1 watt and 5 watt LED for Nav lights?

[Bill]

To Jim Weir and Group

I am interested in using the new (to me) 1 watt and 5 watt LEDs for
nav lights.
Not having to worry about changing bulbs or the power requirements are
very attractive.

I have seen some posts about leds but would like to tie it all
together.
I know of two sites showing their versions and one is using 9 LEDs
while the other is using more.

What it boils down to is this: how many leds for the the right and
left wings, how many for the tail and can the leds be strobed or any
thing else I don't know?

Thanks
Bill

[Jim Weir]

I'm not sure anybody really "knows". We've seen some subjective comments like
"boy they are really bright" and "gee, they sure are green", but I do not
believe anybody has quantitative data as to whether the actual FAR optical
specification has been met.

OTOH, I've seen some comments in here about the FAR specification being so
loosey-goosey that two birthday candles inside a wine bottle strapped to the
wingtip would be OK.

As you say, I'd like to see some hard photometric data taken with calibrated
equipment and a checklist of HOW this particular installation meets the FAR.

Jim



(Bill)
shared these priceless pearls of wisdom:

->To Jim Weir and Group
->
->I am interested in using the new (to me) 1 watt and 5 watt LEDs for
->nav lights.



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Dean Head]

Just back from Sun-n-Fun and I saw Whelan has started to use LEDs. Picked up
there info but have not read it yet.

Dean
Cozy MK4
BKV FL

"Bill" > wrote in message
om...
> To Jim Weir and Group
>
> I am interested in using the new (to me) 1 watt and 5 watt LEDs for
> nav lights.
> Not having to worry about changing bulbs or the power requirements are
> very attractive.
>
> I have seen some posts about leds but would like to tie it all
> together.
> I know of two sites showing their versions and one is using 9 LEDs
> while the other is using more.
>
> What it boils down to is this: how many leds for the the right and
> left wings, how many for the tail and can the leds be strobed or any
> thing else I don't know?
>
> Thanks
> Bill

[anonymous coward]

Jim Weir wrote:

> I'm not sure anybody really "knows". We've seen some subjective comments
> like "boy they are really bright" and "gee, they sure are green", but I do
> not believe anybody has quantitative data as to whether the actual FAR
> optical specification has been met.
>
> OTOH, I've seen some comments in here about the FAR specification being so
> loosey-goosey that two birthday candles inside a wine bottle strapped to
> the wingtip would be OK.
>
> As you say, I'd like to see some hard photometric data taken with
> calibrated equipment and a checklist of HOW this particular installation
> meets the FAR.

I'm just browsing (i.e. not building a plane) so I haven't got the FAR
regulations to hand. But I've played with Luxeons quite a lot so this
piqued my interest. What exactly are the FAR requirements?

Luxeon provide some good photometric data on their LEDs on their website.
http://www.lumileds.com/products/documentation_index.html
They give peak wavelengths, CIE chromaticity co-ordinates,
spectrophotometric measurements, deviation with temperature, luminous
efficiency...

IIRC the red-orange 1w LED gives out 55 Lumens of light output - which is an
order of magnitude better than a filtered lightbulb. Other colours give out
considerably less light - but even the green LED will be more efficient
than a green-filtered xenon-flash tube, for example.

Then there's the matter of making sure the right amount of light goes in the
right directions.

AC
>
> Jim
>
>
>
> (Bill)
> shared these priceless pearls of wisdom:
>
> ->To Jim Weir and Group
> ->
> ->I am interested in using the new (to me) 1 watt and 5 watt LEDs for
> ->nav lights.
>
>
>
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com

[Ernest Christley]

