Lamp heatsink calculations

Barkuti · 2019-04-10T16:40:47.000Z

I am to build a lamp based on the following:

A 300 × 140 × 20mm main aluminum heatsink conjoined with two 300 × 25 × 12mm 30° bevel wing heatsinks. Each wing will bear up to 10W of power, with the main unit dealing with up to 50W (10S emitters at ≈1.5A).

Is this too much power for it to work at a reasonable temperature? According to this MyHeatSinks calculator:

It is just 0K at best. I am thinking in attaching a few low power small fans to it but, what do you think?

Thanks for your colaboration. ;-)

:-)

kikkoman · 2019-04-10T18:12:21.000Z

Do you know which emitters you’re going to use and their junction-to-case resistance?

Barkuti · 2019-04-10T18:25:53.000Z

LH351D emitters reflowed on 20mm copper 3535 DTP boards but other than that no idea, found no figures. They should be pretty close to XP-L or XP-L2 ones.

^:)

kikkoman · 2019-04-10T19:26:54.000Z

Ok then we can assume ~2.5°C/W junction-to-heatsink (2.2 junction-to-solder point from datasheet, + a generous 0.3 for DTP and thermal interface), so at ~5W each junction will sit at ~12.5°C above ambient (“ambient” in this case is the heatsink temperature).
So even the smallest fan will work without overheating (Tjmax is 150°C) but you’ll get less output than what they’re binned at (at 85°C) and you’ll have to derate your output calculations accordingly.

Watch this

Barkuti · 2019-04-10T20:46:00.000Z

Thanks for adding some light kikkoman. Will buy a set of six thick 12V 6cm fans and make 'em work at 5V for super silent cooling, two at the wings leaning into the main, and 4 at the main. That should keep the stuff cool enough while being silent and reliable.

^:)

snakebite · 2019-09-23T19:25:09.000Z

if 50w is the input your heatsink will be fine.
as not all 50w is dissipated as heat.
and using newer tech leds like you have it just gets better.
might be able to run passive.
better for efficiency and reliability.
no fans to fail.

Barkuti · 2019-09-23T22:23:03.000Z

Right on cue snakebite. But this stuff got cancelled after my friend spoke with me about the mandatory “product specifications”. See: Flush ceiling light overhaul heatsink calculations. Will right now update the thread for the sake of it.