Today's Message Index:
----------------------
1. 02:37 AM - Re: DIY LED landing light -- Wing skin as heat sink? (John M Tipton)
2. 04:12 AM - Re: DIY LED landing light -- Wing skin as heat sink? (Rob Turk)
3. 07:14 AM - Engine compartment fuse? (C&K)
4. 07:43 AM - Re: DIY LED landing light -- Wing skin as heat sink? (Finn Lassen)
5. 07:55 AM - wiring in conduit (Bob Kuc)
6. 08:08 AM - Re: DIY LED landing light -- Wing skin as heat sink? (Robert L. Nuckolls, III)
7. 08:11 AM - Re: Engine compartment fuse? (Jeff Luckey)
8. 08:12 AM - Re: DIY LED landing light -- Wing skin as heat sink? (Robert L. Nuckolls, III)
9. 08:12 AM - Re: DIY LED landing light -- Wing skin as heat sink? (Robert L. Nuckolls, III)
10. 08:21 AM - Re: Re: ADS-B and Transponder antenna... (Robert L. Nuckolls, III)
11. 08:34 AM - Re: Microair 760 transceivers for sale (Robert L. Nuckolls, III)
12. 08:49 AM - Re: DIY LED landing light -- Wing skin as heat sink? (Robert L. Nuckolls, III)
13. 09:20 AM - Re: DIY LED landing light -- Wing skin as heat sink? (Finn Lassen)
14. 09:29 AM - Re: wiring in conduit (Finn Lassen)
15. 12:09 PM - Re: DIY LED landing light -- Wing skin as heat sink? (Rob Turk)
16. 12:33 PM - Re: Engine compartment fuse? (user9253)
17. 01:16 PM - Re: Engine compartment fuse? (rparigoris)
18. 01:44 PM - Re: wiring in conduit (Robert L. Nuckolls, III)
19. 01:59 PM - Re: Engine compartment fuse? (Robert L. Nuckolls, III)
20. 03:12 PM - Re: DIY LED landing light -- Wing skin as heat sink? (Ernest Christley)
21. 06:18 PM - Re: DIY LED landing light -- Wing skin as heat sink? (Finn Lassen)
Message 1
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
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 =98wig-wag=99 !!!
John
Sent from my iPad
----x--O--x----
> On 2 Nov 2020, at 2:33 am, Ernest Christley <echristley@att.net> wrote:
>
> =EF=BB
> https://electronics.stackexchange.com/questions/294583/does-heatsink-trans
fer-plate-thickness-matter
>
> I think the 4th answer down give the answer. Draw out the path of where y
ou are inputting the heat (back of the module), to where air starts flowing o
ver it.
>
> If it were me, I'd mount it on an 0.80 or 0.90 plate and tape a thermocoup
le on the back. Maybe set a fan in front to simulate the prop turning. If n
ot cool enough, use a thicker plate, or drill more holes.
>
> On Sunday, November 1, 2020, 7:42:33 PM EST, Finn Lassen <finn.usa@gmail.c
om> wrote:
>
>
>> On 11/1/2020 6:37 PM, Robert L. Nuckolls, III wrote:
>>>> 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 junctio
n 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 g
o 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 m
ount 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 watt
s.
> So max thermal resistance of mount plate and mount late to wing skin shoul
d be 56/50 = 1.1W/C. If we use heat sink compound between plate and wing s
kin, we're down to 0.6W/C max thermal resistance of the mount plate. Wow! Ca
n that be right?
> If alum has thermal resistance of 0.2 W/C we need 3 of something. What is t
he something? Thickness vs area? This is where I bog down.
>
> Finn
>
>
> Virus-free. www.avast.com
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
The XM-L2 are Surface mounted. Are you planning to do double-sided PCB
and add via's under each LED, or do you plan on a CNC pattern in
aluminium to allow direct contact to the LED base? The via's have their
own thermal resistance to account for.
Rob
P.S. Cree now have the XM-L3 which tolerate even higher currents and
deliver more lm/watt. Worth a look, I just used some in a strobe config.
> 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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| Subject: | Engine compartment fuse? |
Are there any industry acceptable 30 amp fuses or circuit breakers for
installation on the engine side of the firewall?
Other than a large ANL current limiters I've never noticed fuses or
C/B's in an engine compartment. I am aware of ambient temperature
effects on current limiting devices.