anonymous coward wrote:
> Jim Weir wrote:
>
>
>>I'm not sure anybody really "knows". We've seen some subjective comments
>>like "boy they are really bright" and "gee, they sure are green", but I do
>>not believe anybody has quantitative data as to whether the actual FAR
>>optical specification has been met.
>>
>>OTOH, I've seen some comments in here about the FAR specification being so
>>loosey-goosey that two birthday candles inside a wine bottle strapped to
>>the wingtip would be OK.
>>
>>As you say, I'd like to see some hard photometric data taken with
>>calibrated equipment and a checklist of HOW this particular installation
>>meets the FAR.
>
>
> I'm just browsing (i.e. not building a plane) so I haven't got the FAR
> regulations to hand. But I've played with Luxeons quite a lot so this
> piqued my interest. What exactly are the FAR requirements?
>
> Luxeon provide some good photometric data on their LEDs on their website.
> http://www.lumileds.com/products/documentation_index.html
> They give peak wavelengths, CIE chromaticity co-ordinates,
> spectrophotometric measurements, deviation with temperature, luminous
> efficiency...
>
> IIRC the red-orange 1w LED gives out 55 Lumens of light output - which is an
> order of magnitude better than a filtered lightbulb. Other colours give out
> considerably less light - but even the green LED will be more efficient
> than a green-filtered xenon-flash tube, for example.
>
> Then there's the matter of making sure the right amount of light goes in the
> right directions.
>
> AC
>
>>Jim
>>
>>
>>
(Bill)
>>shared these priceless pearls of wisdom:
>>
>>->To Jim Weir and Group
>>->
>>->I am interested in using the new (to me) 1 watt and 5 watt LEDs for
>>->nav lights.
>>
>>
>>
>>Jim Weir (A&P/IA, CFI, & other good alphabet soup)
>>VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
>>http://www.rst-engr.com
>
>

The problem is that everyone uses a different yardstick to measure the
light output, and not all the yardsticks measure length.

Which would you rather have over your shop bench, one of those tiny LED
that are so bright you have to blink, or an 8ft flourescent that you can
stare at all day? Candles, watts, candella, lux, lumens...the terms go
on and on and what the FAA specifies may have more to do with
measurement convenience than they do safety. It's been a while, but the
FAA chose measurements that emphasize total light output, while all the
LED manufacturers use metrics that emphasize intensity.

Your tail light will cover the rear out to a 70* angle on each side, for
a 140* sweep. The marker light cover from directly ahead, back to the
70* mark.(Draw a circle and mark it off in 3 quadrants and you'll see
hwo this makes sense). Allmost all the ouput intensity is concentrated
on the level with it tapering to about 5% of the max at 85* up and down.
Note these are minimum values. More intensity is always a good thing.

I'm at work, but I'm thinking that it is all in FAR23-1490 (or within a
few paragraphs thereof).


--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

[Dave S]

Whelen is now selling LED nav lights.. green and red. I wonder if their
data (intensity, wavelenth) is readily available.. so they can show
proof of their compliance.

Dave

Ernest Christley wrote:
> anonymous coward wrote:
>
>> Jim Weir wrote:
>>
>>
>>> I'm not sure anybody really "knows". We've seen some subjective
>>> comments
>>> like "boy they are really bright" and "gee, they sure are green", but
>>> I do
>>> not believe anybody has quantitative data as to whether the actual FAR
>>> optical specification has been met.
>>>
>>> OTOH, I've seen some comments in here about the FAR specification
>>> being so
>>> loosey-goosey that two birthday candles inside a wine bottle strapped to
>>> the wingtip would be OK.
>>>
>>> As you say, I'd like to see some hard photometric data taken with
>>> calibrated equipment and a checklist of HOW this particular installation
>>> meets the FAR.
>>
>>
>>
>> I'm just browsing (i.e. not building a plane) so I haven't got the FAR
>> regulations to hand. But I've played with Luxeons quite a lot so this
>> piqued my interest. What exactly are the FAR requirements?
>>
>> Luxeon provide some good photometric data on their LEDs on their website.
>> http://www.lumileds.com/products/documentation_index.html
>> They give peak wavelengths, CIE chromaticity co-ordinates,
>> spectrophotometric measurements, deviation with temperature, luminous
>> efficiency...
>>
>> IIRC the red-orange 1w LED gives out 55 Lumens of light output - which
>> is an
>> order of magnitude better than a filtered lightbulb. Other colours
>> give out
>> considerably less light - but even the green LED will be more efficient
>> than a green-filtered xenon-flash tube, for example.
>>
>> Then there's the matter of making sure the right amount of light goes
>> in the
>> right directions.
>>
>> AC
>>
>>> Jim
>>>
>>>
>>>
>>> (Bill)
>>> shared these priceless pearls of wisdom:
>>>
>>> ->To Jim Weir and Group
>>> ->
>>> ->I am interested in using the new (to me) 1 watt and 5 watt LEDs for
>>> ->nav lights.
>>>
>>>
>>>
>>> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
>>> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
>>> http://www.rst-engr.com
>>
>>
>>
>
> The problem is that everyone uses a different yardstick to measure the
> light output, and not all the yardsticks measure length.
>
> Which would you rather have over your shop bench, one of those tiny LED
> that are so bright you have to blink, or an 8ft flourescent that you can
> stare at all day? Candles, watts, candella, lux, lumens...the terms go
> on and on and what the FAA specifies may have more to do with
> measurement convenience than they do safety. It's been a while, but the
> FAA chose measurements that emphasize total light output, while all the
> LED manufacturers use metrics that emphasize intensity.
>
> Your tail light will cover the rear out to a 70* angle on each side, for
> a 140* sweep. The marker light cover from directly ahead, back to the
> 70* mark.(Draw a circle and mark it off in 3 quadrants and you'll see
> hwo this makes sense). Allmost all the ouput intensity is concentrated
> on the level with it tapering to about 5% of the max at 85* up and down.
> Note these are minimum values. More intensity is always a good thing.
>
> I'm at work, but I'm thinking that it is all in FAR23-1490 (or within a
> few paragraphs thereof).
>
>

