Quote Originally Posted by voodoojnky
How hot does the heatsink get without the fan?

Don't know, actually.
That would be a costly experiment.
Led death is the upper limit with no airflow!

These leds are eating about 150 Watts.
Unlike most sources of light, leds do not radiate much heat with the visible light, so we have to dispose of the heat produced by moving it away from the emitters as efficiently as possible.
With no heatsink, these pups would pop in a fraction of a minute.
With a heatsink and no fan it would take a while, but the heat extracted from the emitters has to go somewhere.
If we don't remove it from the 'sink faster than we generate it, it's a matter of time before component failure.
I did run the first blush without a fan but after 5 minutes the sink had reached 100 degrees F. that's 20 degrees above ambient.
3. 80mm. muffin fans keep it under 90 F.

I've ordered several fans and will use the quietest one that does the job.
I'm still testing for creeping current now to see if I can safely run this without adding 12 Constant current drivers.
IF, it is stable with one central constant voltage source, we're done and will not need the dimmers or the CCs

My "brick" of 5 Watt emitters on a smaller heatsink had enough current drift to worry me so I re-did it yesterday adding 3 LM317 current regulators;

[attachment=o216168]

Slowed it's fan to about 1/4 speed and let it cook.
After 1 hour my heatgun said 120 F.
:microwave:
At 1/2 speed it's at 90 F. and still all but silent.
More than I can say for the Chinese UFO.

Today, I use the "brick" to play with lensing.:weedpoke:

Aloha,
Weezard