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Shielded wire for LED strobe?

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dalemed

Joined: 25 Dec 2007
Posts: 46

Posted: Wed Sep 02, 2009 12:55 pm Post subject: Shielded wire for LED strobe?

I'm in the process of installing an AveoFlash combination LED position light and strobe.  I'm getting mixed signals on whether or not I should use shielded wire on the strobe line.



Most "experts" say that shielding won't help because if there's a problem its conducted, not radiated.  Initially, the factory said shielded wire isn't needed but they later came back and said that there are grounding issues with Zenith airplanes and therefore I should use shielded wire.



I've asked them how the shield connection should be done. Do both ends need to be attached to the airframe or just one end?  If one, which end?



Does anyone have experience with the Aveoflash strobe?  



Thanks!

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_________________
Dale
Zenith Zodiac CH650

psm(at)att.net
Guest

Posted: Wed Sep 02, 2009 1:14 pm Post subject: Shielded wire for LED strobe?

Hi Dale,



I don't have experience with those units, but I was an electrical 

engineer for more years than I have fingers.  Let me try to clear up 

the shielding and grounding issue.



There are two different wired connections in a strobe unit.  One is 

the 12 volt DC power wiring that goes from the battery to the strobe 

power supply.  The other goes from the strobe box to the flash tube 

mounted on the wing.



The regular 12 volt power wire probably doesn't need any special 

attention.  The ground path completing the circuit from the strobe 

box to the battery must be at least as big as the power wire, but 

this isn't a difficult thing to do with either wire or the metal skin 

of the plane.  You should include a switch and fuse or circuit 

breaker in this power circuit - just like any other device on the plane.



The wire from the box to the flash tube is a different kettle of 

fish.  It has high voltage (thousands of volts) and switches 

completely on and off as often as the tube lights up - possibly a lot 

more if it has an A/C signal.  This path should be kept as short as 

possible and probably shielded with one of two methods.  Either it 

should be shielded wire or twisted pair wire should be used between 

the tube and the box.  There will be two wires going to the tube - 

these are the ones to twist.  The problem is different if you have a 

central power supply for the tubes and long high voltage lines or 

separate supplies mounted near the flash tubes.  In my plane (XL with 

Zenith supplied strobes) the power supply is mounted in the wing tip 

and the high voltage wires are only a foot or two long.  Even if 

these are not twisted the wing skin will shield the RF noise anyway.



All of this assumes you have  a good electrical connection from the 

wing skin to the fuselage.  This will happen automatically if you 

don't insulate all the metal to metal joints with zinc chromate or 

some other paint.  If you do that then just include some bonding 

wires (usually braided copper) between the big wing and fuselage 

parts to make a solid electrical connection.  I recommend you do this 

whether you use the skin as a ground for the strobes or not.



Good luck,



Paul

XL awaiting engineering changes.



At 01:55 PM 9/2/2009, you wrote:

 	  Quote: 	
		  I'm in the process of installing an AveoFlash combination LED 

position light and strobe.  I'm getting mixed signals on whether or 

not I should use shielded wire on the strobe line.



Most "experts" say that shielding won't help because if there's a 

problem its conducted, not radiated.  Initially, the factory said 

shielded wire isn't needed but they later came back and said that 

there are grounding issues with Zenith airplanes and therefore I 

should use shielded wire.



I've asked them how the shield connection should be done. Do both 

ends need to be attached to the airframe or just one end?  If one, which end?



Does anyone have experience with the Aveoflash strobe?



Thanks!



--------

Dale

Flying Cessna 170B

Building Zenith CH650

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carlossa52(at)gmail.com
Guest

Posted: Wed Sep 02, 2009 2:25 pm Post subject: Shielded wire for LED strobe?

Hey, Paul, didn't you miss the point of the question?

(If you didn't then I did...)



My interpretation:

The Aveo strobe is solid state based, so there is no high voltage at all - therefore the question is, does one STILL need shielding, given the low power of this type of strobe?

 

Cheers

Carlos

2009/9/2 Paul Mulwitz <psm(at)att.net (psm(at)att.net)>

[quote] --> Zenith601-List message posted by: Paul Mulwitz <psm(at)att.net (psm(at)att.net)>

 

 Hi Dale,

 

 I don't have experience with those units, but I was an electrical engineer for more years than I have fingers.  Let me try to clear up the shielding and grounding issue.

 

 There are two different wired connections in a strobe unit.  One is the 12 volt DC power wiring that goes from the battery to the strobe power supply.  The other goes from the strobe box to the flash tube mounted on the wing.

  

 The regular 12 volt power wire probably doesn't need any special attention.  The ground path completing the circuit from the strobe box to the battery must be at least as big as the power wire, but this isn't a difficult thing to do with either wire or the metal skin of the plane.  You should include a switch and fuse or circuit breaker in this power circuit - just like any other device on the plane.

  

 The wire from the box to the flash tube is a different kettle of fish.  It has high voltage (thousands of volts) and switches completely on and off as often as the tube lights up - possibly a lot more if it has an A/C signal.  This path should be kept as short as possible and probably shielded with one of two methods.  Either it should be shielded wire or twisted pair wire should be used between the tube and the box.  There will be two wires going to the tube - these are the ones to twist.  The problem is different if you have a central power supply for the tubes and long high voltage lines or separate supplies mounted near the flash tubes.  In my plane (XL with Zenith supplied strobes) the power supply is mounted in the wing tip and the high voltage wires are only a foot or two long.  Even if these are not twisted the wing skin will shield the RF noise anyway.

