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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Thu Mar 22, 2012 5:18 am Post subject: Stobes

Here's more work for Bob to do in his "free" time.



I have seen many questions on how to quiet strobes and would like to make the following observation:



Having a central strobe power pack and running long wires to the wingtips (or to the rim of your flying saucer) is a recipe for RFI/EMI. A much more sensible design is to have the capacitors and trigger coil, located at the strobe tube. Strobe synchronization is simple to achieve. Noise would be gone.



Whelen actually makes remote power packs, but at a price that is affordable only to Wall Street hedge fund managers. So a DIY version of a lighter weight "distributed" replacement for the standard Whelen strobe power pack would be a good solution to noise. Estimated weight savings 2 pounds. Not trivial.  



I have designed  LED strobes in this fashion. Only position-light power wiring to the wingtip is required. This design merely pulses the synchronization to fire the strobes.

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 22, 2012 11:05 am Post subject: Stobes

At 08:18 AM 3/22/2012, you wrote:

 	  Quote: 	
		  



Here's more work for Bob to do in his "free" time.



I have seen many questions on how to quiet strobes and would like to 

make the following observation:



Having a central strobe power pack and running long wires to the 

wingtips (or to the rim of your flying saucer) is a recipe for 

RFI/EMI. A much more sensible design is to have the capacitors and 

trigger coil, located at the strobe tube. Strobe synchronization is 

simple to achieve. Noise would be gone.


	


    As you've noted, there are several designs qualified

    for TC aircraft where the power conditioning is adjacent

    to the strobe tube. But I would offer that centralized

    supplies are also qualified, i.e. have passed DO-160

    conducted and radiated emissions. So if installed with

    attention to good practice for treatment of shields,

    they should present no greater noise problem in an

    OBAM aircraft than they do in a TC aircraft.

 	  Quote: 	
		  Whelen actually makes remote power packs, but at a price that is 

affordable only to Wall Street hedge fund managers. So a DIY version 

of a lighter weight "distributed" replacement for the standard 

Whelen strobe power pack would be a good solution to noise. 

Estimated weight savings 2 pounds. Not trivial.


	


    Those are slick . . . but they're a relatively low

    volume product in comparison with the central supply

    configuration and they take up more room in what

    might be a more crowded space. Hence the higher cost

    that is not well tolerated in the SE propeller driven

    market.



    All the strobes on turbine aircraft have local power

    supplies but as you've noted, these are breathtakingly

    expensive.

 	  Quote: 	
		  I have designed  LED strobes in this fashion. Only position-light 

power wiring to the wingtip is required. This design merely pulses 

the synchronization to fire the strobes.


	


    What kind of voltages/currents and duty cycles

    are involved? I've seen some LED anti-collision

    protects offered to HBC while I was still there but

    folks who showed them to me were unable or reluctant

    to discuss design details.



    What's the architecture for wiring up large arrays

    of LED's. The tail strobe I saw had about 36 leds

    in it. The guy thought it was 4 strings of 9 each.

    At 4 volts per led in an overdriven pulse mode,

    one comes to believe that a pulsed, 36 volt constant

    current supply is used. What approach has been most

    attractive in your experience?



    EMC issues for these supplies is a bit simpler. There's

    little probability of 'output noise' due to flashing

    and the operating frequency of the switchmode power

    supply is generally much higher . . . hence easier

    to filter . . . assuming the designer recognizes

    the need for a filter. We discovered this lower

    level design goal in the Luxeon power supplies that

    folks have been using in their wingtips. I've sold

    perhaps 50 filtered supplies over the past 4-5 years

    and perhaps half that number of filter boards for

    folks who already had supply modules.

   Bob . . .

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stearman456

Joined: 14 Aug 2010
Posts: 49

Posted: Fri Mar 23, 2012 4:05 am Post subject: Re: Stobes

What is the advantage to having local power supplies for your strobe lights vs a single, central, power supply - or vice versa?  The two strobe systems I'm considering are identical (lights, output) apart from three power supplies vs one.



Dan

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email(at)jaredyates.com
Guest

Posted: Fri Mar 23, 2012 8:17 am Post subject: Stobes

The remote units are likely going to be a heavier installation, and they will require some sort of mechanism for synchronization if there is to be any.



On Fri, Mar 23, 2012 at 8:05 AM, stearman456 <warbirds(at)shaw.ca (warbirds(at)shaw.ca)> wrote:

 [quote]--> AeroElectric-List message posted by: "stearman456" <warbirds(at)shaw.ca (warbirds(at)shaw.ca)>

  

 What is the advantage to having local power supplies for your strobe lights vs a single, central,power supply - or vice versa?  The two strobe systems I'm considering are identical (lights, output) apart from three power supplies vs one.

  

 Dan

 

 

 

 

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tperry(at)lvtofly.com
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Posted: Fri Mar 23, 2012 11:41 am Post subject: Stobes

Advantage is less noise from the high voltage lines running the length of your airplane.   Also your strobes are independent of one another, if you loose one power supply your other strobes still work.  