[Jay]

Using the web, I found in part 23 section 23.1391 a list of the
intensity (candels) by angle required. From what it looks like,
someone measured the system that was already being made (a bulb and
filter) and put in in the book. So what this means is that you're
stuck emulating a technology inferior in almost every way using a new
technology. The spec emphasizes what light bulbs do well (high flux,
even illumination) and de-emphasizes what it doesn't (spectral purity,
reliability).

You could probably do the math from the minimum guaranteed intensity
and the beam shapes and meet the spec on paper, but it would be nice
to actually measure it. You can buy equipment to do this if you want
to add to your tool box yet another single purpose tool.

The other issue is that the manufacturer beam shapes are really a
little bogus because the high intensity LEDs use clear lenses and
actually project an image of the semiconductor chip inside. So
instead of a nice round shape, you get a picture of a little bright
chicklet and reflector cup.

So how many LEDs? Depends on if your using "typical" or minumum
guaranteed intensity. Depends on what direction you array them,
depends on what bin they came from, depends on a lot of things.




(Bill) wrote in message >...
> To Jim Weir and Group
>
> I am interested in using the new (to me) 1 watt and 5 watt LEDs for
> nav lights.
> Not having to worry about changing bulbs or the power requirements are
> very attractive.
>
> I have seen some posts about leds but would like to tie it all
> together.
> I know of two sites showing their versions and one is using 9 LEDs
> while the other is using more.
>
> What it boils down to is this: how many leds for the the right and
> left wings, how many for the tail and can the leds be strobed or any
> thing else I don't know?
>
> Thanks
> Bill

[Dean Head]

Ok, Looked at the retro units at SNF and the associated specs. Red/green/
TSO'ed position lights. Contains 7 elements (appeared to be the Luxeon
style. 28 v @ .35 A for the total draw....looks like they are using the 1
watt style. Arrayed 2 rows 3 and 4 to a row. Don't see why we could not
build something similar from materials now available.

BTW, the list price is $460 each (WOW)

Dean
Cozy MK4
Bkv FL

"Bill" > wrote in message
om...
> To Jim Weir and Group
>
> I am interested in using the new (to me) 1 watt and 5 watt LEDs for
> nav lights.
> Not having to worry about changing bulbs or the power requirements are
> very attractive.
>
> I have seen some posts about leds but would like to tie it all
> together.
> I know of two sites showing their versions and one is using 9 LEDs
> while the other is using more.
>
> What it boils down to is this: how many leds for the the right and
> left wings, how many for the tail and can the leds be strobed or any
> thing else I don't know?
>
> Thanks
> Bill

[jerry Wass]

BTW--Does anyone have the conversion factor to change yard lard-lamps to
foot candles ??

