# Rebel heatsink, current



## whitewater (Dec 10, 2007)

I ordered a few LXML-PWC1-0100 from
http://www.led-tech.de/en/High-Power-LEDs-Luxeon/Luxeon-REBEL/Luxeon-REBEL-on-PCB-LT-1120_49_85.html

The rebels are mounted on a aluminum plate. This heatsink is quite different compared to the pcb suggestion in the datasheet. Is this more or less efficient that the heatsink suggested in the datasheet?

I'd like to kit a few with arctic silver epoxy to an aluminum heatsink to make a nice strip lightning. To how many amps could I drive such a system? I saw in the thread about the K2 that someone was driving a rebel to 2 amps, but I have no idea how long the rebel will survive such a load.

Oh, I'd like to drive them the cheap way i.e. have a bunch of em in series with a resistor and powering them off a 230:24V transformator with a bridge rectifier and capacitor. Is that a good idea? What about dimming? Is it possible to use a standard triac dimming system in the 230V line?


Any idea's?


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## Oznog (Dec 11, 2007)

Well that's not a very effective heatsink in itself. The boards without conformal coating and scads of plated throughholes ("Power Pores") are able to dissipate a fair amount of heat. This one needs to be mounted to larger piece of aluminum, something with fins, to get the dissipation.

Driving at high amps is kind of a stunt, for well-cooled systems (lots of fins, very low thermal impedances, no confined casing, in an air conditioned room. And we don't plan on 100,000 lifespans. For an enclosure without exceptional cooling yet you want a long life expectancy 350mA might be a good idea. 700mA if you are good with cooling and monitor the actual temps in the field app.

An unregulated power supply is not a great idea. Transformer secondary voltage changes with line voltage. If we design for minimal voltage drop across the ballast resistor, then current will vary wildly as line voltage changes. If we use fewer series LEDs and drop more voltage across a larger ballast resistor, an impractical amount of heat is generated in the ballast.


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## whitewater (Dec 11, 2007)

Thanks,

I'll get them in a few days. I think it is mounted directly on a aluminum plate, so there is no need for plated pores like in frg4 pcb material. 
About the current, yes I think that you are right about voltage changes on the net, but where I live it is pretty constant. Perhaps 1-2V difference. I'll play around with it and see what is appropriate.
Any idea to what extend the lifetime is affected if the rebels (with a good heatsink) are driven by e.g. 1.4A?


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## Oznog (Dec 11, 2007)

Lifespan depends on die temp. High die temps outside the ratings will ruin a device about the same whether the temp happens in a poorly heatsinked device at 350mA or a somewhat better heatsinked device at higher currents.

I am gonna just say no, your plan to use an unregulated, rectified, and filtered transformer output with just a ballast resistor is a bad plan and puts your very expensive, epoxied-thus-unreplaceable devices at immediate risk. Don't do it. (You did ask for opinions, right?). Actually a buck reg circuit (ZXLD1360,HV9910, etc) isn't all that hard to make, works from a smaller transformer, and make much less heat.


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## boef800 (Dec 13, 2007)

whitewater,
I'm thinking about buying them too.
How is the tint on them?Very cool/bluish?

Alex


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## whitewater (Dec 13, 2007)

Hi Boef800,

I have not received them yet. The company is quite slow is shipment. After a day I emailed them and got an answer that it was shipped. The next day I got another email (from another department) telling me that it was shipped on that day. So it took them 2 days from payment to shipment. That's a bit slow don't you think for a German company?
Now I'm waiting for the GLS guys to deliver it.

So I have no idea what the color is. I let you know when I received them and hooked them up.


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## boef800 (Dec 13, 2007)

Thanks whitewater,
looking forward to hear your impressions when you finally'll get them.
Well yes,if they don't send out an shipping confirmation by themselfs and you have to ask for it,that doesn't sound excactly like what you've come to expect as standard cs behaviour regarding onlineshopping these days.Let's hope they are nevertheless a good company,their rebelboard package looks neat with the isolated top contacts.

Alex


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## whitewater (Dec 13, 2007)

Yes,

I expect from everyone that I paypal a confirmation note that they received it and not an automated thank you note. Also I expect a shipment note with tracking code if applicable. If either of them is not send, I get nervous. And nervous customers are bad for business, starts to ask questions. Its is quite possible that they will never grow to a big company. Anyway I asked them a tracking code by email more than 2 hours ago, no reaction yet. I sell sometimes through ebay. I always send three emails to the customer: thank you email, packing email/ready for shipment and a after posting email with estimated time of arrival. I never had any problem...


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## SemiMan (Dec 14, 2007)

I think you need to be realistic with smaller retailers. Unless they have a fully automated system for generating emails that include shipping details and the like, then they can only "touch" your small order so much and still make a profit.

On the heat sink side, it looks good. I think they could have got more copper under the rebel to improve the transfer into the aluminum core. That said, 0 specifications on thermal performance is not what I would consider ideal.

Semiman


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## whitewater (Dec 14, 2007)

Just received the package. The package was good. Unfortunately no delivery date like tracking code delivered by email. Anyway ordered Monday evening., so 4 days from order to delivery. Is ok, I think although it could be a bit faster.
Products are more important. The rebels are on the alu plate. I'm note sure about the heatsink and if there is copper beneath. I tried one and it looks good. Nice cool [email protected] Great. I Can't measure the lumen output.
I also got a 700mA driver from them. Seems to work. I think it is a linear device -no dc-dc converter (30V max input). Excess input energy is wasted.

I'm off to get some aluminum plate to mount them on.

I keep you posted.


