Heatsinks for DIY LED lamps

C

Chuff420

Active Member
I haven't read through this entire thread but I did find Supra's formula for calculating the surface area of a heatsink in order to know how many watts it can dissipate.

Would it be feasible to use a flat aluminium sheet as a heatsink, say 5mm thick, and would the formula still apply? After all, it's just a heatsink with fins measuring at Zero height.

For example , if I had a sheet of 5mm thick aluminium with a width of 800 and a length of 400mm would this work?

Perimeter = (profile width X 2) + (fin height X 2 X # of fins) + (base height * 2) =
Perimeter = (800 * 2) + (0 * 2 * 0) + (5 * 2) = 1610mm = 161cm

Surface Area = Perimeter(cm) * length(cm)
Surface Area = 161 * 40 = 6440 cm²

Thanks
 
ttystikk

ttystikk

Well-Known Member
Chuff420 said:
I haven't read through this entire thread but I did find Supra's formula for calculating the surface area of a heatsink in order to know how many watts it can dissipate.

Would it be feasible to use a flat aluminium sheet as a heatsink, say 5mm thick, and would the formula still apply? After all, it's just a heatsink with fins measuring at Zero height.

For example , if I had a sheet of 5mm thick aluminium with a width of 800 and a length of 400mm would this work?

Perimeter = (profile width X 2) + (fin height X 2 X # of fins) + (base height * 2) =
Perimeter = (800 * 2) + (0 * 2 * 0) + (5 * 2) = 1610mm = 161cm

Surface Area = Perimeter(cm) * length(cm)
Surface Area = 161 * 40 = 6440 cm²

Thanks
Click to expand...
I really doubt it, here's why; how's all that heat going to travel that far across the heat sink? Or to put it another way, the sheet is very likely to be too thin to prevent a high temperature gradient, thereby failing to adequately cool the chip.

The opposite situation is preferable; ALL fins, with only just enough core to hold the chip.
 
dionysus4

dionysus4

Well-Known Member
Chuff420 said:
I haven't read through this entire thread but I did find Supra's formula for calculating the surface area of a heatsink in order to know how many watts it can dissipate.

Would it be feasible to use a flat aluminium sheet as a heatsink, say 5mm thick, and would the formula still apply? After all, it's just a heatsink with fins measuring at Zero height.

For example , if I had a sheet of 5mm thick aluminium with a width of 800 and a length of 400mm would this work?

Perimeter = (profile width X 2) + (fin height X 2 X # of fins) + (base height * 2) =
Perimeter = (800 * 2) + (0 * 2 * 0) + (5 * 2) = 1610mm = 161cm

Surface Area = Perimeter(cm) * length(cm)
Surface Area = 161 * 40 = 6440 cm²

Thanks
Click to expand...
actually yes but not

the bottom half wouldn't be disapating heat as well as the top( i asuume) beacuse the heat couldnt rise away from it
you might be better looking into a C channel for that aproach-ive used those for monos with relative success
 
C

Chuff420

Active Member
Zulunature said:
The Heatsink is 39.6 inches or 1000mm in length.
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Zulunature said:
Thanks for that information as it confirms what I thought. I'm only running 4ft wide so can't see much point. Besides want to run as cool as possible with good spread.
Going to run 4 bars of 4 cobs over 5'6" x 4" area @ 1050ma should produce something worthwhile.
These threads have been a boon for diy building, mouser is out of the HLG185C1400B in aus. but jerry is good to go.

For the Oz lot it cost $175.00
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Hey Zulunature,

I'm interested in the Fastron H42 profile heatsink, and I'm not clear as to what cost $175.

Is that what it cost for a 1000mm length of the Milled H42?

dionysus4 said:
actually yes but not

the bottom half wouldn't be disapating heat as well as the top( i asuume) beacuse the heat couldnt rise away from it
you might be better looking into a C channel for that aproach-ive used those for monos with relative success
Click to expand...
Yep, thought of U Channel as well.

Here's the results:

U Channel.jpg

And this is a sheet of 6.35mm 6061 T651 Mill alloy which is 40mm smaller in both directions than my base of the cabinet just for giggles:

Aluminium Sheet.jpg

Need a Block & Tackle to lift it though.

Active calculations are based on 40cm² & Passive is 120cm².

At this stage CPU coolers are looking like the best option.

Thanks.
 
