cree.... how hot is to hot

[Axkiker]

So I have been screwing with some casting materials and trying to find one which can be used as a heat sink.

I have a material which contains alot of aluminum powder and is actually intended to dissipate heat. Now im sure that being it only contains a portion of aluminum that its not as conductive as a true aluminum heatsink. So im curious how hot is too hot for one of these cree leds and how do you check.

I have one of them attached to a piece of the machined casting material with arctic thermal paste and it runs continuous without an issue. However I do notice that the little bugger is HOT

any way or idea how to check if its within operating range. I thought about getting one of those laser thermometer deals but even with that you cant really check the back thermal pad.

ideas????

 

[The Dane]

@ 700mA max led die temp = 35 degC
@ 600mA max led die temp = 50 degC
@ 400mA max led die temp = 80 degC

http://www.led-tech.de/en/High-Powe...CREE-XR-E-7090-Q5-Emitter-LT-1144_120_77.html

Data found in gallery thumbs in the middle of the page.

 

[Steve K]

I have one of them attached to a piece of the machined casting material with arctic thermal paste and it runs continuous without an issue. However I do notice that the little bugger is HOT

any way or idea how to check if its within operating range. I thought about getting one of those laser thermometer deals but even with that you cant really check the back thermal pad.

ideas????

a rough rule of thumb: If the LED isn't dead, then it's not too hot.

An extension of this rule is that the temperature is inversely proportional to its lifetime. The warmer the LED is, the shorter the lifetime.

I have one small bike light that I use infrequently, and if the bike is stopped, the heatsink does get fairly warm. With the limited time that the light is on, and the limited time that it is actually fairly warm, the reduction of lifetime is worth more to me than what it would take to increase the size of the heatsink.

On other lights, I provide enough heatsink to keep the leds from even getting noticeably warm. These are lights that I use often, and I consider to be critical to safety.

Other considerations: design the heatsink for the worst case condition. Will it be used when the ambient temperature is high? i.e. will it be used on a hot summer day, or in a very warm environment? Have you considered any local heating that might be caused by the voltage regulator, especially under high input voltage conditions? Will it be used with limited air flow (i.e. will it be partly covered?).

Hope this helps provide some understanding of the issues....

Steve K.

 

[snarfer]

Don't know if you could use a thermocouple. But they are cheap and easily obtained.

Is the material from Coolpolymers? I was looking at that.