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echristley(at)att.net
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 Posted: Sun Nov 01, 2020 8:12 am Post subject: DIY LED landing light -- Wing skin as heat sink? |
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I got might lights from https://www.mpja.com/20-30-50-Watt-LEDs/products/580/
The drivers are riveted to the wing skin and the LED riveted to a plate of .080" aluminum. They were then riveted to Zenith's mount plate (I have a 601XL). I didn't bother to use any reflectors, as the LEDs tend to concentrate light in one area. One 30W driver wiill handle three 10W LEDs. That will spread the heat out.
Cooling air is provided by a 1/8" hole drilled to stop a crack in the plexiglass cover  If anyone can measure the drag of that 1/8" hole, you're smart enough that I want to be your friend.
On Sunday, November 1, 2020, 10:02:03 AM EST, Finn Lassen <finn.usa(at)gmail.com> wrote:
Sorry, I was looking at the Cree XM-L2. 116 l/w. 116/350 = 33%. At least 5% loss in the driver. So about 31% or 69% heat dissipation. (Not sure about optical efficiency. I guess that's heat in the lens and reflector.)
So thickness of mount plate should not be a factor? A 10W LED I have has a 1.6mm thick metal base, but I guess that's needed to screw it down to heat sink with proper contact (minimal heat sink compound thickness).
Alum: 205 W/mK or 0.205W/C. But, but ... is cross area not a factor? Trying to compare it to electrical resistance in a wire. The higher the cross area -- the less resistance.
Trying to wrap my head around the transition from flat contact area under the LED chip to the heat sink plate as it expands out in area. Seems mounting it to an infinite piece of alum foil would not be the same as mounting it to 10x10" 0.063" thick alum plate ...
Finn
On 11/1/2020 9:25 AM, Robert L. Nuckolls, III wrote:
| Quote: | | Quote: | | Let's say we use a 100W LED (~13,000 lumens). We'd have to remove 70 to 80W of heat from the LED. |
AND the associated electronics.
See attached:
Bob . . . |
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echristley(at)att.net
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| Posted: Sun Nov 01, 2020 6:16 pm Post subject: DIY LED landing light -- Wing skin as heat sink? |
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https://electronics.stackexchange.com/questions/294583/does-heatsink-transfer-plate-thickness-matter
I think the 4th answer down give the answer. Draw out the path of where you are inputting the heat (back of the module), to where air starts flowing over it.
If it were me, I'd mount it on an 0.80 or 0.90 plate and tape a thermocouple on the back. Maybe set a fan in front to simulate the prop turning. If not cool enough, use a thicker plate, or drill more holes.
On Sunday, November 1, 2020, 7:42:33 PM EST, Finn Lassen <finn.usa(at)gmail.com> wrote:
On 11/1/2020 6:37 PM, Robert L. Nuckolls, III wrote:
| Quote: | | Quote: | | Quote: | Are we talking about landing lights?
Bob . . . |
Yes landing lights.
|
Okay . . . in the right pew now.
Is there an engineering data spec sheet available
for the device(s) you're considering?
Do you know the thermal resistance from mounting
surface to LED junction?
Bob . . . |
Looking at the Cree XM-L2 with a thermal resistance of 2.5W/C from junction to mount surface. Add to that a conservative 0.5W/C for heat sink compound and we get 3W/C.
Max die temp is 150C. But unlimited life is 35C. It appears that when you go above 35C you start reducing life of the LED.
The LEDs are "binned" (color and efficiency determined) at 85C.
So lets set die temp of 85C as the design goal.
With built-in temp limiting, I think we can probably consider wing skin to air thermal resistance as 0W/C (air flowing over the skin in flight).
Consider 32C ambient we get 85 -3 -32 = 50 allowed temp difference from mount plate to skin.
Each LED has a mount surface of about 20x20mm.
If we have eight 10W LEDs at 30% efficiency, we need to get rid of 56 watts.
So max thermal resistance of mount plate and mount late to wing skin should be 56/50 = 1.1W/C. If we use heat sink compound between plate and wing skin, we're down to 0.6W/C max thermal resistance of the mount plate. Wow! Can that be right?
If alum has thermal resistance of 0.2 W/C we need 3 of something. What is the something? Thickness vs area? This is where I bog down.
