How much heat dissipation would nine 1W LEDs need?

[pensiveone]

Hello folks.

Planning on doing a DIY light fixture for a new 1.2 gallon pico reef project I'm starting soon.

 

http://www.chicagoreefs.com/forums/showthread.php/25345-My-1-2-Gallon-pico-build

 

I have this metal box I got from a Habitat for Humanity Restore that I plan to use (see pics below). It looks like it was intended to be used for some type of Exit sign I think. Very solid with a gray industrial quality finish. It has a bottom plate of sheet metal that has a white finish on it. I am planning on adding 9 1W Led which are attached to those little star shape PCB. Since they will be mounted directly to the metal plate, would that be sufficient heat dissipation? If not, how much more would I need. I was also planning on adding a sheet of glass to the opening (there are tabs inside that look to have been intended to hold a sheet of glass in) but would that cause too much heat? Thank in advance!

[evilc66]

The general rule of thumb is 10 square inches of surface area per watt for passive cooling, but that's under the assumption that aluminum of doing the cooling. That box is most likely steel, so it's not nearly as effective at getting rid of the heat. You can always try it and monitor the temperatures. If it doesn't work, then you aren't out a lot of time and money. But you really will need to test it out before you commit to putting it over the tank.

[pensiveone]

The general rule of thumb is 10 square inches of surface area per watt for passive cooling, but that's under the assumption that aluminum of doing the cooling. That box is most likely steel, so it's not nearly as effective at getting rid of the heat. You can always try it and monitor the temperatures. If it doesn't work, then you aren't out a lot of time and money. But you really will need to test it out before you commit to putting it over the tank.

Thanks for the advice! It is only 56 square inches so that is not enough for nine LED. I suppose I can attach a sheet of aluminum to the sheet metal to increase the heat transfer. Still need to add something to help it cool. What are my options? Could I add some thing like say a computer heatsink to help cool the metal? Or would I need a fan? My other option is to use some 9" T-5 bulbs I have and make it fluorescent instead...

[evilc66]

You won't want to just attach some aluminum to the case, as you aren't solving the problem of thermal transfer. The steel will always be the bottleneck. Best thing to do would be to find an aluminum heatsink, cut out an appropriate hole in the case, bolt the heatsink to the case and attach the LEDs directly to the heatsink.

[Caravanshaka]

You won't want to just attach some aluminum to the case, as you aren't solving the problem of thermal transfer. The steel will always be the bottleneck. Best thing to do would be to find an aluminum heatsink, cut out an appropriate hole in the case, bolt the heatsink to the case and attach the LEDs directly to the heatsink.

This is what I am doing in my ATI sunpower. I have some heatsinks that I will be cutting a hole in the steel to bolt the heatsinks to.

 

With that size fixture, you should be able to get a heatsink pretty cheaply

[pensiveone]

Okay, I think I am understanding now. The LEDs need to be directly attached to the heatsink. I am planning on using 20mm star PCB, so I could :

 

1. Drill a 1" hole through the sheet metal for each LED,

2. Attach the heatsink over the openings,

3. Attach the LEDs on the PCB directly to the aluminum heatsinks.

4, Wire together the LEDs and connect to power supply.

 

Another option would be to replace the entire sheet metal bottom with an aluminum sheet instead. Then I could simply attach the LEDs to that sheet of aluminum and add a heat sink to the aluminum bottom. Make sense?

This is what I am doing in my ATI sunpower. I have some heatsinks that I will be cutting a hole in the steel to bolt the heatsinks to.

With that size fixture, you should be able to get a heatsink pretty cheaply

 

It is only 6 inches by 9 inches. I was looking at this one on e-bay, but I would have to cut it in half.

 

http://www.ebay.com/itm/Aluminum-Heatsink-Heat-Sink-Cooling-for-4pcs-x-3W-12pcs-x-1W-Leds-Light-Lamp-/190895630373?pt=LH_DefaultDomain_0&hash=item2c72442825

[Caravanshaka]

Those options should work.

 

I would suggest getting two 2"x8" heatsinks since strip heatsinks are fairly cheap and easy to cut.

[evilc66]

Okay, I think I am understanding now. The LEDs need to be directly attached to the heatsink. I am planning on using 20mm star PCB, so I could :

 

1. Drill a 1" hole through the sheet metal for each LED,

2. Attach the heatsink over the openings,

3. Attach the LEDs on the PCB directly to the aluminum heatsinks.

4, Wire together the LEDs and connect to power supply.

 

Another option would be to replace the entire sheet metal bottom with an aluminum sheet instead. Then I could simply attach the LEDs to that sheet of aluminum and add a heat sink to the aluminum bottom. Make sense?

 

 

It is only 6 inches by 9 inches. I was looking at this one on e-bay, but I would have to cut it in half.

 

http://www.ebay.com/itm/Aluminum-Heatsink-Heat-Sink-Cooling-for-4pcs-x-3W-12pcs-x-1W-Leds-Light-Lamp-/190895630373?pt=LH_DefaultDomain_0&hash=item2c72442825

Both options will work well

[Benny314]

That box looks quite deep.

 

I would find a heat sink that fits in the box, mount your LEDs to the heat sink and then use the space in the box to hide all your wiring, place a fan or 2 in the top of the steel box with holes cut in the box allowing the fan(s) to draw air.

Then set the heat sink to fit flush to the fan(s) and finally add a splash guard at the opening of the box and you have a supper sleek looking light fitting.

 

My thoughts anyway.