Heat sinking LED arrays

[X-CalBR8]

I had (what I think to be) a great idea for a LED array heat sink and thought I would take the time to share it with the class.

I thought I would Epoxy Pennies to the back of the circuit board and then drill holes through the spots that the LEDs would stick through and then solder them on the back. The old Pennies are made of pure copper and should prove no problem to solder to and should (theoretically) act as a very good heat sink. If the pennies should touch in any undesirable place, simply take the trusty Dremel tool to them and cut them up. I don't know how I ever got by without a Dremel tool. Very handy! About the only metal that will conduct heat better than copper is Silver or Gold, and that's not gonna happen. LOL. The way I figure it, the whole heat sink should only cost between $.05 and $.10. A hard price to beat.

How about it? Anyone else kicking around any ideas for heatsinking your LED array? I thought it would be nice to have a thread devoted to heat sinking just to see what new ideas could be garnered on the subject.

 

[Elmie]

I have been looking into heatsinking my 18 led Double Barrel. I still don't know what to do. It does get pretty warm when left on for extended periods of time.

 

[The_LED_Museum]

Interesting idea - for those who have a dremel tool at their disposal.
Maybe I'll ask pops for one for Christmas this year.

 

[Silviron]

I read a study about 3-4 years ago that blackened copper(painted or oxide coat) was the best heat sink material available (barring peltier or other refrigerated devices of course) Better than aluminum, better than gold, even better than silver.

(In case anyone thinks of trying : Do NOT try using titanium for a heat sink - it is one of the worst metals for thermal conductance!)

If I remember correctly shiny copper was just a tiny bit more thermally conductive than aluminum according to this study (which was done by either Intel, AMD or Cyrix in an attempt to control heat in the earliest Pentium type CPUs).

Don't ask me why the blackened copper is supposed to be better- It didn't make sense at the time, and still doesn't to me. In fact, if the black heat sink were exposed to sunlight etc. it could absorb that heat and transfer it to your component!.

Anyway, I have heat-sunk a couple of things using copper, (including pennies) - Works great, blackened or not. If a penny is a convenient size for your purpose, go for it.

Be sure you use a pre-1982 cent- the copper coated zinc ones could possibly set up some weird galvanic action in your circuits ;-)

To insulate the lead that you DON'T want connected (or shorted, just run a "sleeve" of heat-shrink over it. (I also have been known to use clear nail polish for quick & easy lead insulating when I don't have any "professional" stuff around.

 

[**DONOTDELETE**]

Hi Guys!

The cause why blackened bodies can get rid of more heat is they can emit infrared waves better than non-blackened (also they can take these waves better f.e. in the sunlight). This is why most aluminium cooling bodies are coated with a black anodizing.

But for cooling LEDs f.e. in a 18LED double barrel I think a plate of copper would be enough. It will spread the heat away from the dice of the LEDs and this should be enough. If you would like to cool the whole Lamp, you would have to improve the surface of the lamp OUTSIDE, which should be rather difficult (and not very preatty). The aim is to make the temperature DIFFERENCE between the LED dices and the lamp smaller.

My fafourite cooling is a plate of copper in size of the LED array with small holes for the cathode and large holes for the anodes. Then a layer of PCB with large holes for the cathotes and large holes for the anodes is glued on its back. Now you can solder the cathodes onto the copper though the large holes of the epoxy and the anodes to the copper layer of the PCB. Now the common cathode is the copper slice and the common anode is the PCB.
This provides enough area to spread the heat of a 36 LED array. Even if the whole thing gets REALLY warm (up to 60-70 degrees celcius!), the LEDs are in the safe area.

Bye!

 

[Silviron]

AHA! that makes sense- Infrared emissions.

Thank you!

 

[**DONOTDELETE**]

Regarding using a large copper plate for heatsinking the cathodes:

If it is fairly thick won't it take a lot of heat to bring it up to soldering temperature? I would be afraid of melting the LEDs or seriously overheating them since it would be nearly impossible to do a really quick job of it. And of course the cathodes would be trimmed too short to use a hemostat to protect the LED during soldering...
I was under the impression the LEDs could only tolerate soldering temperatures for a couple of seconds- heating up a relatively large copper disc would lengthen that considerably. So I guess my question is: what gauge copper are we talking about here?
Chet

 

[X-CalBR8]

How about using silver paste? That's what I'm gonna try to use when soldering some SMDs together. You just heat it with a heat gun or very quickly with a small torch. The stuff that I was reading about it says that it is supposed to dry harder than solder. I hope to have first-hand experience with it soon so I can pass on more details about it.