Tim Perry



On Mar 23, 2012, at 12:16 PM, Jared Yates <email(at)jaredyates.com> wrote:



[quote] The remote units are likely going to be a heavier installation, and they will require some sort of mechanism for synchronization if there is to be any

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stearman456

Joined: 14 Aug 2010
Posts: 49

Posted: Sat Mar 24, 2012 4:02 am Post subject: Re: Stobes

 	  tperry(at)lvtofly.com wrote: 	
		  Advantage is less noise from the high voltage lines running the length of your airplane.   Also your strobes are independent of one another, if you loose one power supply your other strobes still work.  	




That makes sense - the kit with the three power supplies is slightly more expensive but I can afford the weight of the extra units. Flying an airplane with noisy strobes has always driven me nuts in the past.  



Any advice on building the ultimate in quiet strobe installations (Whelen A 490A,TS,CF Power Supplies) appreciated.



Dan

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Eric M. Jones

Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts

Posted: Sat Mar 24, 2012 6:01 am Post subject: Re: Stobes

Bob N. saiys:  	  Quote: 	
		  I would offer that centralized 

supplies are also qualified, i.e. have passed DO-160 

conducted and radiated emissions. So if installed with 

attention to good practice for treatment of shields, 

they should present no greater noise problem in an 

OBAM aircraft than they do in a TC aircraft. 	




I agree Bob, but the basic EMC rule of fixing the noise at its source is a good one, and this points in the direction of putting the HV very close to the strobe tubes. If a standard installation works well, that does not mean a global shift in design is unwise, particularly if some particular design has problems.



Bob N. says:  	  Quote: 	
		  All the strobes on turbine aircraft have local power 

supplies but as you've noted, these are breathtakingly 

expensive. 	




This is interesting Bob. I wonder if there are some additional design forces at work here?



 	  Quote: 	
		  What kind of voltages/currents and duty cycles 

are involved? I've seen some LED anti-collision 

protects offered to HBC while I was still there but 

folks who showed them to me were unable or reluctant 

to discuss design details. 



What's the architecture for wiring up large arrays 

of LED's. The tail strobe I saw had about 36 leds 

in it. The guy thought it was 4 strings of 9 each. 

At 4 volts per led in an overdriven pulse mode, 

one comes to believe that a pulsed, 36 volt constant 

current supply is used. What approach has been most 

attractive in your experience? 	




Bob, I try to stay away from boosted switch-mode LED supplies of any sort. The reason for these (one presumes) is that common lighting is often in strings that make difficult parallel wiring, or that parallel lights demand higher currents, which in some instances is difficult to achieve. But having only 12-28 voltage "Luminaries" allows designs of large parallelism. But this is simple on a PCB. My discontinued (but fabulous)  LED position light was 4 strings of 3 (70 mA) LEDs. My LED tail light is a single beefy 1200 mA LED with a linear LM317 regulator. Totally EMC silent.* 



 	  Quote: 	
		   I've sold perhaps 50 filtered supplies over the past 4-5 years 

and perhaps half that number of filter boards for 

folks who already had supply modules. 

Bob . . . 	




*As an aside. These supplies were Luxdrive Power Pucks (I don't think Luxeon is involved). You are to be congratulated on quieting these demons. I gave up and dissolved away the potting to examine the PCB. The design was quite clearly laid out by someone who had never taken a Kimmel Gerke course. I toyed with the notion of redesigning the device, but finally sold my shelf full of them on Ebay, converted all my designs to linears, and washed my hands of it.



Some data and comments:



The Whelen  strobe anti-collision power supply output nominal is 550V. This fact alone would make distributed supplies a good design choice. Separate supplies at the tubes should theoretically weigh less if the supporting structure and wiring is included, but the comparison is hard to glean from the published Whelen data. Whelen has one spearate strobe supply that says "cannot be synchronized", which is weird when you understand how little it takes to do so.



My "vapor-ware" design uses a parallel string of two RED leds. Oddly, the FAA has had a long love affair with neon tubes since the 1930s, so red is a permissible color and red LEDs have the highest efficiency. (But the human visual response is best at 555 nm yellow green...the color under the African jungle canopy). Xenon blue-white strobes are easy to make. (A side note for your kid's science project...Radon should make great flash tubes..unfortunately all radon isotopes are radioactive.) 



But I digress.... My design uses an array of red LEDs for 12V, and a parallel array of 4 for 28V. powered by small local supercaps (hey, why not?). Each LED "strobe lamp" is basically pulsed on and off and synchronized by a central circuit the size of a postage stamp. The power to the LED strobes is the same as the position lights.



I would gladly publish the circuit but it is incomplete...as is my Glastar, which I'd better start working on. My electro-whizzie work has slowed down since I spend much of my time selling switch guards. NASCAR is also a big market. See attached. (The Redbull team was so secret at first I thought they had to be spooks!)

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_________________
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net

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