Finn
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john(at)tipton.me.uk
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| Posted: Mon Nov 02, 2020 2:37 am Post subject: DIY LED landing light -- Wing skin as heat sink? |
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I though about mounting a computer (CPU) fan over the fins to give a flow of air, but this idea falls down if your lights ‘wig-wag’ !!!
John
Sent from my iPad
----x--O--x----
| Quote: | On 2 Nov 2020, at 2:33 am, Ernest Christley <echristley(at)att.net> wrote:
https://electronics.stackexchange.com/questions/294583/does-heatsink-transfer-plate-thickness-matter
I think the 4th answer down give the answer. Draw out the path of where you are inputting the heat (back of the module), to where air starts flowing over it.
If it were me, I'd mount it on an 0.80 or 0.90 plate and tape a thermocouple on the back. Maybe set a fan in front to simulate the prop turning. If not cool enough, use a thicker plate, or drill more holes.
On Sunday, November 1, 2020, 7:42:33 PM EST, Finn Lassen <finn.usa(at)gmail.com> wrote:
On 11/1/2020 6:37 PM, Robert L. Nuckolls, III wrote:
| Quote: | | Quote: | | Quote: | Are we talking about landing lights?
Bob . . . |
Yes landing lights.
|
Okay . . . in the right pew now.
Is there an engineering data spec sheet available
for the device(s) you're considering?
Do you know the thermal resistance from mounting
surface to LED junction?
Bob . . . |
Looking at the Cree XM-L2 with a thermal resistance of 2.5W/C from junction to mount surface. Add to that a conservative 0.5W/C for heat sink compound and we get 3W/C.
Max die temp is 150C. But unlimited life is 35C. It appears that when you go above 35C you start reducing life of the LED.
The LEDs are "binned" (color and efficiency determined) at 85C.
So lets set die temp of 85C as the design goal.
With built-in temp limiting, I think we can probably consider wing skin to air thermal resistance as 0W/C (air flowing over the skin in flight).
Consider 32C ambient we get 85 -3 -32 = 50 allowed temp difference from mount plate to skin.
Each LED has a mount surface of about 20x20mm.
If we have eight 10W LEDs at 30% efficiency, we need to get rid of 56 watts.
So max thermal resistance of mount plate and mount late to wing skin should be 56/50 = 1.1W/C. If we use heat sink compound between plate and wing skin, we're down to 0.6W/C max thermal resistance of the mount plate. Wow! Can that be right?
If alum has thermal resistance of 0.2 W/C we need 3 of something. What is the something? Thickness vs area? This is where I bog down.
Finn
Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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echristley(at)att.net
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| Posted: Mon Nov 02, 2020 3:12 pm Post subject: DIY LED landing light -- Wing skin as heat sink? |
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As for reflectors, are they really needed? The LED has a light pattern that puts nearly all of the light forward to begin with. And LEDs with a 45 degree pattern are available. The ones I used from MPJA had a 160 degree spread, but a chart of the intensity showed very little at the ends of that range.
On Monday, November 2, 2020, 12:22:22 PM EST, Finn Lassen <finn.usa(at)gmail.com> wrote:
Thank you Ernest. This sentence "Copper Has a thermal conductivity of 401 W/(m K)" did it.
I thought the "m" stood for "milli" when I first Googled alum thermal resistance.. It's meters, think. In other words thickness.
So alum is 205 W/Meter K or W/Meter C.
Area apparently nulls out. Whether applying 1 W heat to 1 square meter or to 1 square mm it will still drop 205C per meter thickness. Right?
Intuitively the mount plate has to be at least as thick as half the widest edge of the LED base. Then can taper down as the area spreads out.
The Cree XM-L2 has an (inner) 4.78x2.78mm base. so 4.78 * 0.5 / 25.4 = 0.094" So your 0.09 plate thickness is close.
Let's assume a 0.035 sq in LED base on a 0.1" plate. That should expand out to about 0.14 sq in contact area with 0.025" skin. (0.1 /0.025)
On my RV-4 there would be about 1.5" or about 0.04m from LED to wing skins. Two of those, 0.02m. 0.02 x 205 = 4C/W.