 

[Silviron]

As Bart Simpson would say-

"HEY, No Problemo Man!"

Here is a "Quick & dirty" job of two parallel connected Nichia 5.6CD LEDS with negative leads soldered to a penny, the positive leads insulated with heat shrink.:

<IMG SRC=http://www.az123.com/LED/pennyled1.jpg>

<IMG SRC=http://www.az123.com/LED/pennyled2.jpg>

<IMG SRC=http://www.az123.com/LED/pennyled3.jpg>

I WOULD recommend that you pre-tin the leads and the connection holes in the penny though.

I'm a "Ham Handed" solderer most of the time, so If I can do it, anyone can.

I'm not sure if it would be better to cool the unit between the soldering of each LED or not- I did on this one, but it did make it harder to get a good solder joint on the second lead. (Your results may vary!)

It does seem to be working pretty well- the penny is running (right now 40 degreesC (7 degrees hotter) than the LED cases where they contact the penny; The unit is drawing 80mA at 3.75 volts

 

[Chris M.]

Interesting idea with the coin. But- I`m sure I heard that in the UK, it`s actually illegal to mangle the currency like that- even pennies? So, UK viewers at least, I`d suggest finding an alternative source of copper. Shame cos the coins are often the right shape or size, but there you go...

 

[Silviron]

Here is the info on legality in the US:

"The United States Codes under Title 18, Chapter 17, and Section 331, "prohibits the mutilation, diminution and falsification of United States coinage." However, it has been the opinion of individual officers at the Treasury Department, though without any indication of approval, the foregoing statute does not prohibit the mutiliation of coins if done without fraudulent intent or if the mutilated coins are not used fraudulently."

There is a long tradition of mutilation of coins in the US- in fact there is a specialized area of numistmatists that collect "squooshed pennies". Squooshed pennies web page


Even if it were indeed illegal in every country to deface or mutilate their coinage- we could just swap!!

Send me some Euros and I'll send you some pennies ;-)

 

[Badbeams3]

Poor pennies, they just do not get respect...at Bush Gardens and Disney World you put a penny in a machine and crank it...out comes your flatened out coin which now say`s Bush Gardens 2001 or Wilderness Lodge 2001...in keeping with the US way of life...it cost you a quarter to mutilate your penny into a worthless souviner.

 

[Go Go Gadget Flashlight]

RE: Mutilated coinage...

OK, then what about plumbing copper.

Take a piece of tubing, slit it lengthwise, then uncurl it and flatten it out. Viola! (pronounced "vie-owe-la")

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Phantomas'

My fafourite cooling is a plate of copper in size of the LED array with small holes for the cathode and large holes for the anodes. Then a layer of PCB with large holes for the cathotes and large holes for the anodes is glued on its back. Now you can solder the cathodes onto the copper though the large holes of the epoxy and the anodes to the copper layer of the PCB. Now the common cathode is the copper slice and the common anode is the PCB.
This provides enough area to spread the heat of a 36 LED array. Even if the whole thing gets REALLY warm (up to 60-70 degrees celcius!), the LEDs are in the safe area.<HR></BLOCKQUOTE>

So far, I like Phantomas' "sandwich idea" best whether using pennies or tubing.

 

[Silviron]

Yeah, I was going to suggest copper plumbing fittings the other day too, but that IS kind of a hassle- if all you need is a simple disc of metal- Slitting tubing, flattening it etc. is a PITA even with the proper tools.

