Re: Heatsinking a 3W Luxeon

In article <e8bbpc$r8l$3@xxxxxxxxxxxxxxxxxxxxxxxxx>, szekeres@xxxxxxxx (GregS) wrote:
In article <44a92152$1_1@xxxxxxxxxxxxxxxxxxx>, "Jason S"
<jst3712@xxxxxxxxxxxxxx> wrote:

"GregS" <szekeres@xxxxxxxx> wrote in message
news:e8b3vh$pmc$2@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
In article <44a8970d_1@xxxxxxxxxxxxxxxxxxx>, "Jason S"
<jst3712@xxxxxxxxxxxxxx> wrote:

"Stanislaw Flatto" <compaid@xxxxxxxxxxxxxxxxx> wrote in message
news:QtNpg.1598$Nv4.242519@xxxxxxxxxxxxxxxxxxxx
Jason S wrote:

So what you're saying is the thicker the better?

God forbid, never mentioned anything like this, we are on a group that
has
_design_ in its name, so I treat it as such. For every solution there is
some calculated result and you can use this as a minimum or add as much
safety factor as you wish, but know what you are doing.

Example: look at any manufactured heat sink, be it on your CPU or the
one
surrounding the piston on your "Harley Davidson". You will notice that a
lot of material is removed to create larger surface for more efficient
transfer of heat to air.

But the air has to flow freely, no magic about it.

That shouldn't be too much of a problem. You see, I got nowhere to put
a
fan, that's the reason why I'm posting this!

No need of forced air movement, enough surface of the heat sink in air
and
the warmer air will move up by itself to be replaced by the cooler air
from the surroundings.

Thanks
Jason.


Have fun

Stanislaw
Slack user from Ulladulla.



OK. I had a deep thought about it all, and came up with a major design
change that *can* include a fan... I previously thought it was impossible
(too hard to explain).
Anyway I got this old "486" CPU fan and heatsink combo (about 400 x 400mm)
that I could attach directly onto the luxeon. Remember my casing is well
ventilated to allow single direction air movement. Would this do it??
I'm
thinking that if this heatsink and fan actually cooled down an old 486
"CPU", why couldn't it cool down a 3W luxeon?
Even better, could I use one of those heatsinks designed specifically for
a
LUXEON (stick-on pin grid) and use my CPU fan on that?

You just have to watch the maximum ratings.If the rating was for a 25 deg.
C sink, then you
can never achieve this without peltier added.

greg


Hi Greg,
So you couldn't tell me, off hand, if my old CPU heatsink and fan might do
the trick? This is where I'm struggling...
I got no idea what my old 50x50mm 486 CPU heatsink's thermal resistance is
:-( It's just a spare part I had lying around with no info, with a small
fan attached.

Peltier? If it comes to that, I'll ditch the luxeon idea altogether... too
much trouble; and power.

Its a good heat sink, but I would lower the drive current fo maximum longevity.
These maximums are at a junction temp of 25 deg. C. These lights can be in
really
harsh environments like busses. With sun and heat, the junction temps could be
really
high. Got to derate. Figure if you could keep the star heat sink at 25 deg. C,
there is another
metal layer before the junction. You have two insulated layers btween the stars
main
sink, and the actual junstion. Placing the star on top of another heatsink just
adds
more differentials.


On my 5 watt Luxeons, the little plate which the Led resides is only 3 mm
in diameter. The metal conducting the heat is only 3 mm dia at the very beginning
and 3 mm long. It ajoins a base plate of about 6 mm in diameter.

greg
.

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