Heatsink for 50w led - Page 1
Forum section: electronics / beginners

author: asuran
author_rank: Newbie
timestamp: December 19, 2012, 07:14:10 pm
content: Hi I am planing to make one led lamp .I would like to use 50w led, and hausing will be from aluminum. One plate size 300x150x30 mm without ribs, whether this will be enough?How to calculate the thermal conductivity of this plat?Thanks

author: Razor512
author_rank: Regular Contributor
timestamp: December 19, 2012, 08:13:21 pm
content: Sorry for not being too helpful in advance.I would like to know, do they make 50 Watt LED's (a single LED that uses 50 Watts?)I am currently working on coming up with a good flashlight that will use a few 1000-1200 Lumen LED's and to keep them cool, I will use thermal epoxy to attach them to an old CPU heatsink (if it can handle a 90 watt CPU then it should be able to handle 10-15 watts of LED's)(just stuck on finding a low cost way to manage a Li-ion battery so that I am not over discharging it, and possibly sometime in the future, find a decent way to charge the battery rather than using the old phone as a charger for the battery)your planned heatsink has about 80% more surface area than my CPU heatsink that measures L: 60mm, W: 60mm, H: 32. But my heatsink takes up much less space since it uses fins to save space 9though it will be a little harder to for it to be passively cooled than a single flat plate.

author: ee851
author_rank: Regular Contributor
timestamp: December 19, 2012, 08:25:20 pm
content: I have put up to six high-power LEDs drawing around 0.75A on a CPU heatsink. No problem. Great idea.

author: asuran
author_rank: Newbie
timestamp: December 19, 2012, 08:30:29 pm
content: Yes they make one chip for now max power is 200w (one chip)50w chip need 1750 mA, 33V, and provide 5000 lm.About heat sink, your cpu heatsink have fan?

author: Psi
author_rank: Super Contributor
timestamp: December 19, 2012, 09:13:00 pm
content: They make high power 10-200W leds, but they are in-fact a series array of smaller leds in one package.You can tell because their voltage is so high and you can normally see the array on top.eghttp://dx.com/p/prime-100w-7000lm-led-emitter-metal-plate-warm-white-42807

author: ee851
author_rank: Regular Contributor
timestamp: December 19, 2012, 09:45:35 pm
content: No, the CPU heatsink doesn't have a fan. Only dissipates 6.3W. With 50W, though, you'll probably want to have a fan in a duct with thermostatic speed control--the hotter the LED gets, the faster the fan turns.

author: mazurov
author_rank: Frequent Contributor
timestamp: December 19, 2012, 10:12:47 pm
content: That's what I use for experiments. On the left, noname chinese 30W LED is mounted on Intel CPU heatsink. It works well and I have another one which handles 50W with not much difficulty. On the right, a 40W Cree CXA2011-0000-000P00J050H is mounted on another Intel CPU heatsink (this one is much older). It is barely adequate. Both need fans run at 12V to keep cool, without a fan they overheat rather quickly.

author: Alex
author_rank: Regular Contributor
timestamp: December 19, 2012, 10:36:39 pm
content: Hi asuran,Just to confirm, the heatsink in your original post is a solid block of aluminium with dimensions 30cm x 15cm x 3cm?Alex

author: asuran
author_rank: Newbie
timestamp: December 20, 2012, 01:31:02 pm
content: Hi Alex,Yes its solid block of aluminium in this dimension.thank you

author: Alex
author_rank: Regular Contributor
timestamp: December 20, 2012, 08:20:30 pm
content: Ok, have a look at this finite element simulation using the dimensions you provided. Please note that there have been a number of assumptions made to produce this. The LED is positioned at the middle top of the aluminium block.It is quite clear that the heatsink you originally proposed is more than sufficient. The temperature rise of the LED will be in the region of 10-20 degC.For a more practical application you could consider a smaller heatsink of more complex geometry (eg fins) and allow for a higher temperature rise. An old CPU heatsink is common and you are already looking into this.Alex

author: asuran
author_rank: Newbie
timestamp: December 20, 2012, 08:38:21 pm
content: Dear Alex,Thank you for help, can i know what software you use for that?Please check me few more thing if you have time:-can i use aluminum in dimesion 200x100x20 for 50w led ? I can make ribs on cnc if is needed?- can you give me minimum dimension of aluminum for led of 30w led, I am planing to use 150x150x20 will this be enough?Thank you

author: Alex
author_rank: Regular Contributor
timestamp: December 20, 2012, 09:25:35 pm
content: You are welcome.Certainly, I used Quickfield.For your other questions, I think you should approach the problem from a different angle. You see, even if an entire car was used as a heatsink for the LEDs, it would not be sufficient if you covered it with enough foam...I propose you use a heatsink that:Is made from aluminium or copper.Has a large surface area. This usually means having fins. If you are not using a fan, keep the fins widely spaced.Is painted or anodised black.In terms of positioning:Position the fins on the sides, perpendicular to the direction of gravity.Leave plenty of space below and above the heatsink.Place the entire assembly in a well ventilated area, i.e. not a closed box or cabinet.In terms of assembly:Clean the heatsink surface from oils, especially if you are machining your own. Also the LED surface. Polishing to a mirror-shine will improve thermal transfer further.Use a good quality thermal paste, as little as possible to form a thin film.Your mounting of the LED on the heatsink should be done with uniform force. Eg, use screws in all holes of the LED.These guidelines will be helpful to get good performance out of any heatsink. Now, how big or small should the heatsink be is hard to answer as there is no single ideal answer.Have fun experimenting with different heatsinks while keeping an eye on the temperature rise of the LED die itself (higher than the LED package). If you would like to make your own, a shape like:http://preview.tinyurl.com/cservjxwould work very well.Good luck!Alex.

author: sorin
author_rank: Frequent Contributor
timestamp: December 20, 2012, 10:03:37 pm
content: Quote from: ee851 on December 19, 2012, 09:45:35 pmare you sure??have you did some measurements? ("Only dissipates 6.3W")

author: IanB
author_rank: Super Contributor
timestamp: December 20, 2012, 11:05:27 pm
content: Quote from: Alex on December 20, 2012, 08:20:30 pmThat looks neat. It is a steady state simulation I presume? Concerning the assumptions, do we have the plate suspended horizontally in free air with natural convection, and perhaps neglecting heat transfer by radiation?

author: Alex
author_rank: Regular Contributor
timestamp: December 20, 2012, 11:23:56 pm
content: Quote from: IanB on December 20, 2012, 11:05:27 pmHi Ian,You are right, this is steady state. The plate is in no particular orientation, however the convection cooling coefficients for each face were selected to be representative of a horizontal plate in free, otherwise stationary air.Heat loss due to radiation was included,but using black body characteristics.Other important assumptions are that the LED is perfectly coupled to the heatsink (no R c-s) and that it has a diameter of 2cm.Alex