Nav Lights using Luxeon LEDs

Recently I designed and built a nav light system for my Europa aircraft
using the Luxeon LEDs with great results.

I also measured the radiation pattern (after fitting the LEDs to the
aircraft) and compared it to the FAR specs. It exceeds the requirements
by 3-5 times, and draw only 2 Amps total. It is bright enough to almost
use as a landing light.

Actually, I am surprised that most manufacturers do not provide a
measured radiation pattern. They just say that it complies with the
FAR. Well, meeting the specs is not the same as exceeding it. Since
LEDs lose power with age, this could be an important consideration.

Just in case someone might find this useful, I wrote it up as an
article:
http://www.sarangan.org/aviation/eur...tip-Lights.pdf

Let me know what you think.

I think you are a great guy.

Andrew Sarangan wrote:
Recently I designed and built a nav light system for my Europa aircraft
using the Luxeon LEDs with great results.

I also measured the radiation pattern (after fitting the LEDs to the
aircraft) and compared it to the FAR specs. It exceeds the requirements
by 3-5 times, and draw only 2 Amps total. It is bright enough to almost
use as a landing light.

Actually, I am surprised that most manufacturers do not provide a
measured radiation pattern. They just say that it complies with the
FAR. Well, meeting the specs is not the same as exceeding it. Since
LEDs lose power with age, this could be an important consideration.

Just in case someone might find this useful, I wrote it up as an
article:
http://www.sarangan.org/aviation/eur...tip-Lights.pdf

Let me know what you think.



--
J Kimmel

www.metalinnovations.com

"Cuius testiculos habes, habeas cardia et cerebellum." - When you have
their full attention in your grip, their hearts and minds will follow.

"Andrew Sarangan" wrote in message
oups.com...
Recently I designed and built a nav light system for my Europa aircraft
using the Luxeon LEDs with great results.

I also measured the radiation pattern (after fitting the LEDs to the
aircraft) and compared it to the FAR specs. It exceeds the requirements
by 3-5 times, and draw only 2 Amps total. It is bright enough to almost
use as a landing light.


Splendit! Great work, Andrew!

One note... When looking at the schematics it appears you're building two
current sources. Without digging too deep it seems the serial resistors are
switched between the two drawings (0.69 Ohm for 1400mA, 1.3 Ohm for 700mA)??

Rob

Actually, those are current sensing resistors, not current limiting.
The voltage across the resistor is compared with a fixed reference
voltage, and it is the FET which limits the current. So, a higher
resistor does not necessarily mean lower current.

Rob Turk wrote:
"Andrew Sarangan" wrote in message
oups.com...
Recently I designed and built a nav light system for my Europa aircraft
using the Luxeon LEDs with great results.

I also measured the radiation pattern (after fitting the LEDs to the
aircraft) and compared it to the FAR specs. It exceeds the requirements
by 3-5 times, and draw only 2 Amps total. It is bright enough to almost
use as a landing light.


Splendit! Great work, Andrew!

One note... When looking at the schematics it appears you're building two
current sources. Without digging too deep it seems the serial resistors are
switched between the two drawings (0.69 Ohm for 1400mA, 1.3 Ohm for 700mA)??

Rob

"Andrew Sarangan" wrote in message
oups.com...
Actually, those are current sensing resistors, not current limiting.
The voltage across the resistor is compared with a fixed reference
voltage, and it is the FET which limits the current. So, a higher
resistor does not necessarily mean lower current.


Ahh yes. I saw the current sensing resistors but I overlooked the resistor
values for the divider that creates the fixed reference. I'm still wondering
about a few things though, hope you can elaborate a bit.

- You have the fuse placed in the ground wire. However, the largest
'touchable' area on your PCB and heatsinks are all attached to the area
behind the fuse. A simple protruding screw or rivet would be enough to turn
the circuit into an unfused system. Why not fuse the 12V line?

- The LM7805 really likes having a small decoupling capacitor at it's output
to prevent oscillation (and even self-destrucion on cheap non-brand 7805's).
How about adding 100nF between the 5V output and ground?

- The current sense resistor in the 1400mA version will dissipate about (1.4
x 1.4 x 1.3) 2.6W, so a 3W resistor is OK. The 700mA version would only
dissipate (0.7 x 0.7 x 0.69) about 0.36 W. You could do with a smaller
version (0.5W) there??

Mind you, I'm not trying to be negative about your design, but just curious
about some of your design decisions. The Luxeon's are really nice gadgets
8-)

Rob

Why not fuse the 12V line - that's what I wanted to do, but due to the
way I had done the board layout, it was simpler to fuse the ground
line. Besides, this is a fiberglass airplane, so it is unlikely to come
in contact with dangling ground wires. But your point is valid, and it
might be worth changing in the future.

