Rahz
Well-Known Member
Those would be perfect except the center doesn't fully cover the 3590. Mounting issues and possible thermal issues.
New Heatsink Concept
- Thread starter welight
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alesh
Well-Known Member
That's not the answer I was looking for. Basically any heat sink can dissipate 80W. The question is how will it's temperature rise in common ambient temp (25°C).
kony brado
Well-Known Member
Is it true that if a sink have the thermal resistant of 0.59 c/w and you mount a chip at 49w 56% efficient which means 21.56w of heat,the temp rise above ambient will be 21.56 x 0.59 =12.72 celsius above ambient temp?
Is this theoretically correct? Without considering many variables like TIM ,air movement and such?
Iv noticed some companies have data of thermal resistant in comparison to air movment. if have only one number like in this case (0.59) is it true to believe it relate to no air movement?
Is this theoretically correct? Without considering many variables like TIM ,air movement and such?
Iv noticed some companies have data of thermal resistant in comparison to air movment. if have only one number like in this case (0.59) is it true to believe it relate to no air movement?
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Greengenes707
Well-Known Member
He gave the thermal resistance(0.5942 DegC/W). It's all you need to know.
Ex
cxb3590@80w=~45% efficient...so 44w of heat
Ideal temp rise=...50c(desired)-25c(ambients) = 25∆
25(temp rise)÷44w(heat)=.57c/w
subtract the thermal interface ~.05-.1
~0.5c/w is what is need for a 3590 at 80w.
That heatsink should keep temps pretty good even at 80w with a 3590. Anything less efficient will suffer more temp droop.
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robincnn
Well-Known Member
@Greengenes707
I like your 50c. Just your preference I assume.
Anything after 50C gets a little hot to touch and could result in higher temp droops.
I think the industry standard is like 85C
But its too high. I consider max 60C to try and keep case temps under 75C
What I don't know is where is this temp measured. If we know with thermal resistance that heatsink should be 50C. Is this the hotest part of heatsink or average.
I mount thermocouples directly behind or adjacent to cob. Within 10mm from heat source.
I like your 50c. Just your preference I assume.
Anything after 50C gets a little hot to touch and could result in higher temp droops.
I think the industry standard is like 85C
But its too high. I consider max 60C to try and keep case temps under 75C
What I don't know is where is this temp measured. If we know with thermal resistance that heatsink should be 50C. Is this the hotest part of heatsink or average.
I mount thermocouples directly behind or adjacent to cob. Within 10mm from heat source.
kony brado
Well-Known Member
Thanks GG for the math.
( you write TIM ads .5 -1 to thermal resistant but from the math i think u meant .05 -.1 pleas correct me if im wrong)so if i understand than for cxb 3590cd with low quality TIM at 49w the math wold be;
49(w) x .44(heat w) x .69(thermal resistent 0.59+0.1 for the tim)=14.87(celsius temp rise above ambient)
Is this correct?
robincnn
Well-Known Member
Just tested Artic MX4 with vero 29 and got
0.28 C/W between T-hs and T-c at 75 watts passive.
Took measurement at 20C Ta. I will added 5C to my thermocouple temps as I expect grow room to be near 25C.
I have seen c/w for thermal paste goes down the next day as the TIM sets.
Edit:
C/w of heatsinks may be rated 1c/w but it may come out to be 1.5 c/w when heat load is small.
This is because they may rate heatsinks for 85C and you may be using heatsink at 55C. Issue is radiation cooling is temp to power of 4. So radiation cooling is stronger at 85C than 55C. So c/w has non linear relationship with watts
0.28 C/W between T-hs and T-c at 75 watts passive.
Took measurement at 20C Ta. I will added 5C to my thermocouple temps as I expect grow room to be near 25C.
I have seen c/w for thermal paste goes down the next day as the TIM sets.
Edit:
C/w of heatsinks may be rated 1c/w but it may come out to be 1.5 c/w when heat load is small.
This is because they may rate heatsinks for 85C and you may be using heatsink at 55C. Issue is radiation cooling is temp to power of 4. So radiation cooling is stronger at 85C than 55C. So c/w has non linear relationship with watts
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kony brado
Well-Known Member
maybe you will like these
http://www.fischerelektronik.de/web_fischer/en_GB/heatsinks/B03.1/Heatsinks for LEDs/PR/SK590_/index.xhtml
At 20mm thick they are 1.25 c/w more or less,so 10w of heat will get you to 12.5c above ambient .With TIM resistant will get u to13.5c above ambient,so38c above 25 sounds good.
they also got that big inner circle and spaced finns
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Greengenes707
Well-Known Member
Yes, 50c is a preference. And for passive or even enclosed active are awesome numbers. 55c is what I deem my point for under 70w power. That will provide basically affected output over it's life. Over that(75w+) I accept ~60-65c and faster degradation as well as lower performance.
The equation is for projection/estimations and then needs to be real world validated. For me that's with a thermocouple on the Tsp point. Modify the holders to access the Tsp point. Other than being a k-type instead of a soldered on t-type, it's measure by the books.
Welcome. And yes I did mean that. Edited now, thanks.Thanks GG for the math.
so if i understand than for cxb 3590cd with low quality TIM at 49w the math wold be;
49(w) x .44(heat w) x .69(thermal resistent 0.59+0.1 for the tim)=14.87(celsius temp rise above ambient)
Is this correct?
robincnn
Well-Known Member
@Greengenes707 I like the 3590 holder mod for Tsp.
Makes it easy to measure case temps with 3590. Thanks
Makes it easy to measure case temps with 3590. Thanks
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Fastslappy
Well-Known Member
Bump