Short story: This is for a 912iS install with the battery and voltage
regulator in the engine compartment and should be something that won't
raise concern from a Transport Canada inspector. At the minimum I'd
like to run the wire between the battery and the voltage regulator
entirely within the engine compartment but it needs 30 amp protection.
thanks
Ken
Message 4
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
Thanks for pointing that out Rob. In my mind I had mixed up the 10W LEDs
I got from mpja.com.
Yes it appears it needs to be soldered to an intermediate PCB. Dang!
Another very significant via in the heat path. LED's mount surface is
4.78x4.478mm, but part of that is the two electrical connectors. I
assume the fiberglass in a PCB has a high heat resistance. Oh, now I
understand your CNC idea. That would give even less mount surface area:
4.78 x 2.78 mm, or so, but much better than via a PCB.
Yes, this thread is getting long. I guess I should have formulated my
question much more clearly to begin with. Although I now have a better
understanding of how the different parts of the heat path add up to a
total heat resistance, the basic question is material thickness of plate
the LED mounts to and the plate's contact area of the wing skin, formula
for. Looking at the site and thread Ernest referred to. I think that
gives me enough data to sensibly calculate mount plate thickness, how it
should taper down and needed contact area with skin.
Finn
On 11/2/2020 7:07 AM, Rob Turk wrote:
>
> The XM-L2 are Surface mounted. Are you planning to do double-sided PCB
> and add via's under each LED, or do you plan on a CNC pattern in
> aluminium to allow direct contact to the LED base? The via's have
> their own thermal resistance to account for.
>
> Rob
>
> P.S. Cree now have the XM-L3 which tolerate even higher currents and
> deliver more lm/watt. Worth a look, I just used some in a strobe config.
>
>> 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
>>
>>
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient&utm_term=icon>
>> Virus-free. www.avast.com
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>
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Message 5
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| Subject: | wiring in conduit |
I have a conduit in the wings of my rv-7a. Wire will be going through it
for wingtip lights. Also in the middle of the right wing I need to add
wire for the roll servo and pitot and aoa wires in the left wing.
Do I cut the tube in the middle to separate to add the wires or do I just
put a hole in the tube to add the wires? Is it OK for the wire to be loose
in the tube? And lastly, what do I put in the ends of the tube to prevent
chafing of the wires? I was thinking either fill ends with hot glue or
shoe glue or even duct sealant.
Thoughts.
Bob Kuc
Message 6
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
>Looking at the Cree XM-L2 with a thermal resistance of 2.5W/C from
>junction to mount surface.
Watts per degree C? Thermal resistance is degreesC/Watt.
Thermal resistance is normally cited as Degrees C (voltage analog)
per Watt (current analog). If the data sheet does indeed call
it 2.5W/C then it's 0.4C/Watt which is rather nominal.
>Add to that a conservative 0.5W/C for heat sink compound . . .
don't you mean 0.5C/W? which added to the assertion
above gives us 0.9C/W . . . a rather nominal and
believable value.
>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.
35C isn't very hot . . . 95F? Anything
higher is detrimental to LED service life?
>The LEDs are "binned" (color and efficiency determined) at 85C.
Okay 85C die and say 25C ambient gives us
a total differential target of 60C.
If the die is pumping out 60W then the
target thermal resistance die-to-ambient
is 60C/60W or 1.0 C/W so your blast cooled sink seems
just adequate.
>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).
okay
>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.
not relevant
>If we have eight 10W LEDs at 30% efficiency, we need to get rid of 56 watts.
okay
>So max thermal resistance of mount plate and mount late to wing skin
>should be 56/50 = 1.1W/C.
or 0.8 degrees C/Watt . . . we're in the same ballpark.
>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.
Thermal resistance of pasted joints are not automatically
0.5C/W . . . a common rule of thumb carried over from
the good-ol-days of TO-3 transistor cases. Thermal resistance
is both area and media dependent. Twice the area drops
thermal resistance by half. Almost anything placed
between two metallic surfaces will drop the thermal
resistance across the joint.
>If aluminum 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.
Thermal resistance becomes a real number only for
specific cases like:
Resistance of a doped interface of TO-3 transistor
to heat sink surface
Resistance of a specific configuration of
heat sink with mass-to-ambient transfer
of heat at a specified airflow.
Resistance of semiconductor junction to it's heat
conducting surface.
