Luxeon Star run with no additional heatsink?

[MrAl]

Hello there,

1 watt Lux stars...

I am wondering if any people run their Lux Stars with just the
heat sink that comes mounted to the emitter?
I ran mine at only 270ma and gee it seemed to get pretty hot.

I run another 1 watter in a light that drives it about 300ma or so,
but that Lux has the old style square heat sink which is a bit
bigger.

So the question is... do you run your 1 watt Luxeons with only
the heat sink that it comes mounted to and if so what current
do you run at?

Thanks.

.

 

[wasBlinded]

You can run a Lux1 at spec with no other heat sinking, and it will do OK. As you know, it will get very hot, and you will have some lumen loss and probably inconsequential (depending on your application) ultimate loss of longevity if you do it.

There are some inexpensive lights that do this, like the Sam's Club Element.

If you are interested in looking into this further, this application brief will guide you:
LUXEON Thermal Design Guide

 

[MrAl]

Hello again,

Thanks much for the link...that is helpful.

I did a few calculations and now i see why these Lux's get so hot.
The heat sink is only approx 0.3 square inches, whereas the older
type heat sinks were 1 square inches. This is a BIG difference.
The temperature rise on the new Lux is much greater than with the
older Lux. This means i'll need a heat sink, especially since i'd like to
go up to the full 350ma with this.

Now the only remaining question...

Has anyone ever mounted a Luxeon Star to a heatsink with 'normal'
epoxy? That is, not the special epoxy you buy for this kind of thing.
I had some epoxy that is rated for fairly high temperature but
it's not specifically made for heatsinks, and i'd like to use it, if possible.

 

[Meduza]

That epoxy would propably not be so termally conductive and would ruin the idea of having a heatsink due to that it protects from heat transfer.

Artic Alumina Epoxy is really worth it!

 

[MoonRise]

AFAIK, regular epoxy or adhesives are not very good at heat transfer.

Just get some Arctic thermal epoxy. Over in the Dealer section, you can order it from PhotonFanatic or from other sources as well.

Also remember that thermal epoxy/adhesive is better than regular adhesive at thermal transfer, but it still is waaaaaay worse than aluminum or just about any other commonly used metal at thermal conductivity. So try to keep the adhesive layer thin-thin-thin, as in 1-2 thousandths (0.001-0.002) inch thick. You can check some of the specs on ArcticSilver's web site.

 

[IsaacHayes]

The old square heatsinks cameon the star-o and the luxeon-c (IIRC) low domes.

 

[Illum]

thats how this light runs

http://www.flashlightreviews.com/reviews/dorcy_3wlantern.htm

the 3W is sitting on A PLASTIC BASE BEHIND A PLASTIC REFLECTOR....poor emitter... [sniff], bound to cook itself to death

 

[wasBlinded]

You can also buy some alumina powder from the Sandwich Shoppe and mix that into the epoxy of your choice. This will make a pretty good thermal epoxy, and a lot cheaper than the branded stuff if you need very much of it.

 

[wasBlinded]

One other thing, the Luxeon Star MCPCB itself is more than .3 square inches of heat sink, as Lumileds figures it. You have to count the top and side surfaces of the Star in the calculation too. They say it is 1 square inch, but it wouldn't surprise me if they were rounding that figure up a little bit

 

[chimo]

Al, since you are only running at 1 watt, you could probably get away with normal epoxy (perhaps one of the "steel" types).

However, a better solution would be to use thermal paste and screw the star down, or thermal paste under the star with a small ring of epoxy around the outside.

Paul

 

[MrAl]

Hi again,

Thanks for all the ideas and suggestions.

I didnt want to wait for a shipment to arrive (thermal epoxy) so i
went ahead and decided to test the PC-11 epoxy for this application
I would bet this is the worst possible epoxy to use for thermal apps
because this stuff contains a filler that makes it much thicker than
ordinary epoxy (also not good) but all the other epoxy i had wasnt
rated for any temperature so i think it would just melt off.

So anyway, i applied the epoxy to an aluminum angle and stuck on the
two Luxeon stars and using four very small clamps clamped both of
them down securely. A few hours later i applied some power so as to
heat up the heatsink a little and get the epoxy to cure faster (it's an
overnight cure type). I felt the heatsink and it did get warm, but
i didnt want to keep the heat going for too long... just enough to boost
the cure rate.
So now i have to wait till tomorrow to test this out. I intend to apply
full power and see if the little disk of the LS heats up the way it did before.
If it doesnt, im in luck. If it does, i guess im back to square uno.

I'd like to eventually get some of that Artic stuff, but i just didnt feel
like waiting for it to get here in the mail
Next time...