Bill wrote:

> To Jim Weir and Group
>
> I am interested in using the new (to me) 1 watt and 5 watt LEDs for
> nav lights.
> Not having to worry about changing bulbs or the power requirements are
> very attractive.
>
> I have seen some posts about leds but would like to tie it all
> together.
> I know of two sites showing their versions and one is using 9 LEDs
> while the other is using more.
>
> What it boils down to is this: how many leds for the the right and
> left wings, how many for the tail and can the leds be strobed or any
> thing else I don't know?
>
> Thanks
> Bill

[Ernest Christley]

Dean Head wrote:
> Ok, Looked at the retro units at SNF and the associated specs. Red/green/
> TSO'ed position lights. Contains 7 elements (appeared to be the Luxeon
> style. 28 v @ .35 A for the total draw....looks like they are using the 1
> watt style. Arrayed 2 rows 3 and 4 to a row. Don't see why we could not
> build something similar from materials now available.
>
> BTW, the list price is $460 each (WOW)
>
> Dean
> Cozy MK4
> Bkv FL
>

But you gotta remember, Dean, these are aircraft quality LEDs they're a
usin'. You can't get these LEDs from just any SuperBright LED supplier,
and you definitely won't get a paper trail that says they are in fact
"SuperBright LEDs". You get what you pay for.

(Now removing tongue from cheek)

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

[Jeff Peterson]

Eric Jones wrote an nice description of leds as nav and strobe lights here:

http://www.periheliondesign.com/downloads/Aircraft%20Beacons%20Using%20LEDs.pdf

the rear and side strobes are fairly easy do with about 5 ea 5 watt luxeons

i used 6 in my tail strobe.

the required strobe intensity in the forward direction is a bit
tougher to accomplish with LEDs. still possible.

i think for my tail strobe i will uses 50% duty cycle.
not as "flashy" as a quick pulse, but actually easier see at a distance.

the human eye averages for 200 ms so for quick pulses its the
total light energy in the pulse that matters. stobes cant make long pulses
but LEDs can, so long pulses are the right choice with leds.


circuit will be like this

IRF2804
---------
| | |----parallel LEDs----Resistor----+12V
| LM555 |--------|
| | |-----gnd
---------

the 2804 is WAY overkill. it can switch 100s of amps. but its only 3 bucks,
so why not use the best.

i ordered a handful and when i get back form snf i will give the circuit a try.

-Jeff

[Jay]

I'd modify the circuit like this...
>
>
>
> |----serial LEDs(3?)----Resistor----+12V
> |----serial LEDs(3?)----Resistor----+12V
> |
> | repeat as necessary...
> |
> |----serial LEDs(3?)----Resistor----+12V
> --------- |----serial LEDs(3?)----Resistor----+12V
> | | |
> | LM555 |------|
> | | |-----gnd
> --------- IRF2804

By putting the LEDs in series instead of parallel you'll cut the
current drain by 2/3 (in the case of 3 leds series). Also with each
leg having its own resistor the LEDs don't have to be matched by
forward voltage.

Regards

(Jeff Peterson) wrote in message >...
> Eric Jones wrote an nice description of leds as nav and strobe lights here:
>
> http://www.periheliondesign.com/downloads/Aircraft%20Beacons%20Using%20LEDs.pdf
>
> the rear and side strobes are fairly easy do with about 5 ea 5 watt luxeons
>
> i used 6 in my tail strobe.
>
> the required strobe intensity in the forward direction is a bit
> tougher to accomplish with LEDs. still possible.
>
> i think for my tail strobe i will uses 50% duty cycle.
> not as "flashy" as a quick pulse, but actually easier see at a distance.
>
> the human eye averages for 200 ms so for quick pulses its the
> total light energy in the pulse that matters. stobes cant make long pulses
> but LEDs can, so long pulses are the right choice with leds.
>
>
> circuit will be like this
>
> IRF2804
> ---------
> | | |----parallel LEDs----Resistor----+12V
> | LM555 |--------|
> | | |-----gnd
> ---------
>
> the 2804 is WAY overkill. it can switch 100s of amps. but its only 3 bucks,
> so why not use the best.
>
> i ordered a handful and when i get back form snf i will give the circuit a try.
>
> -Jeff

[anonymous coward]

Jay wrote:

> Using the web, I found in part 23 section 23.1391 a list of the
> intensity (candels) by angle required. From what it looks like,
> someone measured the system that was already being made (a bulb and
> filter) and put in in the book. So what this means is that you're
> stuck emulating a technology inferior in almost every way using a new
> technology. The spec emphasizes what light bulbs do well (high flux,
> even illumination) and de-emphasizes what it doesn't (spectral purity,
> reliability).
>
> You could probably do the math from the minimum guaranteed intensity
> and the beam shapes and meet the spec on paper, but it would be nice
> to actually measure it. You can buy equipment to do this if you want
> to add to your tool box yet another single purpose tool.
>
> The other issue is that the manufacturer beam shapes are really a
> little bogus because the high intensity LEDs use clear lenses and
> actually project an image of the semiconductor chip inside. So
> instead of a nice round shape, you get a picture of a little bright
> chicklet and reflector cup.

