Heatsinking

[davedent]

I'm in the process of making a headlight for dentistry. Plan to run 1 CREE Q5 at either 350 mA or 750 mA. Diameter of the base of the unit will be 20mm just wondering how thick the alu bar heatsink should be. Ballpark suggestions or more accurate advice would all be greatfully received.

Dave

 

[ambientmind]

what is the headlamp going to be made out of? is it plastic, aluminum, those funny things you bite onto for x-rays? lol. at 350mA you dont need much of a heatsink at all, at 750mA, things might get toasty on your forehead. so you might want to have some sort of insulator between the heatsink and your dome. some more info on your design would be helpful. good luck!

EDIT: after thinking about it, i wouldnt run the led at more than 350mA. at that current, youll still be getting just over 100lm from the led which in itself is pretty bright for close up work. 750mA would give you something like 175lm which would just blind you especially if someone had some nice pearly whites.

 

[jeffosborne]

The answer depends on what upper temperature you desire or can tolerate. To keep it at 'room temperature', you need 10 square inches per watt! If a 10 degree rise in temp is okay, less surface area can be used. Also, is this for continuous duty, or on a few minutes at a time?

I have a continuously running LED at 270ma that has about 4 square inches of aluminum bar exposed to free air, and it is mildly warm. 750ma will require more surface area than I would want on my forehead. Perhaps a tiny fan is in order for that current level.

Hope this helps!

Jeff O.

 

[eebowler]

I'd answer by simply saying that you should take up as much space as possible with the heatsink. In my opinion, what's just as important is how you're connecting the LED to the heatsink. Direct connection of the LED to the heatsink with thermal epoxy is IMO the best thing to do as opposed to having a star( or round base) heatsink in between. The lower the number of thermal junctions between die and air, the better.

If you want, take a look at the Princeton Tec Apex for ideas. There are lots of pictures in threads here.

 

[davedent]

Thanks for the info guys. Decided to run it around the 300 mA range. tried attaching LED to my proposed housing.. got very hot very quickly!
Havent decided what i'm going to make the final version out of yet.. probably going to be all aluminium.
just need a small cylindrical housing with an aperature at the front to fit the LED and lens. Drill hole in the side to thread the wires in and bob's your uncle!
Don't understand how a professional one costs upwards of £700.. i know they have to make a profit but thats crazy talk!

 

[eebowler]

If you're willing to spend less than half that amount, check out the Sten light Link 1 Link 2. It's one of the best headlamps you can find.


Aluminium is the best choice for a heatsink since it's 'cheap' and easy to machine.

How are you going to attach the light to your head? What power source are you going to use? Optics/ reflector?

EDIT: Neglected to mention that the sten light does not have normal straps for the head as yet. It looks like they are working on it though.