power LEDs- using the frame as a heat sink?

SniperGaulois

SniperGaulois

10 kW
Joined
Jan 31, 2008
Messages
797
Location
Rhone-Alpes
yesterday I have tested 3x 7w K2 leds which is the same as a 40w lightbulb, and the only way to keep them cool is a fatty CPU heat sink because that's how much heat they generate!
so it's tempting to uncover a piece of aluminium under the handlebars and glue them on with Arctic Silver epoxy and plenty of regular epoxy.

10kg alu heatsink!

is it possible that the metal will expand and cause problems and the paint will crack?

well I have just written all this and realised I could only have lights on one bike this way. darn!
 
Let's see the LEDs!

If you want to use the frame as part of the heat sink, the thickness of aluminum between the heat source and heat sink needs to be very thick. Other than the noise, a CPU cooler should work fine.
 
Hopefully the heatsink without the fan will be enough to cool it? That'd suck to have bought very efficient lighting only to have a fan sapping away your battery life.
 
Some of the Chinese clone types are rated as 7 watts.... Some of them actually achieve it if they are harshly overdriven. I have some old 3 watt Luxeons that are running at about 6 watts, but they are very well heat sinked (sunk?) (Sank/) ;) and rarely run for more than 20 minutes at a time; usually only a couple of minutes.

I'm not sure that using " a piece of aluminium under the handlebars" would do the trick. You need something either fairly massive or something with a lot of surface area. The fortunate thing is that the moving bike can provide enough passive airflow to cool them just fine with smaller heatsinks. You don't need a fan unless you do a lot of standing still with the light on.

I highly recommend Arctic silver... That's what I have used on just about all of my high performance LED lights. But don't use regular epoxy at all. That will just insulate things.

This is the basic concept I'm going to use for my next bike light head, (using the very bright, efficient Cree and/or Seoul LEDS)...although I'm going to make it so I can easily remove it and use as a multi level , multi lens patterned flashlight/spotlight too:
http://www.racedaynutrition.com/features/bikelight.aspx
 
hey you are completely right about that, it's 5w, although there is a light called the ostar which is 15w http://uk.farnell.com/jsp/search/browse.jsp?N=500004+1000028&Ntk=gensearch_001&Ntt=ostar&Ntx=v

generally the aluminium would be over 3mm in the frame itself...I mean under the handlebars in the actual diamond frame tubes! where the badge of the bike make is.

maybe I have planned the lights wrong because I'm driving them at 90% maximum power, which maybe generates a lot more heat than going at the 50% of the range, it's just that I have ready-made electronics that do this...it would take about 2 minutes to raise a processor heat sink without airflow to about 70°C I reckon!

probably it's reasonable that you have to allow for at least five minutes of standstill without the lights overheating...just as a safety margin.
 
I think it is a very good idea to use bike frame parts as heatsinks for many ebike applications not only LEDs. With K2 LEDs specifically you need to insulate the LED base from the heatsink. There are many insulating thermal pads available - check digikey. Alternatively arctic silver (as already mentioned here) makes thermally conductive insulating epoxy but you have to make sure there is a tiny gap between LED base and HS when epoxy is setting.

You can also use a metal clamp to the handle bar as an intermediate platform. This should make it portable. Also the contact area between the clamp and the bike can be pretty large and the thermal resistance is not near as critical as between the LED and the HS.
 
As many great lights as I have built with Lumileds products, I have to say that Crees and Seoul LEDs often leave the K2s in the dust for brightness and efficiency.

I've been buying them from here:
http://www.kaidomain.com/WEBUI/SubCategory.aspx?TranID=8249&Name=Flashlights-DIY
They have a very large selection of LEDs and other parts useful for building your own lights: Reflectors, optics, circuit boards, complete modules to make building your own light easier.
They even sell those 15 watt Leds.
Plus tons of other neat stuff at great prices.
If you are not boycotting China and don't mind sometimes having to wait a week or two or three for delivery, I can highly recommend them.

If you get confused by all the different choices, this place can help
http://www.candlepowerforums.com/vb/forumdisplay.php?f=91
http://www.candlepowerforums.com/vb/forumdisplay.php?f=17
 
Are we talking about different parts perhaps ? Check the datasheet p13, note 1 for fig 1:
http://www.lumileds.com/pdfs/DS51.pdf
 
Maybe you are talking about K2 star ? That is a different story. I've used plain K2 in the past not the stars.
For the star the thermal conductivity of adhesive is nowhere as critical as for the raw LED. As long as it is thin plain epoxy should do just fine IMHO.
 
have just fixed on 15W of K2 emitters to the bare aluminium of the frame with Arctic silver alumina adhesive, which turns out is pretty strong stuff, and the lights stay way cool! the frame immediately around the emitters goes all the way up to 23°C, and within a few inches it's back to 12°C, the ambient temperature of the garage... excellent!
 
okay it seems that the slugs should not be connected electrically, I obviously got a reference mix up
http://www.lumileds.com/pdfs/AB29.pdf
Similar to the LUXEON I, III, and V, the slug of the LUXEON K2 must be electrically isolated from the anode, cathode, and other
slugs. This requirement stems from the basic internal construction of InGaN LUXEON K2 devices
 
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