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Conundrum

Mon Aug 10 2009, 05:19PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hi all.
I got one of those 100W LEDs that TDU published a write-up about.

Was looking into using liquid cooling as it might make things less cramped.
Current plan is to use some surplus tin/lead plumbing solder (as its now banned from use for plumbing) and air con tubing as a cooling block.

Has anyone tried this? I did some tests and it seems that it should work (lots of small tubes = much heat flow) and making the contact area of the block from silver/tin alloy should improve the thermal conductivity.

regards, -A

HV Enthusiast

Mon Aug 10 2009, 05:59PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Do you have the link to the original write-up?
If so, please post it!
Thanks

lpfthings

Mon Aug 10 2009, 10:07PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

W LED

:)

...

Tue Aug 11 2009, 01:37AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

There is also a thread here on 4hv

that has more info.

In any case, soldering a few passes of copper tube to a block of copper should work well, although easier than putting the tubes in parallel is just using a few loops, and all other things constant you will have about the same amount of heat difference between the hot/cold end of the pipes.

Good luck!

klugesmith

Tue Aug 11 2009, 02:35AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Conundrum wrote ...

Current plan is to use some surplus tin/lead plumbing solder ... as a cooling block.

Has anyone tried this? I did some tests and it seems that it should work (lots of small tubes = much heat flow) and making the contact area of the block from silver/tin alloy should improve the thermal conductivity.

Are you talking about a 2-layer block of fusible metal: silver solder contact surface, backed by tin/lead that embeds the coolant tubes?
Ought to work, but wouldn't it be easier (and work better) to make your cold plate out of copper or brass, and solder the coolant tube on back surface? A rough contact surface, or other interference with thermal contact to LED module, would be more significant than which metal you use.

I'd suggest you make some simple thermal resistance calculations before cutting any metal. Look up the metal resistivity (degrees/watt * cm), multiply by heat path distance (LED interface to water), divide by heat path area -- that'll give you estimated degrees per watt. The conduction-cooling path wattage is probably between 1/2 and 3/4 of the electrical input power.

MinorityCarrier

Tue Aug 11 2009, 06:24AM

Registered Member #2123 Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312

Use something like these water-cooled copper heat sinks

Fraggle

Tue Aug 11 2009, 09:41PM

Registered Member #1526 Joined: Mon Jun 09 2008, 12:56AM
Location: UK
Posts: 216

It would be better to have a solid plate of copper, larger than the LED and a few millimetres thick, with the tubing soldered to it then clamped to the LED. I may have a suitable piece if you need it. If the water is too close to the heat you`ll have to pump it quite quickly.

aonomus

Tue Aug 11 2009, 10:10PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Think about using a vice to flatten the tube somewhat (filled with sand and curves already bent) so that the surface area of contact is larger. Otherwise, copper plate, and solder fill should do ok...

Tesladownunder

Wed Aug 12 2009, 04:31AM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Really a computer heatsink with attached fan is available at most computer shops and even a modest one will cope with the 80 W dissipation. Or get a heat pipe one that overclockers use.
Mine works fine except I smashed a blade and had to chip off opposing blades as a temporary fix.
Interesting that none of about 5 or 6 physicists guessed what it was when I showed it at the Uni Open day a few days ago. I usually like to bring along something that stumps the clever guys.

Proud Mary

Wed Aug 12 2009, 06:36AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Wouldn't iit be more prudent to use synthetic jets, a tried and trusted method of cooling LEDs of this size, rather than risk the diode burning up while these speculative cooling proposals are tried out on it?

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