I had not thought of the decoupling capacitor for the 7805. Again, a
good point.

I knew about the low power dissipation in the 0.69Ohm resistor. The
only reason I used a 3W resistor was because I wanted to use the same
board for both circuits. A smaller resistor in a big slot won't look as
pretty (I know, lame reason..)

Someone else brought up the point about switching regulators for
greater efficiency. Actually, the efficiency here is not all that bad.
The red-side transfers 50% power to the LED, and the green-side
transfers 80% power to the LED. Most switching regulators are around
80-90% efficient, so I concluded that switching regulators were not
worth the extra complexity and the possible RF interference to gain a
little bit of extra efficiency. In addition, most off-the-shelf
switching regulator chips put out constant voltages, so they would
still need a circuitry to convert to a constant current application (so
we are back to the same problem). Also, most off-the-shelf switching
regulators put out standard PC motherboard voltages (3.3V, 5.0V..), and
non-standard voltages would be costly components. I once tried to
design my own switching regulator, but I could not entirely isolate the
noise. I could hear a hiss on my FM radio.




Rob Turk wrote:
"Andrew Sarangan" wrote in message
oups.com...
Actually, those are current sensing resistors, not current limiting.
The voltage across the resistor is compared with a fixed reference
voltage, and it is the FET which limits the current. So, a higher
resistor does not necessarily mean lower current.


Ahh yes. I saw the current sensing resistors but I overlooked the resistor
values for the divider that creates the fixed reference. I'm still wondering
about a few things though, hope you can elaborate a bit.

- You have the fuse placed in the ground wire. However, the largest
'touchable' area on your PCB and heatsinks are all attached to the area
behind the fuse. A simple protruding screw or rivet would be enough to turn
the circuit into an unfused system. Why not fuse the 12V line?

- The LM7805 really likes having a small decoupling capacitor at it's output
to prevent oscillation (and even self-destrucion on cheap non-brand 7805's).
How about adding 100nF between the 5V output and ground?

- The current sense resistor in the 1400mA version will dissipate about (1.4
x 1.4 x 1.3) 2.6W, so a 3W resistor is OK. The 700mA version would only
dissipate (0.7 x 0.7 x 0.69) about 0.36 W. You could do with a smaller
version (0.5W) there??

Mind you, I'm not trying to be negative about your design, but just curious
about some of your design decisions. The Luxeon's are really nice gadgets
8-)

Rob

"Andrew Sarangan" wrote in message
oups.com...
Why not fuse the 12V line - that's what I wanted to do, but due to the
way I had done the board layout, it was simpler to fuse the ground
line. Besides, this is a fiberglass airplane, so it is unlikely to come
in contact with dangling ground wires. But your point is valid, and it
might be worth changing in the future.

I had not thought of the decoupling capacitor for the 7805. Again, a
good point.

I knew about the low power dissipation in the 0.69Ohm resistor. The
only reason I used a 3W resistor was because I wanted to use the same
board for both circuits. A smaller resistor in a big slot won't look as
pretty (I know, lame reason..)

Someone else brought up the point about switching regulators for
greater efficiency. Actually, the efficiency here is not all that bad.
The red-side transfers 50% power to the LED, and the green-side
transfers 80% power to the LED. Most switching regulators are around
80-90% efficient, so I concluded that switching regulators were not
worth the extra complexity and the possible RF interference to gain a
little bit of extra efficiency. In addition, most off-the-shelf
switching regulator chips put out constant voltages, so they would
still need a circuitry to convert to a constant current application (so
we are back to the same problem). Also, most off-the-shelf switching
regulators put out standard PC motherboard voltages (3.3V, 5.0V..), and
non-standard voltages would be costly components. I once tried to
design my own switching regulator, but I could not entirely isolate the
noise. I could hear a hiss on my FM radio.


The switching circuits I was referring to are not the 78xx equivalents of
standard voltage regulators. These Micropuck drivers are specifically
designed to drive Luxeon LED's, they are producing the correct drive current
for them and can be used with a wide input range (8-32V, making them
suitable for both 14V and 28V installations).

The RF interference is definitely something to worry about. With a metal
plane it should be easier to get things working OK but in a fibreglass plane
it may require extra decoupling attention.

For your own plane I can imagine you're not too worried about having
dangling ground wires, but note that because you published the design,
others may be encouraged to reproduce the design for their own plane.
Especially because you did such a great and professional looking job
documenting it, others may not think twice when applying it to their kit.
Safety first...

Rob

Andrew Sarangan wrote:
Recently I designed and built a nav light system for my Europa aircraft
using the Luxeon LEDs with great results.

