Heat sink for 9x1W emitters in fixture

[strandbygaard]

Hi,

Can I cool 9x1W emitters using a 6inch2 (150x150mm) piece of aluminum in a fixed lighting setup? Continues runtime willl be several hours per day.

I'm designing an LED replacement for an existing lamp fixture. I plan to use 9x1W emitters mounted on a heat sink, and trying to find out what "real life" requirements for such a heat sink is.

Using this calculator I've determined that 9W dissipated into a 6 inch2 (150x150mm) piece of aluminum (0.2"/5mm thick) would yield a heat sink temperature of 33C at 20C ambient.

Does that result seem reasonable?

I'm using generic 70lm/W emitters on a star pcb with Tj,max=125C from Ebay. I don't know the thermal resistance Tj,ambient, so I'm working from the assumption that it's the same as all other cheap generic 1W emitters (whatever that may be). Emitter lifetime should be at least 10.000 hours.

 

[jason 77]

Is this fixture your talking about enclosed or will the aluminum heat sink be in the open air? If it is enclosed then I don't think it will be enough.. That being said I have a 9 1watt LED light I made for my fish tank using some square aluminum tube about 3 feet long, and it has been running for about 10-12 hours a day for the past 3 or so years with no problem. The LEDs are in a semi enclosed light, it has two small vents one at each end.

 

[strandbygaard]

Thanks for the input.

The fixture is semi enclosed. The lamp is pretty open, but mounted on the ceiling.

It's difficult to see from the picture below, but the lamp is almost 4"/10cm high, and there is a .6"/15mm gap between the glass front, and the metal back. The metal back also has plenty of ventilation holes.

Assuming 1" square tube, that's about 0.1m2 which is at least twice the area of my plate...

I'm going to make a jig with a resistor on the alu plate in the lamp, and see what the C/W of the enclosed plate is.