This is very true for the LEDs with a very narrow beam (half angles down to
8-degrees or so) - but luxeons give a much broader beam and for whatever
reason this isn't the case in my experience (lambertian beam pattern only).
You can buy an optical widget that fits over the LED to make a narrower
beam again, and IMO your criticism is very valid for this case.

A solution is to shine the LEDs through some five or ten-degree holographic
diffusing filter from the POC (Physical Optics Corporation - if memory
serves). They're nice people to deal with, and were giving out free 1"
samples last time I asked.

AC
>
> So how many LEDs? Depends on if your using "typical" or minumum
> guaranteed intensity. Depends on what direction you array them,
> depends on what bin they came from, depends on a lot of things.
>
>
>
>
> (Bill) wrote in message
> >...
>> To Jim Weir and Group
>>
>> I am interested in using the new (to me) 1 watt and 5 watt LEDs for
>> nav lights.
>> Not having to worry about changing bulbs or the power requirements are
>> very attractive.
>>
>> I have seen some posts about leds but would like to tie it all
>> together.
>> I know of two sites showing their versions and one is using 9 LEDs
>> while the other is using more.
>>
>> What it boils down to is this: how many leds for the the right and
>> left wings, how many for the tail and can the leds be strobed or any
>> thing else I don't know?
>>
>> Thanks
>> Bill

[Dean Head]

Jeff,
Who did you order the 2804's from?
Thanks
Dean

"Jeff Peterson" > wrote in message
om...
> Eric Jones wrote an nice description of leds as nav and strobe lights
here:
>
>
http://www.periheliondesign.com/downloads/Aircraft%20Beacons%20Using%20LEDs.pdf
>
> the rear and side strobes are fairly easy do with about 5 ea 5 watt
luxeons
>
> i used 6 in my tail strobe.
>
> the required strobe intensity in the forward direction is a bit
> tougher to accomplish with LEDs. still possible.
>
> i think for my tail strobe i will uses 50% duty cycle.
> not as "flashy" as a quick pulse, but actually easier see at a distance.
>
> the human eye averages for 200 ms so for quick pulses its the
> total light energy in the pulse that matters. stobes cant make long pulses
> but LEDs can, so long pulses are the right choice with leds.
>
>
> circuit will be like this
>
> IRF2804
> ---------
> | | |----parallel LEDs----Resistor----+12V
> | LM555 |--------|
> | | |-----gnd
> ---------
>
> the 2804 is WAY overkill. it can switch 100s of amps. but its only 3
bucks,
> so why not use the best.
>
> i ordered a handful and when i get back form snf i will give the circuit a
try.
>
> -Jeff

[Jay]

You can get all the parts from Digi-key for less than $10 +S/H except
those fancy LEDs.

Regards


"Dean Head" > wrote in message >...
> Jeff,
> Who did you order the 2804's from?
> Thanks
> Dean

[Jeff Peterson]

"Dean Head" > wrote in message >...
> Jeff,
> Who did you order the 2804's from?
> Thanks
> Dean
digikey.

built the circuit today and will post photos and schematic soon

-Jeff

[Dean Head]

Jeff,

Anxious to see the results. I am thinking of some pretty slick ways to embed
these into my Cozy winglets. I hope to find a way to replace the Xenon
strobes completely.

Dean

"Jeff Peterson" > wrote in message
om...
> "Dean Head" > wrote in message
>...
> > Jeff,
> > Who did you order the 2804's from?
> > Thanks
> > Dean
> digikey.
>
> built the circuit today and will post photos and schematic soon
>
> -Jeff

[Jeff Peterson]

(Jay) wrote in message >...
> I'd modify the circuit like this...
> >
> >
> >
> > |----serial LEDs(3?)----Resistor----+12V
> > |----serial LEDs(3?)----Resistor----+12V
> > |
> > | repeat as necessary...
> > |
> > |----serial LEDs(3?)----Resistor----+12V
> > --------- |----serial LEDs(3?)----Resistor----+12V
> > | | |
> > | LM555 |------|
> > | | |-----gnd
> > --------- IRF2804
>
> By putting the LEDs in series instead of parallel you'll cut the
> current drain by 2/3 (in the case of 3 leds series). Also with each
> leg having its own resistor the LEDs don't have to be matched by
> forward voltage.
>
> Regards
>
yes, individual resistors make sense. i did switch to this scheme.

turns out, for the six leds that i used in the tail strobe, the
forward voltages match well enough to allow parallel connection. but
i still used individual resitors.

the white luxeons have a forward voltage too high to allow series
conncetion of the leds (with a 12 v system).

