evilc66 Posted December 6, 2009 Share Posted December 6, 2009 I wouldn't do it. You will kill the thermal efficiency. It's not like you would be thermally connecting the two, so your surface area exposed to moving air is severely reduced. Link to comment
plantarms Posted December 6, 2009 Author Share Posted December 6, 2009 I wouldn't do it. You will kill the thermal efficiency. It's not like you would be thermally connecting the two, so your surface area exposed to moving air is severely reduced. will the 8 led's even make the heatsink hot enough for that to really matter? Evil would know more than I about whether there'd be enough airflow, but if so, how were you planning to mount the heatsinks to each other? From what I can see they just slide together, nothing really keeping them there right now except the weight of the top one. the heatsinks connect to each other and wedge in together, then i would put a screw in between the fins on each to push the fins against each other Link to comment
evilc66 Posted December 7, 2009 Share Posted December 7, 2009 Yes, it will get hot enough to matter. I wouldn't have mentioned it otherwise. Link to comment
Weetabix7 Posted December 7, 2009 Share Posted December 7, 2009 I have 7 LED's on the fixture I just got, and my heatsink doesn't even get warm. It stays room temp. Is it a mutant? Link to comment
plantarms Posted December 7, 2009 Author Share Posted December 7, 2009 Yes, it will get hot enough to matter. I wouldn't have mentioned it otherwise. alright then how would you reccommend mounting the heatsink? I have 7 LED's on the fixture I just got, and my heatsink doesn't even get warm.It stays room temp. Is it a mutant? what size is your heatsink? do you run the led's at full power? Link to comment
Weetabix7 Posted December 7, 2009 Share Posted December 7, 2009 Heatsink is 6 1/4" by 3 3/4". I've only had it for 2 days now, but yesterday I ran the Blues @ 75% and the Whites @ 50%. I do have fans wired up to it, maybe they're just removing any heat before I have a chance to feel it. I swear it always feels like it's room temp though. I should also state that I'm an LED noob and I didn't build this fixture, cptbjorn did. To my nooblet eyes, it looks like he did a really amazing job though. I posted a couple of pics yesterday on my "Weetie's Aquatic Ramblings" thread, but I need to get more detailed pics and info up today, if I can manage it. Link to comment
plantarms Posted December 7, 2009 Author Share Posted December 7, 2009 well you do have a fan running that helps remove the hot air that comes off of the heatsink and rises out through the fins, my problem would be that the top of the heatsink would not be open and allow air to come in and remove the hot air, which i'm hoping i could solve by having to fans in the fixture. i think i will build it with two heatsinks the way i have it and mount the led's and run them for a while with the fans to determine if there is an overheating problem. if there is then i will have to find a different way to mount it Link to comment
evilc66 Posted December 7, 2009 Share Posted December 7, 2009 alright then how would you reccommend mounting the heatsink? Take advantage of the features on the heatsink. The two slots on the sides of the heatsink, near the base, should be about the right size for a self tapping screw. Maybe a #4. Failing that, the sides should be large enough to drill and tap. Make a thin sheetmetal bracket that allows you to screw everything down to the mounting rails on the inside of the Satellite housing. Link to comment
plantarms Posted December 7, 2009 Author Share Posted December 7, 2009 thanks, i will look into that Link to comment
cptbjorn Posted December 7, 2009 Share Posted December 7, 2009 Weetabix if you crank up the LEDs to 100% and take the fans off the heatsink it will get hot enough that you can't keep your hand on it, it barely takes any airflow to keep it cool to the touch but it does need some unless the heatsinks are very large. With no airflow the air forms an insulating "skin" around the surface of the heatsink similar to if you stand near a wall or lay down on the ground on a windy day and it doesn't take much to break that skin. I mounted the heatsink in my satellite retrofit by tapping four #6 holes in the stock mounting brackets and then using standoffs (basically a tube with a hole just large enough to pass the screw) between the fins and through the face of the heatsink. Link to comment
evilc66 Posted December 7, 2009 Share Posted December 7, 2009 This is true, only if there is enough space between the fins to properly transfer heat to the air. Reducing the flow are (and creating dead spots) like plantarms wants to do will require considerably more airflow. A single 50mm fan will work fine with one heatsink all by itself. Link to comment
