Re: Heatsinking a 3W Luxeon


"GregS" <szekeres@xxxxxxxx> wrote in message
news:e8bbpc$r8l$3@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
In article <44a92152$1_1@xxxxxxxxxxxxxxxxxxx>, "Jason S"
<jst3712@xxxxxxxxxxxxxx> wrote:

"GregS" <szekeres@xxxxxxxx> wrote in message
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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.

greg



I can assure you my light won't be operating in ambient temperatures beyond
25 deg C ... and definately not in a hot car or bus! lol.

Sorry, I'm full of questions as usual! haha ........

Because I am still in the 'design' stage, I am thinking of slightly lowering
the drive current anyway, down to 800/900mA? I suppose this would relieve a
bit of pressure already right? I purchased a '1000mA BuckPuck' that has
an inbuilt pot to adjust the current to a lower setting if required... still
awaiting delivery of it.
About the metal layers, I don't know what you're talking about because I
don't have one to look at (yet), but I will question your comment once I get
my hands on one.
Would you recommend joining the star's heatsink to my larger 'foreign'
heatsink using '25% silver thermal compound'? I read that its heat transfer
is better than the normal stuff.

Jason.



.

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