Star v Emitter, Rebel, et al.

[minster9]

 :)Thanks for clearing things up a bit,cadstarsucks. I think the star-type units offer a major advantage simply because their thermal pad is so much bigger & thicker to begin with. Using vias on sandwiched pc board to get to the heat sink on the other side,blech!

[justDIY]

that being said, then the advantage goes to Edison opto instead of Phillips rebel, regardless of the fact the rebel may actually be the better performer ... the "luxeon" emitter type package can be "star" mounted, making it easier to work with, at least for the general hobbiest.

[cadstarsucks]

that being said, then the advantage goes to Edison opto instead of Phillips rebel, regardless of the fact the rebel may actually be the better performer ... the "luxeon" emitter type package can be "star" mounted, making it easier to work with, at least for the general hobbiest.

True enough.  They actually make the stars for the small manufacturer because it takes so much special equipment to use LEDs that can't take the heat of reflow.  The rebels seem like they can be handled by hand soldering on copper sheet with access holes for the actual contacts. 

While I have access to the equipment to officially solder them, that is somewhat defeating the purpose of hobbyist use.

The Rebel CAN be star mounted...It is just that they will not bother since while WE would like them as stars, the bulk of the sales that they make do not require it.

Dan

[justDIY]

any good (inexpensive) sources for copper sheet?

[minster9]

  Go to Enco,look in raw materials,& then shim stock. They sell brass shim stock (80% copper/20% zinc) in thicknesses from .001" to .030" in 6" wide rolls x 100" long. 10 or 15 bucks,depends on what you want. Been doing business with them for years. Had the aforementioned in mind for heat sink mtl. for the Rebels. 

[minimum]

Go to Enco,look in raw materials,& then shim stock. They sell brass shim stock (80% copper/20% zinc) in thicknesses from .001" to .030" in 6" wide rolls x 100" long. 10 or 15 bucks,depends on what you want. Been doing business with them for years. Had the aforementioned in mind for heat sink mtl. for the Rebels. 

No good. Brass' thermal conductivity is much worse than aluminium's:
http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

Brass 109
Aluminium 250
Copper 400
(W/m K)

[minster9]

  Didn't realize brass was such a poor conductor of heat. Maybe a person could chop up a junk automotive radiator? The end tanks are usually copper,aren't they?

[minimum]

The end tanks are usually copper,aren't they?

I don't think so - pure copper corrodes too fast. Might be brass(red/yellow) or some similar alloy.

[justDIY]

I remember seeing on a show "How its made", the end caps were stamped from sheets of copper and then coated with solder, then soldered onto the radiator body.  The fins and tubes are also copper, coated with solder.  The whole shooting match was then coated with asphalt (just the resin, not the aggregate).

[justDIY]

at the local lumberyard / home center they sell 12" x 36' rolls of copper flashing.  it is very thick material, and I'm not sure how pure it is (it looks just like copper).  it is also very expensive.

[minster9]

I seen that same episode of that show,thats why I suggested the idea. Scrap copper commands a couple bucks a pound around here,it would be nice to know someone who would let you whack a chunk out of the end tank of a junk radiator. You can easily flatten it out & cut it according to app. By the way, I love that show;they show some neat stuff!

[cadstarsucks]

I seen that same episode of that show,thats why I suggested the idea. Scrap copper commands a couple bucks a pound around here,it would be nice to know someone who would let you whack a chunk out of the end tank of a junk radiator. You can easily flatten it out & cut it according to app. By the way, I love that show;they show some neat stuff!

Now that sounds like some of the stunts I pull... At work I designed an RC car battery into a piece of industrial test equipment, the new version of this old thing - http://www.bidwellinc.com/powerdyne/boltgages.html; and at home I recognized at the dollar store that the spare razer wheels they were selling amounted to 8 sealed ball bearing sets for a dollar .

Dan

[minster9]

 :)cadstarsucks,I just remembered I have a small sheet of copper! If I recall,it's about an inch wide,8-10 inches long,& at least .030" thick. It's in my shed somewhere,just seen it couple days ago. I know it's copper because I got it from a microwave transformer or magnetron ,it was wrapped around something,can't remember for sure. It has a varnish-type coating on it & the ends are tinned;not near as shiny as brass. I'll have to dig it out & measure it. Reason why I didn't give a second thought to it is because I'm having second thoughts about the Rebels. Did the metric to decimal conversion thing;the thermal pad is .070"x.110". The electrical pads are .047"x.026"! I know you guys deal with objects this small for a living,but they present a challenge to me. And I don't really understand the math involved in Luxeons' pdf app. briefs,I never could grasp higher math. And the fact that 90% of the electrical power is being wasted as heat(the way I understood it) offsets the small size of the emitter vs. heat sink size. If a person soldered a .060" thick (about the thickness of a wheat penny with the faces milled flat) piece of copper having a half square inch of area onto a piece of copper half the thickness & 6 times the area,would that be sufficient? I would thread a couple screws through the radiator sheet into the intermediate copper slug after soldering, and then tin the side facing the led. Rig up (make) a spring-loaded guide jig to place the led thermal pad end onto tinned slug while still hot. Spray water mist after 3 seconds? Comments appreciated. (I'd rather have a bottle in front of me than a frontal lobotomy) Thanks,everyone,for your advice

[minimum]

If a person soldered a .060" thick (about the thickness of a wheat penny with the faces milled flat) piece of copper having a half square inch of area onto a piece of copper half the thickness & 6 times the area

That would make about 3 sq. inches of area. From the Lumiled's LED thermal design guide, the rule-of-thumb was about 9 sq. inches of area per one watt. So 3 sq. i. isn't sufficient IMHO. Besides, between two copper sheets you should apply something(thermal paste, etc) to transfer the heat.

[justDIY]

seems to be, the only way to handle a rebels heat is in 3D ... that is, a heatsink with fins, yielding enormous surface area while providing a small footprint.

if the rebel emitter is rice-grain sized, we'll want to pack a lot of them in a small area.  trying to give 9 sq. in. of flat pcb space to each one would result in really low density, and a really big project.