The material is irrelevant . . . i.e. aluminum
has no specific thermal resistance until it
becomes part of a fabrication . . . it has
a generalized thermal conductivity value but
doesn't become a component of your thermal
resistance study until after it is fabricated
and then MEASURED or predicted. There
are computer programs not unlike finite element
stress analysis that will do similar studies of
thermal dynamics in an assembly.
https://tinyurl.com/kygh2vo
Here's a skip across the wave tops of a very
complex study
https://tinyurl.com/zsme6t6
Here's a .pdf of a thermal resistance study
I published 4 years ago:
https://tinyurl.com/yxfb9je4
How do you proposed to manage the optics of
this project? Does the natural emission profile
of the LEDS put the light where you want it
most?
I've demonstrated hand held flashlights that
offered sufficient illumination to effect a
graceful arrival with the earth . . . but
they put ALL of their 2 or 3 Watts of output
in the right place.
Headlights on cars generally shine 55W of
incandescent energy or 20W or LED
energy down the road . . . and they'll
light up a road sign a mile away.
Be wary also of too much light where you
don't want it. Incidental light in your
eyes is not conducive to skilled pilotage
1 foot above the runway.
Bob . . .
Message 7
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| Subject: | Re: Engine compartment fuse? |
Ken,
Look at the LittleFuse MIDI line of fuses...
https://www.littelfuse.com/products/fuses/automotive-aftermarket-products/b
olt-down-fuses/midi-boxed.aspx
-Jeff
On Monday, November 2, 2020, 07:26:22 AM PST, C&K <yellowduckduo@gmail.
com> wrote:
Are there any industry acceptable 30 amp fuses or circuit breakers for
installation on the engine side of the firewall?
Other than a large ANL current limiters I've never noticed fuses or
C/B's in an engine compartment.=C2- I am aware of ambient temperature
effects on current limiting devices.
Short story: This is for a 912iS install with the battery and voltage
regulator in the engine compartment and should be something that won't
raise concern from a Transport Canada inspector.=C2- At the minimum I'd
like to run the wire between the battery and the voltage regulator
entirely within the engine compartment but it needs 30 amp protection.
thanks
Ken
-
S -
WIKI -
-
=C2- =C2- =C2- =C2- =C2- -Matt Dralle, List Admin.
Message 8
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| Subject: | Re: DIY LED landing light -- Wing skin as heat |
sink?
At 04:32 AM 11/2/2020, you wrote:
>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 =98wig-wag=99 !!!
Perhaps not . . . during wig-wag operations, energy
to the fan is cut in half which severely reduces
its output but . . . energy dumped by the lamps
is cut in half too. Might not be a big deal. You
need to prototype it and take some MEASUREMENTS.
Bob . . .
Message 9
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| Subject: | Re: DIY LED landing light -- Wing skin as heat |
sink?
At 08:08 PM 11/1/2020, you wrote:
><https://electronics.stackexchange.com/questions/294583/does-heatsink-transfer-plate-thickness-matter>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.
>
Bingo . . . MEASURE on the bench
Bob . . .
Message 10
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| Subject: | Re: ADS-B and Transponder antenna... |
At 06:46 PM 11/1/2020, you wrote:
>
>Here's another useful resource for learning the nanoVNA. It's a
>demo board that you connect to the device in order to learn what the
>test response should look like for various kinds of circuits.
>
>https://preview.tinyurl.com/yxz2hast
I'd seen that offered on Banggood . . . probably
ought to have one.
I do have an earlier version of the NanoVNA that
was barely used used before I acquired the VNATiny
that comes with some sophisticated PC based
management apps . . . but it's NOT self contained.
There are some apps that run in hand held Android
devices . . . I need to explore that further.
I ordered a 4", 1.5G version of the NanoVNA last
night . . . much handier for field and/or quick
look-see tasks. I just may have a very slightly
used NanoVNA for sale pretty soon!
Bob . . .
Message 11
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| Subject: | Re: Microair 760 transceivers for sale |
At 12:08 PM 11/1/2020, you wrote:
>A subscriber to this List has determined
>that a couple of Microair 760 transceivers
>are surplus to his needs. He asked my assistance
>with getting them into new homes.
>
>I've listed them on eBay at auction. All proceeds
>will go to Matt Dralle to support his closet
>full of byte-thrashers that make all this
>good stuff run!
The links are:
https://tinyurl.com/y66qyyn9
https://tinyurl.com/y65akzyc
The second offering shows a user-fab
harness . . . opened it up and discovered
a need for some TLC. Decided to build a new
harness for that one as well.
Bob . . .
Message 12
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
At 06:07 AM 11/2/2020, you wrote:
>The XM-L2 are Surface mounted. Are you planning to do double-sided
>PCB and add via's under each LED, or do you plan on a CNC pattern in
>aluminium to allow direct contact to the LED base? The via's have
>their own thermal resistance to account for.