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Z

Zulunature

Well-Known Member
Chuff420 said:
Hey Zulunature,

I'm interested in the Fastron H42 profile heatsink, and I'm not clear as to what cost $175.

Is that what it cost for a 1000mm length of the Milled H42?
Click to expand...
That's correct and actually the price went up a little in January this year.
So I think it's $185 AUD
 
C

Chuff420

Active Member
SupraSPL said:
You have the formula right, I think it was the fin height that was off. Here is what I get for MF18.151

Perimeter = (125X2) + (56*2*18 ) + (8X2) = 2282mm
Perimeter = 228.2 cm
228.2 * 15.15 fin length = 3457 cm²

Assuming 120cm²/heat W, that heatsink would be good for 29 heat W.

BUT, the distance between the fins is very small and the fin height is relatively tall, so that heatsink might not be considered passive cooling friendly, because of that I would recommend testing the heatsink temp before committing to a large build using that heatsink passively.
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I don't know if anyone has posted this previously, but by transposing Supara's formula we can calculate the required length of any known heatsink given a target HeatW using the following formula. Note that all measurements are in millimetres.

Length = TargetHeatW * cm²/HeatW * 10 / ( ProfileWidth * 2 + FinHeight * 2 * #Fins + BaseHeight * 2 ) * 10

So using the figures from Supras calculation above, and working backwards, we can calculate what length of Conrad M18-151.5 will be required to passively dissipate 29 Heat/W assuming 120 cm²/HeatW.

Supra rounded his final calculation to 29 HeatW. The actual result is:

3457 / 120 = 28.808333333333333333333333333333

So:

Length = 28.80834 * 120 * 10 / ( 125 * 2 + 56 * 2 * 18 + 8 * 2 ) * 10

Length = 151.48995617879053461875547765118 mm

To resolve for Active cooling simply replace the cm²/HeatW in the formula with 40cm².

Hope that helps anyone needing to know what length of heatsink you need for your HeatW requirements.

Enjoy!
 
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C

Chuff420

Active Member
I've been trying to calculate the performance of the Fastron H42 heatsink but I am unsure as to which cm²/HeatW value to use.

I've seen values ranging from 110cm² for HeatsinkUSA's 5.886 profile to 160cm² for Conrad's M18 profile. Specifically for H24, I've seen both 120cm² and 160cm² used in calculations. I understand the M18 having a 160cm² value due to tighter spaced fins, and as such it does not dissipate heat as well as wider spaced fins, but since the H24 is much more like the the 5.886 than the M18, would giving it a value of 160cm² be overly cautious?

True, it's better to err on the side of caution and get a slightly larger heatsink, but the difference between 120cm² and 160cm² equates to a 30% extra length, which not only means it costs 30% more, but the additional length may just make it too big for the cabinet you have.

So, how does one work out the best cm²/HeatW value for a given profile?

Thanks.
 
Z

Zulunature

Well-Known Member
Chuff420 said:
I've been trying to calculate the performance of the Fastron H42 heatsink but I am unsure as to which cm²/HeatW value to use.

I've seen values ranging from 110cm² for HeatsinkUSA's 5.886 profile to 160cm² for Conrad's M18 profile. Specifically for H24, I've seen both 120cm² and 160cm² used in calculations. I understand the M18 having a 160cm² value due to tighter spaced fins, and as such it does not dissipate heat as well as wider spaced fins, but since the H24 is much more like the the 5.886 than the M18, would giving it a value of 160cm² be overly cautious?

True, it's better to err on the side of caution and get a slightly larger heatsink, but the difference between 120cm² and 160cm² equates to a 30% extra length, which not only means it costs 30% more, but the additional length may just make it too big for the cabinet you have.

So, how does one work out the best cm²/HeatW value for a given profile?

Thanks.
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I went overly cautious and have 4 CXB3590 cobs running @1400ma on 1000mm lengths, haven't finished building due to other things in life. I could have gotten away with 700mm and still been passive just felt it would be easier to deal with one lump of heatsink rather than multiples into a frame.
 
frica

frica

Well-Known Member
indianajones said:
I have to give a big thank you to @SupraSPL. With his help i won a contest for agricultural innovation in my state. Because of the contest, I got some sweet CAD designs for free and credit to put towards building aluminum cases for future light models. Thanks man. This is the light I submitted
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That's great to hear, wonderful news.
 
Airwalker16

Airwalker16

Well-Known Member
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