I have some thermal paste laying around somewhere too, but didnt feel
like drilling any holes tonight either Good idea though.

Oh yeah, BTW, i consider that little aluminum disk on the LS to be only
about 0.3 inches square because i dont count the top, and i certainly
dont count the sides. The reason i dont count the top is because it
is covered with mostly non-conductive items like the emitter plus some
sort of circuit board. Believe me, the way this thing was heating up is
really was like it only had 0.3 sq in surface area too! You could smell that
"something electronic is frying out" kind of smell if you put your nose
just above it after it had been run for a few minutes.

 

[wasBlinded]

I think you are going to be just fine with your non-thermal epoxy. It won't take very much extra heat transfer to cool that little star down quite a bit.

 

[IsaacHayes]

I forget the current specs a lux1 could run with just the bare star. I think it was like 150ma or something? A lot less than 350ma I know that.

 

[wasBlinded]

I forget the current specs a lux1 could run with just the bare star. I think it was like 150ma or something? A lot less than 350ma I know that.

Lumileds specifically states that the Luxeon Star can be operated without a heatsink at 25 deg C ambient, and although they don't specify the current I'm pretty sure they are talking about at least the 350 mA spec of the LuxI.

Keep in mind that the specs allow for a board (star) temperature of up to 105 deg C. Thats pretty hot, and not something you or I would want to see with our flashlights!

 

[MrAl]

Hi again,

WasBlinded:
Yes, i think you are right in that the little extra cooling even with the
'normal' epoxy will help enough to make it run ok.
They allow up to 105 deg C ? Well, that's good. But i have a feeling
that statement they make about running without a heatsink is about
the type with the square heat sink, not the hex one. I could be wrong,
but i dont want to bet two Luxeon 1 watters that they dont blow out
due to overheat, or even if they dont blow out, i dont want to see them
get any serious life reduction due to running way too hot or even
running at the spec of 105 deg C.

So far so good...this morning i connected the two luxeons to a 170ma
source which gets them a little warm, to help finish off the epoxy curing
process. I'll leave it run like that for a few hours, then test with 270ma.
I wont be able to test at the full 350ma until i get the correct resistor
value, but even at 270ma the stars would get super hot, so i consider
this a good test too.
With 170ma, the heat sink gets just a little warm, so i know some heat
is being transferred for sure.
I'll post again later today sometime with results of the test at 270ma.
I put that epoxy on in a super super thin layer (being sure the surfaces
got 'wet' of course), so i expect this to work to at least some degree.

I can feel the top of the Lux and it's feeling about the same temperature
as the heat sink...which is much cooler than before at 170ma, so this
must be working...but more later at the higher current.

I wonder now what the smallest quantity of that Artic epoxy stuff you
can purchase online is? I dont want to buy it and then have it sitting
around for years after only one use.

 

[MoonRise]

Al,

The smallest quantity of Arctic Alumina epoxy is 2.5 grams AFAIK, which is two small tubes. Volume is probably around one ounce, give or take.

Go to the dealers section here on CPF, find Photonfanatic's sales thread at http://candlepowerforums.com/vb/showthread.php?t=85330 , and order some for $6.75. Or order some Arctic Silver thermal epoxy in the 3.5 gram size (same volume roughly as the Alumina, but silver is heavier than aluminum) for $14.25. Order some LEDs, reflectors, etc as well. Just a satisfied customer.

IIRC correctly, the SandwichShoppe has the products as well, if you want another source or are buying other pieces.

 

[PEU]

Al, PM me your address and I purchase some artic alumina for you in the sandwich shoppe


Pablo

 

[MrAl]

Hello again,

Moonrise: Thanks for the link. Where are the products listed for the
sandwich shoppe? I would like to view a listing of all available products.

PEU:
Thanks once again! I dont want you to have to do that however.
BTW i couldnt get a pic to display on the EE web site Permissions again?
Thanks again so much for your generous offer.

 

[wasBlinded]

If you are looking for the "Thermal Management" products at the Sandwich Shoppe, this link will do it:

http://theledguy.chainreactionweb.com/index.php?cPath=48_39

The alumina powder to make your own thermal epoxy is pretty cheap!

 

[PEU]

Hello again,
PEU:
Thanks once again! I dont want you to have to do that however.
BTW i couldnt get a pic to display on the EE web site Permissions again?
Thanks again so much for your generous offer.

I just checked mral.peu.net and its working OK, just in case I sent you a PM with the login data.

Regarding artic alumina, my offer is firm, as long as you still want it , you helped me and the whole forum so many times that I feel happy just by helping you with this little gift

cheers


Pablo