You bet . . . and they're not going to be 0.5C/W
conductors. You'll need to fasten these critters
down with solder paste and a heat gun. The back
side of the ECB can be solid copper but it's going
to be THIN. Achieving a low resistance thermal
pathway from junction-to-ship's-skin will not be
a trivial task.
Bob . . .
Message 13
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
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@gmail.com> wrote:
>
>
> On 11/1/2020 6:37 PM, Robert L. Nuckolls, III wrote:
>>>> 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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Message 14
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| Subject: | Re: wiring in conduit |
I used the corrugated conduit that Van's sell. I simply made a hole with
a soldering iron (before pulling the wires!)
Actually cut the conduit at the inspection plate to get better access
when riveting the wing skins and installing the bell crank.
Finn
On 11/2/2020 10:48 AM, Bob Kuc wrote:
> I have a conduit in the wings of my rv-7a. Wire will be going
> through it for wingtip lights. Also in the middle of the right wing I
> need to add wire for the roll servo and pitot and aoa wires in the
> left wing.
>
> Do I cut the tube in the middle to separate to add the wires or do I
> just put a hole in the tube to add the wires? Is it OK for the wire to
> be loose in the tube? And lastly, what do I put in the ends of the
> tube to prevent chafing of the wires? I was thinking either fill ends
> with hot glue or shoe glue or even duct sealant.
>
> Thoughts.
>
> Bob Kuc
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
Since you are looking to get the most out of your design, I'd really
recommend you look at the XLamp XM-L3 series. They are identical in size
and shape, but have higher light output for the same current (approx
+20%), they have lower thermal resistance (2.2 vs 2.5 DegC/W), and they
can endure higher max current (5A vs 3A). You may be able to get the
same output using 6 instead of 8 LEDs, which means a lot less losses and
heat to deal with.
Only drawback I have seen is that they are not available in neutral
white, only higher color temperatures.
On 11/2/2020 4:39 PM, Finn Lassen wrote:
>
> Thanks for pointing that out Rob. In my mind I had mixed up the 10W
> LEDs I got from mpja.com.
>
> Yes it appears it needs to be soldered to an intermediate PCB. Dang!
> Another very significant via in the heat path. LED's mount surface is
> 4.78x4.478mm, but part of that is the two electrical connectors. I
> assume the fiberglass in a PCB has a high heat resistance. Oh, now I
> understand your CNC idea. That would give even less mount surface
> area: 4.78 x 2.78 mm, or so, but much better than via a PCB.
>
> Yes, this thread is getting long. I guess I should have formulated my
> question much more clearly to begin with. Although I now have a better
> understanding of how the different parts of the heat path add up to a
> total heat resistance, the basic question is material thickness of
> plate the LED mounts to and the plate's contact area of the wing skin,
> formula for. Looking at the site and thread Ernest referred to. I
> think that gives me enough data to sensibly calculate mount plate
> thickness, how it should taper down and needed contact area with skin.
>
> Finn
>
> On 11/2/2020 7:07 AM, Rob Turk wrote:
>>
>> The XM-L2 are Surface mounted. Are you planning to do double-sided
>> PCB and add via's under each LED, or do you plan on a CNC pattern in
>> aluminium to allow direct contact to the LED base? The via's have
>> their own thermal resistance to account for.
>>
>> Rob
>>
>> P.S. Cree now have the XM-L3 which tolerate even higher currents and
>> deliver more lm/watt. Worth a look, I just used some in a strobe config.
>>
>>
Message 16
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| Subject: | Re: Engine compartment fuse? |
The Rotax 912iS engine comes with a fuse box that is mounted on the
engine side of the firewall. It contains many ATC and Mini fuses.
If Rotax uses them, then so can we.
If a fuse nuisance blows due to ambient temperature, use one size larger.
Could your engine be a 912ULS?
--------
Joe Gores
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499204#499204
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| Subject: | Re: Engine compartment fuse? |
Hi Ken FWIW I just installed a 30 amp MIDI fuse on my Rotax 914. I punched out
the hole of the MIDI to 1/4"and mounted one side to my shunt and the other side
to a 1/4-28 Brass stud so a holder was not needed. McMaster and B&C sells MIDI
holders. Note that MIDI and Maxi fuses are not as fast acting as ATC and MINI.
