Gryloc
Enlightened
You said that the light got hot to the touch. Did you mean the entire heatsink, or did you put your fingers on the LED emitter itself? If the heatsink is getting warm, then how big is this CPU heat sink? I know some laptop heat sinks are tough, but if you get one from an older, less powerful laptop, it may not be big enough. How much space do you have for a heatsink? How about a desktop CPU heat sink?moon lander said:yes im using a big laptop cpu heatsink, and no it is not sufficient. the light does warm up considerably. after about 15-20 minutes it approaches "too hot to touch".
If the LED is getting very warm, but not the heat sink, then how well did you attach the LED? (Thermal paste, screws, epoxy, thermal tape?). As long as you got good thermal contact, then you are just limited to heatsink size and the amount of current you use. LEDs are pretty rugged, they aren't living, so a little extra heat will only reduce the brightness (because of the phosphors) and shorten its life fractionally (I bet you will replace this with brighter and greater LEDs in the near future, anyway he he he). I should take that back. Maybe they are living since I care about LEDs so much . Luckily they are getting cheaper and it won't be the end of the world if they lose 10% of their brightness over a year or two. I don't know. Oh, I am sure a nice sized aluminum or copper plate will work, too. Its low profile and has decent surface area.
Do you have the resistor close or in contact with the heat sink? That may hurt performance. If you worry about the resistor, just support the resistor(s) up by the leads so there is air underneath it and it is isolated from the wooden cabinets. I have purposely used a 10 Ohm 10W ceramic resistor (with the exposed coils on the one side) to put a heavy load on a small lead acid battery. The coils got red hot, but the ceramic outside was fine as it was held in the air. It never did ignite (even after 10 min of this burn). I am so cruel. It never hurts to put a small 1A low voltage fuse in line with the output of the transformer. Keep heat managed, use heavy enough wire, and maybe use a fuse, and it should be worry free. Does this sound right?
Anyways. Crees are nice choices for interior lighting. I use three in a small desk lamp and is bright white and wonderful. The narrower beam pattern is very nice, too. Well, good luck and have fun with them.
-Tony