Today's Message Index:
----------------------
1. 06:29 AM - Re: Re: Re: Re: Re: LED experiment (Eric M. Jones)
2. 11:17 AM - Fw: Preflight Check List Item - 0.8V (Rick Fogerson)
3. 12:19 PM - Help with Visio 2000 (James Foerster)
4. 05:07 PM - Re: LED Tail Lights (Eric M. Jones)
5. 05:38 PM - Re: Help with Visio 2000 (Chad Robinson)
6. 09:40 PM - Re: Re: LED Tail Lights (Ernest Christley)
Message 1
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| Subject: | Re: Re: RE: Re: Re: LED experiment |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
--> AeroElectric-List message posted by: mprather <mprather@spro.net>
>For this thought model to be representative of reality, the distance from
each LED
>to the surface of the dome must be "large" compared to the distance between
each
>LED. Consider this: If the radius of the dome was 1meter (3feet), and
>each LED was mounted 0.01meters (1/4inch) from it's surface (evenly
distributed),
>the dome would have 67 discreet spots on it, which wouldn't look very
uniform.
>Eric, please correct me if I am wrong.
>Regards, Matt-
Matt---you are exactly right as always. Employing a bunch of conical
emitters to make a hemispherically smooth emitting light source is what I
was aiming at.
Thanks,
Eric
Message 2
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| Subject: | Fw: Preflight Check List Item - 0.8V |
--> AeroElectric-List message posted by: "Rick Fogerson" <rickf@cableone.net>
Do not archive ----- Original Message -----
From: Rick Fogerson
Subject: Preflight Check List Item - 0.8V
Hi Bob,
There was a preflight item you recommended I check on my RV 6A that had to do with
0.8 Volts and the essential bus. It's been 5 years since I've owned the airplane.
Is the test still recommended and if it is could you refresh my memory
on how the test was done and what it accomplished.
Thanks, Rick Fogerson
Message 3
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| Subject: | Help with Visio 2000 |
--> AeroElectric-List message posted by: "James Foerster" <jmfpublic@comcast.net>
All,
I have Visio 2000, professional edition. There is also a technical edition, and
I suspect the difference is the library of "solutions", or example templates.
Does anyone have a file of these for electrical schematics? I did download
the library of symbols kindly created by Chad Robinson.
I did sucessfully download fig.14 in .dwg format into the program, but I'm not
sure how to proceed, as I'm just learning Visio. I think I need an electric schematic
template, but I'm not sure.
Jim Foerster
Message 4
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| Subject: | Re: LED Tail Lights |
--> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
LED Tail Lights----
Dig out your books on solid geometry and photometry.
Okay, the FAA wants 20 cd in spherical wedge 70 degrees on each side of the
airplanes tail.
The area of the curved surface of this wedge at 1 meter radius is 4.9 m sq.
(The exercise is left to the student).
If the light source is 20 cd, then we expect 20 lux on this surface (you can
measure it with an incidence [lux] photometer).
So we need "X Lumens"/4.9 meters=20 cd. Solve for "X Lumens" and we get
about 100 lumens.
Now lumens (lm) are the standard unit of photometric Stuff---think of
lumens as real matter like oatmeal. Furthermore, Lumens/Watt is the
fundamental way of describing the efficiency of light sources; how much
light gets made from how much electricityand presently both high-efficiency
leds and tungsten-halogen lamps are in the 25 lumens/watt range.
This 100 lumens is easy to get in an LED like the Luxeon V Portable. This
LED is 5 Watts 88-120 lumens of white light and is the LED in my white LED
tail light. I have measure this and it satisfies the FAA requirements--but
without a huge margin. And this $45 LED dissipates 5 watts of heat. Keeping
the temperature down is critical to enjoying the LEDs long life.
So if one were to build a tail light out of SuperBright LEDs like RL5-W2545
(3750 mcd at 30mA , 45 degrees coverage), you would expect the same
dissipation per lumen--that is you would expect 5 watts of heat. Since the
package dissipates only 80 mW (and physically cannot be made to dissipate
more), you would expect 63 LEDs would be necessary. This is not in close
agreement particularly, with my earlier estimates, but we are only
estimating here from the heat loss given that both LEDs are about the same
efficiency, not the actual photometry. The Luxeon is spectacularly good
optically, while the 5 mm package of the RL5 is not so good and gets much
worse with adhesives and solventsso you would need a lot more LEDs.
I have shown this calculation elsewhere, so I won't whip that horse again
here.
My white LED tail light is designed to be used with the supplied current
regulator since there is a temperature coefficient involved in the LED and
any ballast resistor employed. Likewise the ageing characteristics might
change the current in way I could not entirely predictand aircraft
electrical systems can be a range of voltages. The current regulator is 700
mA +/- 1 mA over its temperature and voltage range.
Be aware that I would be the last person to pooh-pooh LED tail lights or any
other lights. I love them. But do the engineering involved before believing
that the job is done. Mythose shining lights do look convincing----but are
they right?
Regards,
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge MA 01550-2705
Phone (508) 764-2072
Email: emjones@charter.net
"Nothing is too wonderful to be true."
James Clerk Maxwell, discoverer of electromagnetism
"Too much of a good thing can be wonderful."
Mae West, discoverer of personal magnetism
Message 5
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| Subject: | Re: Help with Visio 2000 |
--> AeroElectric-List message posted by: Chad Robinson <crj@lucubration.com>
James Foerster wrote:
> --> AeroElectric-List message posted by: "James Foerster"
> <jmfpublic@comcast.net>
>
> All,
>
> I have Visio 2000, professional edition. There is also a technical
> edition, and I suspect the difference is the library of "solutions", or
> example templates. Does anyone have a file of these for electrical
> schematics? I did download the library of symbols kindly created by Chad
> Robinson.