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## boef800 (Dec 14, 2007)

Cool,thanks for the update.
So are they on the very coolish side?Blueish?
Or would you say rather a neutral white for cool-white emitters.
Would like to get neutral/warm ones from them in this package,maybe I'll give them a call asking if they'll get warm ones in.

Alex


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## whitewater (Dec 14, 2007)

The color is not blueish, but it is very hard to tell the exact color. Why don't you get one and test it yourself to see if you like it. It is the same color as the TW0F R2 I got the other day. Check that thread for more info on that led.


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## Stromberg (Dec 15, 2007)

Not really answering to your questions but I bought couple of these ...
http://www.led1.de/shop/product_inf...luxeon-power-leds-luxeon-rebel-star-c-111_221
..and thermal transfer seems to be nearly non-existing. I'd really want to run them at 700mA because at 350mA they are sickly green, but at 700mA leds get burning hot and almost nothing of that heat goes in the heatsink. :scowl:


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## whitewater (Dec 15, 2007)

Perhaps a faulty one?

The problem is that the rebels are not marked and therefore it is impossible to tell what you really got. It sounds that the rebel is not properly heat sinked to the board. Is the board aluminum or frg4?

You can also consider to send them back with a description of the problems. Please report here about the contacts with the seller. We all like to know if they take care of their customers.


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## whitewater (Dec 15, 2007)

Small update:

I glued (with thermal silver epoxy) 5 of the rebel boards to an L profile aluminum strip. The color of the leds are nice cool white and have an output of around 900 lumen. I drive the string of leds with 700mA / 16.9V. That's an average Vf of 3.38V. Average energy consumption per led 2.4W. Temperature of the leds are around 60C when measured with an infrared thermometer.

When I compare the 12W light output with a 12W halogen bulb, it is way brighter.


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## Stromberg (Dec 15, 2007)

whitewater said:


> Perhaps a faulty one?



I bought two of them and both behave identically so I don't think that both are faulty. Board seems to be aluminium. Whitewater, could you do a small test: Turn on the light and let it run say 20 seconds. Then touch the led dome with your finger. How hot do you think that it is?


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## whitewater (Dec 15, 2007)

Hot! 80 deg celcius perhaps?


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## Stromberg (Dec 15, 2007)

So it's normal that the dome of LED can be almost burning hot and still be in the safe limits? :thinking:

I have attached the Rebels to L shaped aluminium strip that is about 22cm long, 4cm wide and about 2mm thick. I'm driving them at 350mA. The strip is getting only very mildly above room temperature, maybe 25ºC. Is it normal or should it go warmer?


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## whitewater (Dec 15, 2007)

Hi,

I've attached 5 rebels (on the alu plate, see first post) attached to a L shape aluminum strip of 100x4x4 cm (3mm thick). The strip does not get warm (700mA through the leds). It sits now against the wall and shines the light along and against the ceiling. Bare emitters are not visible (otherwise you burn your eyes). The light illuminates my desk indirectly (no shadows). Quite nice but not yet enough. I'm waiting for P4's from kaidomain. Also 5 pieces. Have to think about where and how to place them.


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## whitewater (Dec 15, 2007)

Stromberg,

You said that the leds are getting very hot and not the heat sink.
What is not getting warm? The star or the heatsink the star is attached to? What material did you use to connect them?


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## Stromberg (Dec 15, 2007)

whitewater said:


> Stromberg,
> 
> You said that the leds are getting very hot and not the heat sink.
> What is not getting warm? The star or the heatsink the star is attached to? What material did you use to connect them?



Well, at least the heatsink is not getting very warm, only mildly above room temperature. I'm not sure about the star because dome of the led is getting immediately so hot that I've been thinking that it's not good to keep leds running with 700mA. And because of that, I've been running the leds at 350mA which doesn't raise led dome temperature very high.

I've attached the leds with three hex screws and there is thin layer of silicone heat transfer compound between the star and aluminium strip.

Edit:

The light attached to ceiling:


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## whitewater (Dec 15, 2007)

I have a few older luxeons on a star. The stars does get warm, hot and too hot too handle with my fingers when driving with normal currents. That's normal. Did you use a thermal glue like arctic epoxy or something else? That will make a huge difference. I can't see anything in your nice picture.


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## Stromberg (Dec 16, 2007)

whitewater said:


> Did you use a thermal glue like arctic epoxy or something else? That will make a huge difference. I can't see anything in your nice picture.



I used thin layer of silicone heat transfer compound. I have used same stuff with my "old" Prolight 1 watters and it's worked well.


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## Jarzaa (Dec 16, 2007)

Stromberg, did you test the temperetare of the leds by putting your finger on the dome? If so it probably wasn't the led dome that was hot but all the light energy radiating from the led was absorbed to your finger heating it up. Rebels have small dome over the chip so light intensity at its surface is very high.
Check out in this thread and what happened when evan9162 was testing rebels. https://www.candlepowerforums.com/threads/169547&page=4


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## Stromberg (Dec 16, 2007)

Jarzaa said:


> Stromberg, did you test the temperetare of the leds by putting your finger on the dome?
> ...
> Check out in this thread and what happened when evan9162 was testing rebels.



Yes I did! So there is a good chance that the PCB is, in fact, working well but Rebels aren't just emitting "enough" heat @350mA that the heatsink even should be very warm. And it also seems that I made incorrect assumption when I thought that heat from led dome is caused by poor heat conduction. Thanks Jarzaa for your tip of Evans tests.:thumbsup:


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## tonycollinet (Dec 17, 2007)

OK folks

I can feel a new bike light coming on.

Has anyone found any suitable lenses/collimators for these aluminium mounted rebels?


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## whitewater (Feb 13, 2008)

Looks nice! Is it the recommended layout from the manufacturer?

Big hole, does that impair the heat transfer much?

Are you interested in selling these?


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