Heatsink/shade for 7W led emitter - Page 1
Forum section: electronics / projects

author: ben7
author_rank: Contributor
timestamp: August 01, 2013, 04:00:25 pm
content: Hey everyone, my first thread hereSo, I have this project, which involves making three LED lamps for a kitchen. They are hanging style lamps. My plan is to use a 7W LED made by CREE, and make a metal enclosure/heatsink/lamp-shade for it.My idea was to have a cube made with aluminium plates around 1/4 an inch thick on 5 sides. The bottom side of the cube would have a frosted glass/plastic, as a diffuser. There will be a slot around it so air can flow in. And the top plate, the one that the led is mounted on, will have holes drilled into it. The idea here is for the warm air to rise and bring in cooler air, flowing through the metal fixture which also acts as a heatsink.The size of the fixure I want is around 7x7x4 inches (l,w,h).My question is this: do you think this design will be adequate for cooling the LED?This to be used inside, so the ambient temp is around 76 degrees F.Thanks,-Ben

author: Corporate666
author_rank: Unknown
timestamp: August 01, 2013, 07:46:53 pm
content: If you have a good thermal connection from the LED die to the outside of the case, then I think a 7" x 7" x 4" cube will be sufficient to cool the LED, assuming the LED is reasonably efficient. I am guessing you are talking about the MK-R LED's? I use those in some products and I have a significantly smaller heat sink than you and they run within reasonable specs.But it depends on how well you are getting the heat to that surface. The temperature falls off pretty quickly with distance through aluminum (drastic oversimplification, I know) so if your LED is on a copper MCPCB attached to the outside surface, that's very good. If it is attached to a 1" wide aluminum strip 1/8" thick that is attached at each end to the outside housing, that's not so good.

author: ben7
author_rank: Contributor
timestamp: August 02, 2013, 12:09:08 pm
content: I'm thinking of 1/4 inch thick aluminumHowever, I think can do 3/8 too. 1 inch thickness is available, but that seems like overkill xDI'm thinking of using these:http://www.mouser.com/ProductDetail/Cree-Inc/CXA1507-0000-000N00F440F/?qs=sGAEpiMZZMu4Prknbu83y8%252bOyfcV9kMehkLDDSW47XU%3d

author: SeanB
author_rank: Super Contributor
timestamp: August 03, 2013, 05:37:10 am
content: Just use the 3/8 on the LED mounting surface, and 1/4 or thinner as sides. Cut some slots on the 4 faces of the top, about 1/2in wide with about 1/4in spacing, to a depth of about 1/3 of the plate dimensions, keeping a solid area around the heat spreader on the LED and allowing a space for the mounting screws to be tapped in to the plate. That will allow heat transfer from the die to be dissipated by the plate. At the back you will need to have a small plate to mount the hanging cord so you do not have to drill through the plate by the LED, the leadout wires can simply be threaded through the existing slots. Just recess the mounting plate so the wire and mount is not visible, about 1.5 inch will probably do.

author: ben7
author_rank: Contributor
timestamp: August 03, 2013, 01:56:51 pm
content: Quote from: SeanB on August 03, 2013, 05:37:10 amWow great reply.I was just thinking of doing a whole series or holes on the LED plate. That way convection will help too.What do you think of that? Depending on how small (in diameter) the holes are, I would have extra surface area on the 'heatsink' too!And of course, I can always get heatsinks of any size from ebay, if I find a proper heatsink is needed.The driver will be on the fixture too, it is just a little buck converter that I am going to make. I plan on having a 48v unregulated power supply, and there will be about 10v to 20v to be dropped by the buck converter. As a bonus there is some headroom for wire losses. I really don't want those cheap chinese LED mains drivers, I don't trust them to keep the proper amount of current flowing through the LED!...