I also measured the radiation pattern (after fitting the LEDs to the
aircraft) and compared it to the FAR specs. It exceeds the requirements
by 3-5 times, and draw only 2 Amps total. It is bright enough to almost
use as a landing light.

Actually, I am surprised that most manufacturers do not provide a
measured radiation pattern. They just say that it complies with the
FAR. Well, meeting the specs is not the same as exceeding it. Since
LEDs lose power with age, this could be an important consideration.

Just in case someone might find this useful, I wrote it up as an
article:
http://www.sarangan.org/aviation/eur...tip-Lights.pdf

Let me know what you think.


3 questions:

1) are the electronics going to survive vibration? I don't see any
isolation.

2) won't the reflector tend to oxidize fairly rapidly?

3) why use a fuse? Jim Weir did a rather nice article in Kitplanes®
awhile back discussing a solid state circuit breaker (I forget what it's
called) that might be a good idea.

I rather like the set up. Very good write up

Dan, U.S. Air Force, retired

Very good point about the reflector oxidation. I guess I should paint
it right away with reflective paint.

I looked at the solid state breakers you refer to. They are made of a
polymer, which opens the circuit when its temperature gets above a
preset limit. The reason I decided not to use those is because it is
strongly dependent on the ambient temperature. ie it will trip at
different currents when it is cold outside vs hot outside. This could
be a problem since the aircraft is likely to see large swings in
temperature from winter to summer, and at different altitudes. The
filament fuses are in a sealed glass tube, which is relatively
independent of temperature.

Mechanical vibration... The LEDs don't care about mechanical vibration
as much as regular lamps do. The electronics are all solid state, so
they won't care either. The solder joints might care, but if that were
the case, all other electronics in the cockpit will also be vulnerable.
I've built other electronics for the cockpit, and never had vibration
related problems. I could be wrong. I guess I will find out.

Thanks for your pointers. I will have to take them into
consideration...



Dan wrote:
Andrew Sarangan wrote:
Recently I designed and built a nav light system for my Europa aircraft
using the Luxeon LEDs with great results.

I also measured the radiation pattern (after fitting the LEDs to the
aircraft) and compared it to the FAR specs. It exceeds the requirements
by 3-5 times, and draw only 2 Amps total. It is bright enough to almost
use as a landing light.

Actually, I am surprised that most manufacturers do not provide a
measured radiation pattern. They just say that it complies with the
FAR. Well, meeting the specs is not the same as exceeding it. Since
LEDs lose power with age, this could be an important consideration.

Just in case someone might find this useful, I wrote it up as an
article:
http://www.sarangan.org/aviation/eur...tip-Lights.pdf

Let me know what you think.


3 questions:

1) are the electronics going to survive vibration? I don't see any
isolation.

2) won't the reflector tend to oxidize fairly rapidly?

3) why use a fuse? Jim Weir did a rather nice article in Kitplanes®
awhile back discussing a solid state circuit breaker (I forget what it's
called) that might be a good idea.

I rather like the set up. Very good write up

Dan, U.S. Air Force, retired

Impressive. Nice fab job. I'm also impressed that you measured
the radiation pattern and compared it to the FAR. Most people
wouldn't have done that.

Someone else mentioned about oxidation of the reflector, and that
is a potential problem, but easily solveable. I have seen metalized
plastic film that is stick on and highly reflective.

Someone else mentioned the possibility of changing your circuitry
to throttle back the LED current based on a temperature sensor.
Of course, if you do that you'll have to remeasure the radiation
patterns at the lowest current based on the highest ambient temp
that you expect to be operating at. The good thing is that your
nav lights are only required to be operating at night.

It seems to me that you could dispense with the cooling fan by
incorporating a large enough passive heat sink. My suggestion
would be to think along the lines of a big piece of really thin
aluminum. You could also use passive air cooling by ducting
some of the high pressure air from the lower side of the wing
over the heat sink, and out the back of the airfoil. Or, you
could just keep checking that the fan is working and replace it
when it craps out ;-)

Good work!

Don W.

Andrew Sarangan wrote:
Recently I designed and built a nav light system for my Europa aircraft
using the Luxeon LEDs with great results.

I also measured the radiation pattern (after fitting the LEDs to the
aircraft) and compared it to the FAR specs. It exceeds the requirements
by 3-5 times, and draw only 2 Amps total. It is bright enough to almost
use as a landing light.

Actually, I am surprised that most manufacturers do not provide a
measured radiation pattern. They just say that it complies with the
FAR. Well, meeting the specs is not the same as exceeding it. Since
LEDs lose power with age, this could be an important consideration.

Just in case someone might find this useful, I wrote it up as an
article:
http://www.sarangan.org/aviation/eur...tip-Lights.pdf

Let me know what you think.