-Jeff

[Jay]

(Jeff Peterson) wrote in message > yes, individual resistors make sense. i did switch to this scheme.
>
> turns out, for the six leds that i used in the tail strobe, the
> forward voltages match well enough to allow parallel connection. but
> i still used individual resitors.
>
> the white luxeons have a forward voltage too high to allow series
> conncetion of the leds (with a 12 v system).
>
> -Jeff

What is the forward voltage on those parts? You should put as many in
series as you can get away with. So if the forward voltage is really
high, maybe you go with parllel strings of series 2 or whatever. The
degree to which you can string them in series effects the efficiency
of the lighting system (luminous flux/power consumed).

[BllFs6]

Hi Guys...

Havent followed this thread carefully...been away for awhile...so forgive me if
this has been covered already...

There is one disadvantage to using mostly the forward voltage drop of a LED to
"span" the battery voltage ...as opposed to say a big resistor taking a good
fraction of the voltage drop...

An LED's voltage drop/resistance is pretty temp dependent....

And here is what can happen....the LED gets warm.....resistance drops....more
power flows through....LED gets warmer still...still more power
flows....warmer,more power....can easily become a runaway situation...leading
to burnout or even worse a fire somewhere in the electrical cicuit..

Now, this isnt much of a problem in very low powered LEDS, but in high powered
ones that get warm to touch just sitting on the bench, its something you need
to worry about....

If you have a circuit in mind...you need to make it and THEN run it in absolute
hottest environment at the absolute highest voltage it will ever see (ie the 14
or whatever volts is MAX from the alternator rather than the nominal 12 from
the battery)....then if that works and current limits werent exceeded back the
power flow down say 10 to 20 percent just to be safe....

What the max temp of a "lexan lighting housing" at the tip of a wing in August
on a no wind day sitting on a black asphalt runway at high noon in Texas?

I can easily imagine it being 60 degrees or more than the temp you tested it in
on the bench.....so just because it didnt suffer thermal runaway on the bench
doesnt tell you much about how it"ll behave in the plane....

Another related problem is if you have multiple parallel LED/resistor paths
running from the same voltage source....at room temp you may test the setup and
each path is taking the same power....but then there is that pesky
temp/resistance property of the LEDs...if they are different enough, when your
setup is run in a higher temp or poor cooling conditions....one path may become
a significantly lower resistance path than the other (the resistors can cause
it as well)...and all of a sudden you have way more power flowing through one
path than was intended to....and you have another thermal runaway situation...

Which brings up fuses....lets say you 3 parallel LED resistor paths, running
off of one wire pair that runs out the wing tips....

You design it so each branch takes a bit under 5 amps, so you have that wire
pair fused at 15 amps....

If you suffer something like one dead branch in combo with a thermal runaway of
another branch (or even perhaps just a thermal runaway of one branch)....you
can have a situation where one branch is WAY exceeding its design limits...yet
the total power isnt enough to trip the fuse back in the cockpit...

So, EACH branch should be fused seperately in addition to the main overall wire
fuse...

Now, if youve designed and tested your circuit worth a hoot the chances of one
branch going amook are pretty low, so something like "semi permanent" circuit
board fuses soldered into each branch probably make more sense and would
provide better reliability than removeable fuses...

Another thing....precision resistors, temp stable resistors, and even resistors
with a significant negative temp coefficient ARENT that expensive compared to
other expensense for an airplane/high powered LED project....so the might be
worth investigating, especially since your only talking a handful of them and
they could significantly ease your engineering problems as well as improve the
reliability of the setup...

Just my 10 cents....

take care

Blll

[Jay]

With a properly biased LED stack and resistor there is no thermal
runaway problem. I've never seen or heard of this happening to
anyone. The slope of the diodes once they go past the knee in
combination with the series resistor more than makes up for a small
negative temp coefficient of the diodes. Maybe what you're saying is
that you need some minimum resistance as a percentage of the total
drop to guarantee stability, and this I would agree with.