>
> I did sucessfully download fig.14 in .dwg format into the program, but I'm
> not sure how to proceed, as I'm just learning Visio. I think I need an
> electric schematic template, but I'm not sure.
James, you don't need Technical Edition unless you want to import AutoCAD
files into Visio. In your case there should be no need, that was the purpose
of my work creating the stencil.
Open Visio and start a new drawing. Download the stencil file if you haven't
already, and use File->Open Stencil to open it. Then drag symbols from the
stencil into your drawing. Visio has a tool you can use to draw wires
connecting components, and there are tiny blue 'X' marks on each component
that act as endpoints for the wires. One nice feature of Visio is that if you
drag an object, connected wires follow it. Play around, you'll quickly get the
hang of the basics.
I have an example of my own planned system in the Orion->Chapter 22 portion of
my site. If it would help I can upload the Visio file for this, but since it's
based on a manual battery switch it's probably not too similar to what
everybody else is planning.
Regards,
Chad
Message 6
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| Subject: | Re: LED Tail Lights |
--> AeroElectric-List message posted by: Ernest Christley <echristley@nc.rr.com>
Eric M. Jones wrote:
> --> AeroElectric-List message posted by: "Eric M. Jones" <emjones@charter.net>
>
> LED Tail Lights----
>
> Dig out your books on solid geometry and photometry.
>
> Okay, the FAA wants 20 cd in spherical wedge 70 degrees on each side of the
> airplanes tail.
>
> The area of the curved surface of this wedge at 1 meter radius is 4.9 m sq.
> (The exercise is left to the student).
>
The surface area of a sphere is 4*pi*r
2, or 12.56 in this case. We
only cover 140 degrees with the tail light, so (140/360)*12.56 is 4.88.
That's the easy part. Now consider that 20 degrees from the
horizontal, the light should only be at only half power, and drops of to
nearly nothing quickly thereafter. Full power should be confined to a
20x140 degree box on the sphere surface. An exact computation requires
a double integral, but 1/3rd of the area is close enough. Now we're
down to 1.6 or so.
> If the light source is 20 cd, then we expect 20 lux on this surface (you can
> measure it with an incidence [lux] photometer).
>
No, we don't expect that. You might, but I certainly wouldn't. One lux
is equal to 0.0929 footcandles. 20 footcandles would be only 1.9 lux.
> So we need "X Lumens"/4.9 meters=20 cd. Solve for "X Lumens" and we get
> about 100 lumens.
x = 1.6 / 1.858 = .86 lumen
>
> Now lumens (lm) are the standard unit of photometric Stuff---think of
> lumens as real matter like oatmeal. Furthermore, Lumens/Watt is the
> fundamental way of describing the efficiency of light sources; how much
> light gets made from how much electricityand presently both high-efficiency
> leds and tungsten-halogen lamps are in the 25 lumens/watt range.
>
> This 100 lumens is easy to get in an LED like the Luxeon V Portable. This
> LED is 5 Watts 88-120 lumens of white light and is the LED in my white LED
> tail light. I have measure this and it satisfies the FAA requirements--but
> without a huge margin. And this $45 LED dissipates 5 watts of heat. Keeping
> the temperature down is critical to enjoying the LEDs long life.
>
> So if one were to build a tail light out of SuperBright LEDs like RL5-W2545
> (3750 mcd at 30mA , 45 degrees coverage), you would expect the same
> dissipation per lumen--that is you would expect 5 watts of heat. Since the
> package dissipates only 80 mW (and physically cannot be made to dissipate
> more), you would expect 63 LEDs would be necessary. This is not in close
> agreement particularly, with my earlier estimates, but we are only
> estimating here from the heat loss given that both LEDs are about the same
> efficiency, not the actual photometry. The Luxeon is spectacularly good
> optically, while the 5 mm package of the RL5 is not so good and gets much
> worse with adhesives and solventsso you would need a lot more LEDs.
>
It's called efficacy and is just a measurement of the efficiency of a
light source. All modern clear LEDs going to be nearly identical. All
the Luxeon is a clever package that get more diodes into a confined
space. That is neither necessary or possibly even desirable in this
case. Consider putting a 3/8" radius on a piece of plexiglass and using
it on a trailing edge. Embed the LEDs and eliminate a couple bulges.
> I have shown this calculation elsewhere, so I won't whip that horse again
> here.
>
This returns us to the original need. Replacing a expensive light
(cost, maintanence and headache), that uses excess power to produce
> My white LED tail light is designed to be used with the supplied current
> regulator since there is a temperature coefficient involved in the LED and
> any ballast resistor employed. Likewise the ageing characteristics might
> change the current in way I could not entirely predictand aircraft
> electrical systems can be a range of voltages. The current regulator is 700
> mA +/- 1 mA over its temperature and voltage range.
>
I discussed how to allow for reasonable voltage variances, and the
operating temperature varies from -30 to +70 degrees Celcius. I'd bet
money that the components in your regulator aren't rated to operate very
far out of that range (and who want's to fly when the temps are over
140). The simple diode's characteristics will vary no more over it's
useful life than a regulator (the useful life hereby defined as the life
of the airframe). In this situation, the regulator is just a heating
element that provides you with nothing but additional failure modes.
> Be aware that I would be the last person to pooh-pooh LED tail lights or any
> other lights. I love them. But do the engineering involved before believing
> that the job is done. Mythose shining lights do look convincing----but are
> they right?
And when you do the engineering, either use metric or british
measurements throughout. It's unseemly to switch back and forth.
--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber
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