Maxi fuese are large ATC like fuses. McMaster sells the inline fast on style
holder as well as a more robust clamp style holder. I was on the fence between
MIDI and Maxi. Ron P.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=499206#499206
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| Subject: | Re: wiring in conduit |
At 09:48 AM 11/2/2020, you wrote:
>I have a conduit in the wings of my rv-7a. Wire will be going
>through it for wingtip lights.
>Also in the middle of the right wing I need to add wire for the roll
>servo and pitot and
>aoa wires in the left wing.
>
>Do I cut the tube in the middle to separate to add the wires or do I
>just put a
>hole in the tube to add the wires?
A plastic or conduit I presume. A hole is recommended.
In fact, you can make it quite large to facilitate
pulling the wire into the tube. The conduit is simply
for Z-axis support and routing convenience.
Is it OK for the wire to be loose in the tube?
Yes
And lastly, what do I put in the ends of the tube to prevent chafing
of the wires? I was thinking either fill ends with hot glue or shoe
glue or even duct sealant.
I would put a sleeve of heat shrink over the wire(s)
extending into the conduit 6 inches or so at both
the ends and the mid-tube exit. The things are not
going to 'slide around' in there. Just bevel
the edges of holes/exit points were wires emerge
and buffer the bundles with h-s.
Both wires and conduit are of similar durability/
harness and not antagonistic to each other as long
as there is no forcing . . . and a loose bundle
is not forced. The conduit remains open for future
access.
Goops, goos, glues and other sticky stuffs are to
be applied judiciously and avoided if there are
more elegant choices. We had some really GOOD
goo at Boeing back about 1961 . . . BMS513 . . .
you could retread tires with that stuff. Everybody
hated it for a variety of reasons. Except for
tread sealants on certain plumbing fittings, it was
to be avoided in the TC world.
Bob . . .
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| Subject: | Re: Engine compartment fuse? |
At 10:06 AM 11/2/2020, you wrote:
>Ken,
>
>Look at the LittleFuse MIDI line of fuses...
>
><https://www.littelfuse.com/products/fuses/automotive-aftermarket-products/bolt-down-fuses/midi-boxed.aspx>https://www.littelfuse.com/products/fuses/automotive-aftermarket-products/bolt-down-fuses/midi-boxed.aspx
These things require a mounting block which
might not be a bad thing if it adds a fat-wire
distribution point. But a MAXI holder butt-spliced
into the feeder would work too and much less
fuss. Here's a link to the data sheet
.pdf download
https://tinyurl.com/y3h5wj4o
It can be tied into a wire bundle but has
a hole for mechanical mounting if that
seems more elegant. The holders are
liquid tight.
Both holders and fuses are available at
most carparts emporiums.
Bob . . .
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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
As for reflectors, are they really needed?=C2- The LED has a light patte
rn that puts nearly all of the light forward to begin with.=C2- And LEDs
with a 45 degree pattern are available.=C2- The ones I used from MPJA had
a 160 degree spread, but a chart of the intensity showed very little at th
e ends of that range.
On Monday, November 2, 2020, 12:22:22 PM EST, Finn Lassen <finn.usa@gma
il.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 resis
tance.. 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.=C2- That should expa
nd 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 ==C2- 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, res
ulting in LED junction temp of 85C at 32C ambient, if my calculations are r
ight.
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 g
roves 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 (40x
40mm 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-trans
fer-plate-thickness-matter
I think the 4th answer down give the answer.=C2- Draw out the path of w
here you are inputting the heat (back of the module), to where air starts f
lowing over it.
If it were me, I'd mount it on an 0.80 or 0.90 plate and tape a thermocou
ple on the back.=C2- Maybe set a fan in front to simulate the prop turnin
g.=C2- 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@gm
ail.com> wrote:
On 11/1/2020 6:37 PM, Robert L. Nuckolls, III wrote:
=C2- Are we talking about landing lights?
=C2- Bob . . .
Yes landing lights.
=C2- Okay . . . in the right pew now.
=C2- Is there an engineering data spec sheet available
=C2- for the device(s) you're considering?
=C2- Do you know the thermal resistance from mounting
=C2- surface to LED junction?
=C2- Bob . . .
Looking at the Cree XM-L2 with a thermal resistance of 2.5W/C from junctio
n to mount surface. Add to that a conservative 0.5W/C for heat sink compoun
d 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)=C2- 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 watt
s.
So max thermal resistance of mount plate and mount late to wing skin shoul
d 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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| Subject: | Re: DIY LED landing light -- Wing skin as heat sink? |
On 11/2/2020 6:05 PM, Ernest Christley wrote:
> 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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