And I totally agree, prototype one leg of the circuit, and run it over
voltage and temp (hit your corners) before you build it into your
wing.

Fuses- I'd still go with the standard central fuse/breaker panel.
Since its a non-inductive load, you should be able to use a
fuse/breaker without much over rating.

I'm a big believer in keeping things simple. But often times a simple
final product requires complex analysis and testing. The most complex
implementations often reflect design with less than well understood
inputs.



(BllFs6) wrote in message >...
> Hi Guys...
>
> Havent followed this thread carefully...been away for awhile...so forgive me if
> this has been covered already...
>
> There is one disadvantage to using mostly the forward voltage drop of a LED to
> "span" the battery voltage ...as opposed to say a big resistor taking a good
> fraction of the voltage drop...
>
> An LED's voltage drop/resistance is pretty temp dependent....
>
> And here is what can happen....the LED gets warm.....resistance drops....more
> power flows through....LED gets warmer still...still more power
> flows....warmer,more power....can easily become a runaway situation...leading
> to burnout or even worse a fire somewhere in the electrical cicuit..
>
> Now, this isnt much of a problem in very low powered LEDS, but in high powered
> ones that get warm to touch just sitting on the bench, its something you need
> to worry about....
>
> If you have a circuit in mind...you need to make it and THEN run it in absolute
> hottest environment at the absolute highest voltage it will ever see (ie the 14
> or whatever volts is MAX from the alternator rather than the nominal 12 from
> the battery)....then if that works and current limits werent exceeded back the
> power flow down say 10 to 20 percent just to be safe....
>
> What the max temp of a "lexan lighting housing" at the tip of a wing in August
> on a no wind day sitting on a black asphalt runway at high noon in Texas?
>
> I can easily imagine it being 60 degrees or more than the temp you tested it in
> on the bench.....so just because it didnt suffer thermal runaway on the bench
> doesnt tell you much about how it"ll behave in the plane....
>
> Another related problem is if you have multiple parallel LED/resistor paths
> running from the same voltage source....at room temp you may test the setup and
> each path is taking the same power....but then there is that pesky
> temp/resistance property of the LEDs...if they are different enough, when your
> setup is run in a higher temp or poor cooling conditions....one path may become
> a significantly lower resistance path than the other (the resistors can cause
> it as well)...and all of a sudden you have way more power flowing through one
> path than was intended to....and you have another thermal runaway situation...
>
> Which brings up fuses....lets say you 3 parallel LED resistor paths, running
> off of one wire pair that runs out the wing tips....
>
> You design it so each branch takes a bit under 5 amps, so you have that wire
> pair fused at 15 amps....
>
> If you suffer something like one dead branch in combo with a thermal runaway of
> another branch (or even perhaps just a thermal runaway of one branch)....you
> can have a situation where one branch is WAY exceeding its design limits...yet
> the total power isnt enough to trip the fuse back in the cockpit...
>
> So, EACH branch should be fused seperately in addition to the main overall wire
> fuse...
>
> Now, if youve designed and tested your circuit worth a hoot the chances of one
> branch going amook are pretty low, so something like "semi permanent" circuit
> board fuses soldered into each branch probably make more sense and would
> provide better reliability than removeable fuses...
>
> Another thing....precision resistors, temp stable resistors, and even resistors
> with a significant negative temp coefficient ARENT that expensive compared to
> other expensense for an airplane/high powered LED project....so the might be
> worth investigating, especially since your only talking a handful of them and
> they could significantly ease your engineering problems as well as improve the
> reliability of the setup...
>
> Just my 10 cents....
>
> take care
>
> Blll

[Bill]

(Bill) wrote in message >...
> To Jim Weir and Group
>
> I am interested in using the new (to me) 1 watt and 5 watt LEDs for
> nav lights.
> Not having to worry about changing bulbs or the power requirements are
> very attractive.
>
> I have seen some posts about leds but would like to tie it all
> together.
> I know of two sites showing their versions and one is using 9 LEDs
> while the other is using more.
>
> What it boils down to is this: how many leds for the the right and
> left wings, how many for the tail and can the leds be strobed or any
> thing else I don't know?
>
> Thanks
> Bill


Lots of good stuff here. Now if I just knew what it all meant?

Can someone sum it all up and tell a "I can solder a wire" person what
they can do to build these?

Thanks
Bill