  

 All of this assumes you have  a good electrical connection from the wing skin to the fuselage.  This will happen automatically if you don't insulate all the metal to metal joints with zinc chromate or some other paint.  If you do that then just include some bonding wires (usually braided copper) between the big wing and fuselage parts to make a solid electrical connection.  I recommend you do this whether you use the skin as a ground for the strobes or not.

  

 Good luck,

 

 Paul

 XL awaiting engineering changes.



[b]

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z601a(at)anemicaardvark.c
Guest

Posted: Wed Sep 02, 2009 2:55 pm Post subject: Shielded wire for LED strobe?

On Wednesday 02 September 2009 15:55, dalemed wrote:

 	  Quote: 	
		   



 I'm in the process of installing an AveoFlash combination LED position

 light and strobe.  I'm getting mixed signals on whether or not I should use

 shielded wire on the strobe line.



 Most "experts" say that shielding won't help because if there's a problem

 its conducted, not radiated.  Initially, the factory said shielded wire

 isn't needed but they later came back and said that there are grounding

 issues with Zenith airplanes and therefore I should use shielded wire.



 I've asked them how the shield connection should be done. Do both ends need

 to be attached to the airframe or just one end?  If one, which end?


	


A shield should be used as exactly that: a shield. It should not be used to 

carry current. You should have a separate ground wire (unless, of course,  

you are using the airframe as as a current-carrying ground for the strobe). 



If I were wiring this, I would (assuming it is possible) not connect the 

strobe assembly to the aircraft frame electrically. I would connect the 

strobe power supply to the airframe, and run a separate, current carrying 

ground wire out to the strobe, not connected to the airframe at the strobe 

end. I would carry the strobe signal on a shielded cable, with the shield 

connected to the strobe power supply at the strobe power supply, and nowhere 

else. 



Failing to do this can create a ground loop. Grounding the shield at both ends 

causes it to carry current, and fail to act as a shield.



-- 

=============================================

                Do not archive.

=============================================

                Jim B Belcher

    BS, MS Physics, Math, Computer Science

                  A&P/IA

     Retired aerospace technical manager

=============================================

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tigerrick(at)mindspring.c
Guest

Posted: Wed Sep 02, 2009 4:09 pm Post subject: Shielded wire for LED strobe?

Hi, Dale.  I'm reasonably familiar with the AveoFlash units, since we sell Aveo products at my shop.



The beauty of these units is that the "power supply" (such as it is), is molded into the wingtip unit itself. All you need to do is ground the units to the airframe with the black wire, provide power (red wire = nav lights, yellow = strobe), and connect the blue wires to each other if your want the strobes to be synchronized. If you're nervous about having a good electrical ground through your airframe, you could always run another conductor out to the wingtips from the battery ground, but I can't imagine this really being necessary on any metal Zenith that has good electrical continuity through the airframe.



When compared to traditional strobe power supplies that send high voltage pulses to a xenon flash tube from a multivibrator type power supply, there's virtually no RF interference generated by the Aveo units. However, if you were to mount a wingtip or beacon unit right next door to your comm antenna or a microphone cable, you might pick up some noise from the internal flash power supply. These units use so little current and are so voltage tolerant that the amount of spurious RF energy generated is damn little.  But you might be able to induce a bit into an antenna or mic cable if you really tried by putting the cable very close to the base of the Aveo unit.



I just went out to the shop with my handheld and performed a little experiment. With both the strobes firing and the nav lights on, and tuned to the local tower freq, I could only pick up radiated noise (that coincided with the strobe pulse) when the handheld's whip antenna was within an inch of the base of the AveoFlash unit (where the circuit board dwells), or when the antenna was wrapped up in the power leads. It wouldn't break squelch on its own, but you can hear a faint "swish swish swish" in the background of other tower transmissions.



When the antenna was moved a foot or more away, I could no longer detect any interference.



Hardly scientific, I know, but it suggests that the RF noise generated is very minor and might only be an issue if you had your comm antenna mounted very close to the AveoFlash unit itself. Do you have any antennas in composite wingtips? Or an Aveo fuselage beacon near an antenna? I can't think of other scenarios where it would be an issue, other than very near a mic cable or power lead to an intercom or audio panel. But running a shielded power cable certainly wont hurt anything. If you ground only one end of the shield, it should be the one closest to battery ground.



Just my $0.02. Hope it helps.



Rick Lindstrom

ZenVair N42KP



--

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psm(at)att.net
Guest

Posted: Wed Sep 02, 2009 4:44 pm Post subject: Shielded wire for LED strobe?

Hi Carlos,



Apparently I did miss the point.  If the device in question is just a 

bunch of LEDs powered by 12 volts then it seems unlikely that any 

special actions will be needed to prevent noise in the radio 

receiver.  If anything is needed, a small filter on the power leads 

at the device would probably do just fine.  It could be as simple as 

a small ceramic capacitor - probably 50 cents at Radio Shack.



It all depends on whether the primary light "Bulb" is a flash tube or not.



Best regards,



Paul



At 03:18 PM 9/2/2009, you wrote:

 	  Quote: 	
		  Hey, Paul, didn't you miss the point of the question?

(If you didn't then I did...)



My interpretation:

The Aveo strobe is solid state based, so there is no high voltage at 

all - therefore the question is, does one STILL need shielding, 

given the low power of this type of strobe?



Cheers

Carlos

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dalemed

Joined: 25 Dec 2007
Posts: 46

Posted: Wed Sep 02, 2009 5:42 pm Post subject: Re: Shielded wire for LED strobe?

Thank you all very much!



Since the factory is recommending shielded wire (probably just CYA) and because I have some, I'll just tolerate the added few ounces.  The factory, like Rick, suggested connecting the shield as close to the battery negative as possible.

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_________________
Dale
Zenith Zodiac CH650

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