plantarms Posted December 7, 2009 Author Share Posted December 7, 2009 i do understand that having the heatsinks together like this will make the hot air that accumulates in the fins get trapped in between the two heatsinks as so it is probably not the best idea, however there will be a 40mm fan on one end blowing air, and a 40mm fan on the other end pulling air through the fins of the two heatsinks. would the greater amount of airflow not offset the heat accumulation? Link to comment
evilc66 Posted December 8, 2009 Share Posted December 8, 2009 No, because you aren't moving twice the air with twice the fans. A push-pull setup only moves the amount of air that one fan is rated for. If you had two in, that would be a different story, but where would it exhaust? Link to comment
plantarms Posted December 8, 2009 Author Share Posted December 8, 2009 No, because you aren't moving twice the air with twice the fans. A push-pull setup only moves the amount of air that one fan is rated for. If you had two in, that would be a different story, but where would it exhaust? it would exhaust on the other side of the heatsink. adding the other heatsink on top only creates a cover and makes the fins a little thicker. when i blow a small breath, i can feel with my hand the air exit the other side of the heatsink. then the fan pulling the air out of the heatsink on that side would push it out through the side of the fixture vent. Link to comment
evilc66 Posted December 8, 2009 Share Posted December 8, 2009 Ok. Quick example. Take two fans that move 10cfm each. Put them into two theoretical fixtures. With both fans blowing into fixture, and exhausting through a vent, you move 20cfm. With one fan pushing air in, and one fan pulling air out, with no additional venting of the fixture, you are moving 10cfm. There is no arguing this. This is how it works. With the heatsinks stacked, you aren't actually adding any thickness to any fins. All you are doing is reducing the air contact area of the heatsink. The limited contact area when you cram the two heatsinks together is not enough to benefit the setup thermally. Honestly, you will be better off with only one heatsink, and will see lower LED temps, and have less noise from airflow restriction. Link to comment
plantarms Posted December 9, 2009 Author Share Posted December 9, 2009 just received fans in the mail today, still waiting on LED's and buckpucks Link to comment
plantarms Posted December 12, 2009 Author Share Posted December 12, 2009 also picked up some led mounts for the 5mm moonlights, received tapping tools today, and ordered an extra rocker switch to install to have a switch for the blue and white seperately. led's should be here early next week! Link to comment
evilc66 Posted December 12, 2009 Share Posted December 12, 2009 Good deal. Looking forward to the results. Figured out your heatsink mount yet? Link to comment
plantarms Posted December 12, 2009 Author Share Posted December 12, 2009 not yet, still weighing my options. i'm taking a lot of the features from your satellite mod and putting them into this fixture Link to comment
plantarms Posted December 14, 2009 Author Share Posted December 14, 2009 just received order from LED supply! tested the LED's and buckpucks and everything is working, i'm going to try to start drilling and tapping tonight Link to comment
Walking_Target Posted December 14, 2009 Share Posted December 14, 2009 If you have the patience, i'd suggest getting some 000 steel wool and going to town on that thing, give it a mirror shine Link to comment
plantarms Posted December 14, 2009 Author Share Posted December 14, 2009 If you have the patience, i'd suggest getting some 000 steel wool and going to town on that thing, give it a mirror shine i will have plenty of time over the break, maybe i will postpone the tapping and do that Link to comment
Walking_Target Posted December 15, 2009 Share Posted December 15, 2009 I do that with my Automag bodies (stainless steel paintball gun bodies). Takes forever and a day, but you can eventually get them to a mirror shine with just steel wool. Link to comment
plantarms Posted December 15, 2009 Author Share Posted December 15, 2009 I do that with my Automag bodies (stainless steel paintball gun bodies). Takes forever and a day, but you can eventually get them to a mirror shine with just steel wool. just work from 0 to 000 using a small circular motion with each one? i have heard people use sandpaper increasing to very fine grades to do this, which process works better? Link to comment
Walking_Target Posted December 15, 2009 Share Posted December 15, 2009 I personally like steel wool because you use it dry or with a very small amount of WD-40. Sandpapers (to get a mirror surface) need to be water paper... and that involves water... which is messy. With steel wool, when you get fine enough, it's burnishing which is not quite the same a sanding. Besides, with steel wool used dry, you can sit in front of the TV with a movie on, which helps with the boredom. Link to comment
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