Outdoor Heatsinking Idea

[JamisonM]

My grandmother has a flag in her front yard that she leaves out 24/7. I've asked here about making here an LED light that will illuminated it at night. I've thought about different ways to go about it, but they all revolve around a single LED or 3 LEDs on a MCPCB with diffusing lens. Either way I do it, It will require heatsinking of some kind. I thought about taking an old Pentium 4 heatsink and mounting them on it. Something else I thought of is taking a piece of 3ft long 1" copper pipe and flattening 2"-3" on one end. This will be the end that the LEDs will be on and will be bent to a slight angle. It will be driven into the ground 3/4 of it's length. My idea is that since the ground is usually much cooler than the air in the summer, it will give the heat from the LEDs a place to go. I wonder how well this would work and would like to hear everybody's thoughts on it. Thanks!

 

[Lynx_Arc]

I'm thinking that earth is more of an insulator than a conductor. It tends to store up heat and slowly release it rather than pass it on so that heat would more likely build up in the earth right around the LED itself than pass the heat on farther away in the dirt.

 

[deadrx7conv]

If you have adequate heatsinking without the ground, then it'll work well in the ground. This is a great idea that you should test yourself.

 

[JamisonM]

Sorry guys, I don't know where my mind was. For some reason, I thought this was the Fixed Lighting Forum. Can a kind Mod please move this thread? Thank you.

 

[Ken_McE]

I find that I must disagree with the otherwise fabulous Lynx_Arc. The earth can absorb massive amounts of heat. I believe that three or nine, or however many watts of LEDs the OP has in mind will have no noticable effect on the soil they connect to. Even if they did, the pipe will radiate heat to air, and the ground will have ~12 hours a day for the heat to disapate.

I seem to recall that Blasterman has a vaguely similar design for stage lights that works while it is up in the air, even without the advantages of the earth.

 

[Lynx_Arc]

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
Look up thermal conductivity of earth vs aluminum or any type of metal.
Oh.... BTW.... I'm not fabulous LOL
just another flashlight dork here not quite up to the geek level yet it costs too much ;)

 

[VegasF6]

I don't think the heat will radiate down much anyhow, it wants to rise. Maybe a few inches. The trick is going to be getting that pipe flat enough to make decent contact with the leds. I often use copper plumbing caps for leds. Perhaps you could solder up some sort of manifold and mount them to the cap ends.

 

[blasterman]

Heat only 'flows up' if due to natural convection like air. In a solid material thermal transference doesn't care about gravity.

1" copper pipe is superb as a heat sink. It's mounting stars to it that gets tough. Local shop sells 2" alu pipe cut to order. Works even better.

 

[alpg88]

I don't think the heat will radiate down much anyhow, it wants to rise..

it will, heat doesn't rise, hot air does, heat goes to where it is cold.

 

[VegasF6]

Yah? Neat.

On a sort of related note, is there a limit to how long that length of copper pipe should be before the excess is no longer effective? Or how much length before it touches earth? Would it be more effective to have it in air so it could radiate heat, or more effective in soil that may act as an insulator?
Would say a 6" by 6" square be more effective than a 1" x 36" bar of equal thickness?

 

[alpg88]

i wouldn't bother with earth, i would just find the bigest heatsink i could (or 3 separate, if you go with 3 separate leds), and mount those leds, old amps, and old server power supplies..ect, have huge heatsinks, i love taking apart those things, so much good stuff there.

i would think 6x6 would be more effective, but in theory they both have same aera, so they should dissapate heat the same, but real world is a bit different. so my guess is as good as yours.