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03-03-2014, 06:56 AM
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Join Date: Dec 2004
Location: Gold Hill, NC25
Posts: 2,400
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Im afraid you will be chasing noise with these and may never get enough bandaids to ever correct the problem. The reason your getting the noise can be found here in my FAQ on LED lights.
__________________
Kahuna
6A, S8 ,
Gold Hill, NC25
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03-03-2014, 08:40 AM
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Join Date: Aug 2007
Location: Boise, Idaho
Posts: 468
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Quote:
Originally Posted by Kahuna
Im afraid you will be chasing noise with these and may never get enough bandaids to ever correct the problem. The reason your getting the noise can be found here in my FAQ on LED lights.
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The statements about RF noise and LEDs is actually not entirely correct. It is possible to design switching supplies that don't emit RFI. It is however not a simple task, and it does require that the design be carefully implemented such that RF noise is not created in the switching circuit, as it is true that suppression once you have a noise source is difficult and inconsistent. The key is to create a switcher that does not have RF frequency resonances in the switch-mode loop, and that requires a combination of careful layout of the circuit, and selection of components in the design. AeroLEDs initially ran into some RF issues with some of our nav/strobe products, but we have worked through the design and have identified the root cause of the issue, and have identified and implemented design changes to solve the problem. We have made an investment in RF test equipment that allows us to measure emissions, and that gave us the tools we needed to engineer the products that we make to be free of RF noise.
The advantage of a linear regulator is that is is not prone to RF noise, but the disadvantage is that it is is not as power efficient as a switcher, and has a limited voltage range of operation so you have to have voltage specific part numbers.
Dean Wilkinson
CTO, AeroLEDs LLC
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03-03-2014, 08:57 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by Kahuna
Im afraid you will be chasing noise with these and may never get enough bandaids to ever correct the problem...
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...Except that I can get 3 out of 4 to run dead silent...
If they were all screaming, I might be more discouraged.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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03-03-2014, 10:21 AM
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Join Date: Jul 2005
Posts: 1,346
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Quote:
Originally Posted by Dean_aeroleds
The statements about RF noise and LEDs is actually not entirely correct. It is possible to design switching supplies that don't emit RFI. It is however not a simple task, and it does require that the design be carefully implemented such that RF noise is not created in the switching circuit, as it is true that suppression once you have a noise source is difficult and inconsistent.
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What Dean said. I design circuits all the time with switchers that have to pass DO-160G Sec 22 cat H and P, and/or MIL-STD-461 RE102-external radiated emissions (and CE). Not that hard, but someone designing for a handheld consumer flashlight is not going to pay a lot of attention to emissions in their design.
__________________
Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS, L3 Lynx NGT-9000
N164WM
N184WM reserved (RV-8)....finishing kit in progress. Titan IOX-370
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03-05-2014, 09:09 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Based upon my experiments with a handheld radio, it appears that my "problem child" light is throwing RFI out into the world, rather than through the wiring. Since the body of the light is aluminum and grounded to the airframe, then the only escape path is through the lens aperture.... I guess its worth a shot to place a conductive screen (faraday cage) across the lens and ground it to the airframe. Anyone see a problem with this approach?
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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03-05-2014, 10:35 PM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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Quote:
Originally Posted by Toobuilder
Based upon my experiments with a handheld radio, it appears that my "problem child" light is throwing RFI out into the world, rather than through the wiring. Since the body of the light is aluminum and grounded to the airframe, then the only escape path is through the lens aperture.... I guess its worth a shot to place a conductive screen (faraday cage) across the lens and ground it to the airframe. Anyone see a problem with this approach?
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I would be very interested in your result and how you make that.
In my experiment with these lights (I have two Trustfire 11000LM) one is dead silent and one puts out a bit of noise. Over the last few days, I ran a shielded wire for the positive side and another wire to my ground buss instead of using the airframe. I had been hoping this will make it all the better but unfortunately no change. I have looked at the guts of these lights and they are the same, not sure why one is noisy but the other one is not.
Keep us posted on your results.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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03-06-2014, 07:15 AM
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Join Date: Aug 2007
Location: Ontario, Canada
Posts: 2,291
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Mehrdad - one of the more common methods of shielding display surfaces is by coating the glass with a thin layer of indium-tin-oxide (ITO). This provides a conductive surface which, if deposited thinly, has very little effect on transmissivity of the glass at light frequencies.
With respect to where the RF energy is being squirted out of the lights, unless you seal the open battery end of the light, one can rest assured that gaping hole will likewise be a large source of emissions. Keep in mind there are two categories of emissions, conducted (as in conducted along the wires) and radiated (as in squirting from the unit into free space). We are without doubt seeing both types with these lights.
The best fix would be to install a machined end cap on the battery compartment, and that end cap would contain a coaxial filter capacitor for the input power lead. Inside the battery compartment an LC network would be used as additional filtering. Granted, filtering isn't as effective as making the initial switching power supply quiet by design, but filtering is the only real option available on these wee beasts.
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03-06-2014, 09:24 AM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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Quote:
Originally Posted by Canadian_JOY
Mehrdad - one of the more common methods of shielding display surfaces is by coating the glass with a thin layer of indium-tin-oxide (ITO). This provides a conductive surface which, if deposited thinly, has very little effect on transmissivity of the glass at light frequencies.
With respect to where the RF energy is being squirted out of the lights, unless you seal the open battery end of the light, one can rest assured that gaping hole will likewise be a large source of emissions. Keep in mind there are two categories of emissions, conducted (as in conducted along the wires) and radiated (as in squirting from the unit into free space). We are without doubt seeing both types with these lights.
The best fix would be to install a machined end cap on the battery compartment, and that end cap would contain a coaxial filter capacitor for the input power lead. Inside the battery compartment an LC network would be used as additional filtering. Granted, filtering isn't as effective as making the initial switching power supply quiet by design, but filtering is the only real option available on these wee beasts.
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Canadian_JOY,
Thanks for the info. After reading your post, I started looking at transparent ITO film/glass and learned a bit more about it. I am planning on testing this by covering the front and back portion of the light with some aluminum wraps to see if it has any effect on the noise. If that proves successful, then I will try the ITO on the lens.
The back side (battery side) of my light is open and that would be an easy fix which I will try it in the next couple of days and will report back.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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03-06-2014, 11:48 AM
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Join Date: Oct 2007
Location: Sherrills Ford, NC (Lake norman area)
Posts: 432
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standing by
Mehrdad
just waiting to here how you do and then I may purchase a couple of these lights. Please keep us advised on your noise smack-down.
__________________
Bill Fearheiley
Lake Norman, NC (14A)
RV7a N705RP (no longer own)
Contribution in for 2017, money well spent
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03-06-2014, 12:33 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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As I understand a Faraday cage (not much), we really only need to seal the enclosure at the frequency we're using. So yes, there is likely RF spewing out the back of the battery tube, but if we seal it off "enough" to stop the RF from escaping, we're good.
...As I type this, I see it's probably a lot easier to block our radio transmissions from getting in than keeping the noise from getting out. The size of the aperature (holes in the screen) are pretty big to effectively contain radio transmissions, but the wavelength of the noise may be a lot smaller... May end up with something really small like the screen used in the door of a microwave oven.
__________________
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
______________
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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