Add to that 2.5 for LED junction to mount base. 0.5 mount base to plate and 0.5 mount base to wing skin and we get 7.5C/W.
7 W would result in a temp drop of 53 C from LED junction to wing skin, resulting in LED junction temp of 85C at 32C ambient, if my calculations are right.
With 8 LEDs the mount plate to wing contact should be 1.12 sq in. Easy with two 1/2" flanges x 2 to 3".
To implement this I would probably mount the LEDs on a 1/8" alum bar with groves milled for electical connectors. 2 rows of 4 LEDs. Adding reflectors is a whole other problem.
Actually the 100W 45mil Bridgelux LED chip might make it a lot simpler (40x40mm mount area). Sure the mount plate would be a lot thicker in the center ...
https://www.stratusleds.com/module Finn On 11/1/2020 9:08 PM, Ernest Christley wrote:
https://electronics.stackexchange.com/questions/294583/does-heatsink-transfer-plate-thickness-matter
I think the 4th answer down give the answer. Draw out the path of where you are inputting the heat (back of the module), to where air starts flowing over it.
If it were me, I'd mount it on an 0.80 or 0.90 plate and tape a thermocouple on the back. Maybe set a fan in front to simulate the prop turning. If not cool enough, use a thicker plate, or drill more holes.
On Sunday, November 1, 2020, 7:42:33 PM EST, Finn Lassen <finn.usa(at)gmail.com> (finn.usa(at)gmail.com) wrote:
On 11/1/2020 6:37 PM, Robert L. Nuckolls, III wrote: | Quote: | | Quote: | | Quote: | | Are we talking about landing lights? Bob . . . |
|
| Quote: | | Yes landing lights. |
Okay . . . in the right pew now. Is there an engineering data spec sheet available for the device(s) you're considering? Do you know the thermal resistance from mounting surface to LED junction?
Bob . . . |
Looking at the Cree XM-L2 with a thermal resistance of 2.5W/C from junction to mount surface. Add to that a conservative 0.5W/C for heat sink compound and we get 3W/C. Max die temp is 150C. But unlimited life is 35C. It appears that when you go above 35C you start reducing life of the LED. The LEDs are "binned" (color and efficiency determined) at 85C. So lets set die temp of 85C as the design goal. With built-in temp limiting, I think we can probably consider wing skin to air thermal resistance as 0W/C (air flowing over the skin in flight). Consider 32C ambient we get 85 -3 -32 = 50 allowed temp difference from mount plate to skin. Each LED has a mount surface of about 20x20mm. If we have eight 10W LEDs at 30% efficiency, we need to get rid of 56 watts. So max thermal resistance of mount plate and mount late to wing skin should be 56/50 = 1.1W/C. If we use heat sink compound between plate and wing skin, we're down to 0.6W/C max thermal resistance of the mount plate. Wow! Can that be right? If alum has thermal resistance of 0.2 W/C we need 3 of something. What is the something? Thickness vs area? This is where I bog down. Finn Virus-free. www.avast.com [url=#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2] [/url]
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echristley(at)att.net
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| Posted: Tue Nov 03, 2020 5:56 am Post subject: DIY LED landing light -- Wing skin as heat sink? |
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Good gawd! Those lights are ridiculous bright.
Here's a question: If I strap enough of these to my wings, will it effectively nullify the day only restriction on my operating limitations?
On Monday, November 2, 2020, 9:19:22 PM EST, Finn Lassen <finn.usa(at)gmail.com> wrote:
On 11/2/2020 6:05 PM, Ernest Christley wrote:
| Quote: | As for reflectors, are they really needed? The LED has a light pattern that puts nearly all of the light forward to begin with. And LEDs with a 45 degree pattern are available. The ones I used from MPJA had a 160 degree spread, but a chart of the intensity showed very little at the ends of that range.
|
Well, my goal is to light up at least 1,000 feet of the runway, preferably 3,000.
Charlie referred to a landing light with a 3 degree beam width.
I guess with a strong enough LED (like 100W or 9,000 lumens) the bean width may not be all that important.
For the reflector for the https://www.stratusleds.com/module is "the beam is around 15 degrees with a soft falloff".
But definitely a good point.
Finn
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