Just buy some sheet copper if you don't want to waste a lot of time shaping metal- it isn't ALL that expensive if you go to the right source. Or better yet, suppliers for hobby enammeling sell pre-cut copper in a variety of shapes. Here is one that I have purchased from before: http://www.metalliferous.com/

Go ahead and use a coin- I won't tell ;-)

Plumbing fittings CAN be a good construction material for custom lights though- Here is my first prototype for my Caving / mining light with 6 LEDs in it:

{P.S. KEN- A quarter to "squoosh" a penny is a good deal- MOST penny squishing machines cost 50 cents (plus your penny) and some are 75 cents or a dollar}

 

[X-CalBR8]

Silviron: Great job with the heat sink. That's just the sort of think that I had in mind except that I had in mind to epoxy the penny to the back of a circuit board so that the LEDs would have a flatter surface to sit on. Still for only 2 or 3 LEDs I think I may like your way best. I've got a light that I wanted to convert to 3 LEDs and I think I will try the way you did yours. Congrats on the cool Penny mod.

 

[Steelwolf]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by KenB:
Poor pennies, they just do not get respect...at Bush Gardens and Disney World you put a penny in a machine and crank it...out comes your flatened out coin which now say`s Bush Gardens 2001 or Wilderness Lodge 2001...in keeping with the US way of life...it cost you a quarter to mutilate your penny into a worthless souviner.

<HR></BLOCKQUOTE>

It cost you only a quarter?!?!?

I've been ripped off. Waaaaaayyyy back in the mid-eighties, I went on a trip to Seattle and visited the "Space Needle". Cost me US$2 to get my penny squooshed. Nice picture of the place though. Still have it somewhere.

You guys ever heard of a heat pipe or thermosyphon. Very messy to make and implement because it uses liquids to move the heat convectively, but, if properly designed, can move prodigous quantities of heat. Probably not worthwhile unless you're trying to pump 80mA through each LED, and only if you have an array of 30 or more LEDs.

 

[Quickbeam]

Just a suggestion, instead of soldering, why not use thermal conductive grease to span the gap between the LEDs and the copper plate. - That's how the heat is being transferred between your computer's processor and it's heat sink - Plus it will give additional waterproofing and corrosion resistance to the metal parts.

 

[Silviron]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by X-CalBR8:
...except that I had in mind to epoxy the penny to the back of a circuit board so that the LEDs would have a flatter surface to sit on...<HR></BLOCKQUOTE>

I can see where a flatter surface would be nice, although not sure it makes any "real" difference.

If it DOES make a difference to you, get a sheet of 220 grit sandpaper, put the sandpaper on a smooth, flat, hard surface (formica countertop will work fine) and just rub the penny back and forth & around on the sandpaper for about 5 minutes- It will be as flat as if it were machined by a surface grinder.

(You may have to dip it in some water to cool it every 30 seconds or so- IT can get uncomfortably hot if you are rubbing vigorously.)

I can see where the circuit board "sandwich" could be GREAT for complex applications, but just to heatsink 2-3 LEDS, I don't think I'd bother.

Wouldn't it be cool though if you could make the "sandwich" mount your LEDS and put a SMD voltage regulator / switcher "pump" all on the board?? Beyond MY abilities for sure.

 

[Silviron]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Phantomas2002:

...If you would like to cool the whole Lamp, you would have to improve the surface of the lamp OUTSIDE, which should be rather difficult (and not very preatty). The aim is to make the temperature DIFFERENCE between the LED dices and the lamp smaller...<HR></BLOCKQUOTE>

I'm not sure if it is at all practical, and it certainly wouldn't be if you are going for compactness OR longevity, but I have been thinking that if you are over-driving your LEDS (& any other circuits) you COULD add a fan if you have enough room and extra power. Hosfelt has a 5V, 1" square fan at:
http://www.hosfelt.com/Fans/5vdc.htm

 

[StuU]

Another use for copper plumbing parts is to construct a copper PR base with greater heatsinking abilities. I have made several PR bases out of 1/4" plumbing parts into which I have soldered 3 leds with individual dropping resistors.

Use 1/4" copper pipe for standard size PR bases. Use a nylon hex-nut for the insulator - file to near size and press in. The positive is a brass screw of the nylon nut size. It works well to drill a 1/16" hole in the hex nut into which the + leads will be drawn and soldered. Solder the negative into 1/16" holes drilled into the side of the base.

The rim is constructed before emplacing the leds. Use #14 copper wire formed around the top of the PR base, held in place with hemostats or vicegrip, and also soldered. File to fit the mag socket.

Use the 1/4" junction(larger) for a bigger base which will fit the maglite perfectly. This base is capable of holding 3 1/4 watt resistors(or even 1/2watters). and 3 leds.