Luxeon Star heatsink temperature

[Bart]

I have two amber luxeon star/c modules with TO-220 type heatsinks. I am runing 2.89v @ 300mA and the heatsinks have gotten up to 123.4 degrees F, and are now just hovering around 121.3 degrees F. I just want to make sure that this is OK. This is with ambient temperature of 72 to 75 degrees. What I want to do is use these for my side-markers on my car. Since there's no room for heatsinks, I plan on mounting the modules directly onto my car chassis and putting the lens over the top. Would the chassis of the car make a good heatsink?

 

[Silviron]

You are fine if that temperature is indeed in Farenheit.- Thats only about 51 C and well within the limits of a LS.

I would think a car body would be a decent heat sink, unless you are installing very close to headers or a catalytic converter.

 

[Bart]

Definitely not close to any heat source on the car, except for the sun maybe... but the car is silver so it will reflect a lot more than absorb. Thanx for your input... I just wasn't sure if it was normal for them to get this hot. They still work fine, but I'm use to LED's generating little heat. I'm very impressed with these, just one underdriven luxeon is a little bit brighter than a standard 5 watt side marker light.

 

[The_LED_Museum]

It would probably be OK, but don't be Scrooge with the heat sink compound.

 

[vcal]

Excellent advice, and especially that part about not mounting the Luxeon right next to the catalytic converter.

p.s.-all kidding aside,-does anybody know if the operating voltage of those Luxeon Amber & Red Modules is less than the White or Blue-(for example)?

 

[PeLu]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by videocal:
anybody know if the operating voltage of those Luxeon Amber & Red Modules is less than the White or Blue-(for example)?<HR></BLOCKQUOTE>

You mean probably the maximum working temp? Usually they are the same, but the amber suffers much more from a hot die than the others. Look at the graphs in the spec sheet. Keeping the amber as cool as possible makes high efficiency.

And most car's bodies do not make a very good heatsink: the steel is pretty thin and much less heat conducting as aluminium. Of course its better than no heatsink at all.

 

[Silviron]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by videocal:
...does anybody know if the operating voltage of those Luxeon Amber & Red Modules is less than the White or Blue-(for example)?<HR></BLOCKQUOTE>

Yes, the operating voltage of the amber, red and red-orange LEDS is less than the whites, cyans and greens- listed in order of Minimum, Typical and Maximum here are the operating voltages of the colors according th the LumiLeds data sheet:

RED & AMBER (low dome, LXHL-ND98, NL98) 2.25V, 2.85V, 3.27V

RED , AMBER and RED/ORANGE (High Dome, ND94, NH94 NL94) : 2.31V, 2.95V, 3.39V

Compared to 2.55V, 3.42V, and 3.99V for the low dome whites & blues etc.

 

[Silviron]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by PeLu:
...car's bodies do not make a very good heatsink: the steel is pretty thin and much less heat conducting as aluminium.<HR></BLOCKQUOTE>

There is more to heat sinking efficiency than just the thermal conductivity of the metal- surface area and airflow are also as important.

There is no doubt in my mind that the surface area of a car body is more than sufficient to make up for the lower thermal conductivity of steel compared aluminum or copper. And when in motion, airflow should be quite sufficient too.

Of course if you have a fiberglass body (or titanium body

) then you do have a problem, since neither one of them are good thermal conductors....

 

[Bart]

it's steel... the only non-metal body parts are the bumpers. It is hollow underneath so there's at least some air flowing on both sides of the metal. with that said, I have an idea. I can use the heatsinks I have and mount them on the other side of the quarterpanel on my car right where the LED is. I'm sure that with both the chassis and the heat sink, it should definitely stay cool enough.

 

[vcal]

Silviron,
Thanks for that soon-to-be useful info, as I'm now itching to construct a powerfulreally small pocket light using the Hi-Dome amber Luxeon:O

p.s.-not at all sure about how to dissipate the associated heat in something that small though..
-Am I correct in assuming that the Luxeon module operating out in the open, by itself, and with proper voltage, will not overheat?

 

[Silviron]

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

-Am I correct in assuming that the Luxeon module operating out in the open, by itself, and with proper voltage, will not overheat?<HR></BLOCKQUOTE>

I'm always a bit shocked at how hot these darn things run, even at their "typical" voltage". I have had to heat sink and ventilate all of my conversions with them so far; {all in non-metallic bodies (still haven't done a Maglight conversion yet

I think that in a metal body you may not have to ventillate with PROPER heat sinking... )}.

Anyway, you SHOULD be ok with the module in open air with the voltage at no more than "Typical" (as long as the ambient air temp stays under 95-100F although I'm just guessing about this part).

I just started a 2 D cell test on an amber LS - In open air (80 F) with moderate air circulation, no heat sink it is running at about 72 C- too hot to hold without gritting your teeth

, but within the limits set by the manufacturer. (75C operating temp with optics, {105C PCB temp})

However, if you cut off the air flow the temp goes way over 80C (that's where I quit testing). NOT good in my opinion.

On one of those neat round heatsinks that I found at All Electronics (I posted the URL to them on an earlier thread), the LS stays under 57C in open circulating 80F (27C) air and about 65C with no circulation.

These measurements were taken with a 2.98V "no load" supply, with the LS drawing 224mA @ 2.74V

So, bottom line in my opinion: Heatsink whenever possible, have good airflow around the aluminum base of the module unless you have a GREAT heatsink that is able to transfer heat to the "outside".

This is with "constant" power. Intermittant use or Pulsed power supplies will change that - I don't know how significantly since I haven't personally done any work with them yet.

 

[Bart]

You would think that Luxeon.com would have some article dealing with heatsinks. Lumileds.com has suggested application articles for their snapleds and talk about temperature and such. Either way... the way I think about it, the cooler you keep the LED, the longer it will last and the brighter you can make it.