Mystery led heat transfer POWER LED
Mystery led heat transfer POWER LED
(OP)
hi everyone
i made a test, i assembled two different type LED (citizen/cree) on the same heat sink, the power of the LED is same (36W) but in the first case i got a temperature (TC) of 70 °c in the second case i got 90 °c....so what the reason of this gap??
thanks
have a good dday
i made a test, i assembled two different type LED (citizen/cree) on the same heat sink, the power of the LED is same (36W) but in the first case i got a temperature (TC) of 70 °c in the second case i got 90 °c....so what the reason of this gap??
thanks
have a good dday





RE: Mystery led heat transfer POWER LED
Also, check the Vf of each.
It might be something we can't see over the internet.
RE: Mystery led heat transfer POWER LED
i double checked, there are the same Vf, they work at 1000mA and have around 35.6 Vf.
you can find anything in internet :)
best
RE: Mystery led heat transfer POWER LED
Swapping things between the two can be very helpful. When the 'fault' moves, you've got it.
RE: Mystery led heat transfer POWER LED
RE: Mystery led heat transfer POWER LED
Efficiency... no two LEDs have the same.
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Mystery led heat transfer POWER LED
Does that mean you found the Vf on the internet or did you measure it in your test?
RE: Mystery led heat transfer POWER LED
Additionally, you say, " i assembled two different type LED (citizen/cree) on the same heat sink," so how did you ensure that the thermal conductances were identical, if at all?
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RE: Mystery led heat transfer POWER LED
If there is a difference in efficiency, and given that they're both being fed with the same 36w of power, wouldn't the more efficient LED be noticeably brighter?
If one LED was noticeably brighter, presumably the OP would have mentioned it. Well, hopefully...
Furthermore, given the low overall efficiency ratio of LEDs in general, any % reduction in waste heat might be a several times larger % increase in light output. Because of the efficiency ratio.
This also ties into the fairly large temperature difference between the reported 90°C and 70°C, which seemed to me to be more than could be explained away by variations in efficiency; assuming that both LEDs are recent products of similar design. And again, given that the OP didn't mention different light output.
Still, you never know... Efficiency might be the answer. Or part of the answer.
Troubleshooting over the internet is often dependent on eliciting the unmentioned details from the OP.
RE: Mystery led heat transfer POWER LED
The cree led is cxb2530 It has an output of 4200 lumen at 1050 mA and the vf misured is 35.6 v.
I used the same thermal pad for both
Also the cri is the same
RE: Mystery led heat transfer POWER LED
How are you "measuring" the Vf? If they both have the same Vf AND If, then they are running the same power, and then only other variable are your thermal pads
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
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RE: Mystery led heat transfer POWER LED
See http://www.cree.com/~/media/Files/Cree/LED%20Compo... It indicates around half the power input into a Cree module generates heat; therefore losing about 18 watts.
If that is being dissipated at 70C into a 20C environment (because why would that be mentioned in the problem statement?) that's a 50C rise vs a 70C rise in the other case. That scales to 25 W or an efficiency difference of 25/36 or 30% efficiency.
RE: Mystery led heat transfer POWER LED
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Mystery led heat transfer POWER LED
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Mystery led heat transfer POWER LED
i made a simulation......after i made thermal test in laboratory with the real Led!
RE: Mystery led heat transfer POWER LED
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Mystery led heat transfer POWER LED
You haven't supplied enough information. Is there an engineer at the company you are working with who can help?
RE: Mystery led heat transfer POWER LED
RE: Mystery led heat transfer POWER LED
This tutorial from Maxim can help:
https://www.maximintegrated.com/en/app-notes/index...