did you get the heatsink?

http://www.heatsinkusa.com/

 

[phalanx]

My day job has kept me on the road almost constantly for the past 2 months so I haven't had much time to work on the hood. Tonight I was able to get all 100 LEDs mounted to the heat sinks. Next up is the arduous task of soldering everything.

 

[DoctaQ]

score..do you figure youre going to need fans that heatsink seems pretty beast

 

[phalanx]

The sinks are large enough to be used without a fan at full power so long as it isn't mounted in a confined space. Odds are this will not be run at full power (likely 50% or less) which will greatly improve the thermal performance.

If for some reason this is boxed into a confined space with no room for convection, a quiet low velocity fan pulling air across it is all that should be needed.

 

[Flame Angel]

How is this project coming along? Any dollar figures yet?

 

[number1gsxxr]

Page 1 of the thread has some dollar figures but here is an updated list.

All costs include shipping.
$216 on the heatsinks.
$510 on the LEDs and mounting stars.
$14 on Arctic Silver Ceramique Thermal Paste. (2) 22-gram syringes (One syringe is more than enough).
$65 on mounting hardware. (150 aluminum pan head screws & nylon washers) Minimum package was 50 so I had a lot of extras.

$805 running total so far.

I still need to purchase the lenses, which should be around $100, and build the hood to hang the heatsinks. I won't include the hood in the cost as most people already have one on their tanks. My goal was around $800 but realistically even a $1000 is still way cheaper than anything commercially available.

 

[dcforester1]

Page 1 of the thread has some dollar figures but here is an updated list.

All costs include shipping.
$216 on the heatsinks.
$510 on the LEDs and mounting stars.
$14 on Arctic Silver Ceramique Thermal Paste. (2) 22-gram syringes (One syringe is more than enough).
$65 on mounting hardware. (150 aluminum pan head screws & nylon washers) Minimum package was 50 so I had a lot of extras.

$805 running total so far.

I still need to purchase the lenses, which should be around $100, and build the hood to hang the heatsinks. I won't include the hood in the cost as most people already have one on their tanks. My goal was around $800 but realistically even a $1000 is still way cheaper than anything commercially available.

What about the drivers? what type, and how many do you have to use. The light is coming out really nice.

 

[aiaman]

Sorry if I am late in the discussion but where did you find out about requirements for the spacing between LED's?
How many to use to provide for possible PAR you are trying to assimilate?
light deflection over a depth of water?
I'd like to find out a little more but I can't seem to find any information on what fixture would be the best for my particular tank or any tank for that matter.
Can you direct me?

 

[DoctaQ]

the driver is a custom driver that bill made
the number of leds and spacing is just to prevent spotlighting blues and whites, optics and drive current dictate the amount of light getting through

 

[phalanx]

Sorry for the long span between updates. My real world work has kept me very busy but this holiday season has given me a lot of time to catch up. I have finished the constant current drivers and finished soldering the full array. I was able to get full PWM dimming to function as well as a selectable high/low current range for a highly increased dimming range. There are 2 boards each with 2 channels which are easily driving 25 LEDs in series a piece. All 4 channels and high/low selection can be controlled separately to allow for any kind of mixing you would like. The interface is optoisolated so there is no risk of exposing yourself to dangerous voltages while the controller is running.

Constant Current Controller Specs (per channel):
Based around the Supertex HV9961: http://www.supertex.com/Feature_HV9961.html
120VAC input (fused)
Designed output of 90VDC @ 750mA
Fused output stage to protect the LEDs. Controller IC also supports a hiccup mode.
High current mode = 0-750mA
Low current mode = 0-150mA

Here is a video of the full array going through a multiple stage dimming cycle. My camera has a hard time capturing the intensity of the LEDs but needless to say, they are very bright and my workspace isn't as neat as it could be!

[video=youtube;otk_DJXooaA]http://www.youtube.com/watch?v=otk_DJXooaA[/video]

Here is a picture of the constant current controllers. I put a Comcast remote in the picture so you can get an idea of the size. Since these were prototypes, I made them on perfboard but I could likely make them a fair amount smaller if I layed out a proper circuit board. Those 2 boards controll all 100 LEDs.

 

[phalanx]

score..do you figure youre going to need fans that heatsink seems pretty beast

I ran the full array at maximum intensity for an hour with the heatsink upside down and it got warm but not hot. It should have no problems running without a fan.

 

[number1gsxxr]

That looks awesome. I can only imagine how bright that is in person. Tomorrow I'll get the sample optics in the mail to you.