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Electrical Noise Prevention

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messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Fri Jul 16, 2010 8:20 pm Post subject: Electrical Noise Prevention

Hi!



I'm finishing up my electrical wiring and am wondering about noise. I'm not sure what types there are, nor do I know all the sources. I have heard the alternator and the transmitting radio can cause problems. Also heard that anything with a pulsing signal could also be a source. 



I have a 3 or 4  100-150 Mhz ferrite RF suppressors from MGL http://www.mglavionics.com/EMI_suppressor_for_VHF_frequencies.pdf.  It sounds like MGL recommends putting them on any output from the radio, but not the antenna.  



I've heard that twisting the feeder line to the noise maker with it's ground coming back from the device (or having the wires next to each other) will help cancel out EMF generated noise. 



My schematic is posted in another thread: http://www.matronics.com/forums/viewtopic.php?t=72713. The two alternator leads are about 1' long and are wrapped together until one separates to go to the regulator and the other to the alt disconnect relay, which is right next to the regulator. The regulator output wire goes ~6" to a 10k micro (10 mili?) F 50V filter capacitor. 



I forgot to label the left and right mag wires, which are dangling out the bottom center of the pic. The engine instruments will be 6 cht's, 6 egt's, fuel pressure sender, fuel flow sensor, OT, OP, carb temp, and tach. All these will plug into the RDAC above the battery. A shielded data cable goes from there back to the EFIS.



All the wires go through the firewall in either of two firewall penetations, then join together going to the right side, then back to the instrument panel and into a wire wrap along a light channel 'tray' along the bottom of the instrument panel. The pic shows the panel rotated 90 degrees in the open position.



Most of the wires hanging loose are grounds. They'll be bundled together in the final installation, and if needed, close to the panel feed wires already wrapped. Besides the mag wires (which are shielded), the only wire with pusling would be the boost pump. The radio (which may be a handheld) and strobe/nav/pos lights are not in. I know strobes are notorious noise makers. I have the shielded cable installed already in the wings.



How does this look to you? Thanks again for taking your time helping me

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_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Jul 17, 2010 2:11 pm Post subject: Electrical Noise Prevention

At 11:20 PM 7/16/2010, you wrote:

 	  Quote: 	
		  



Hi!



I'm finishing up my electrical wiring and am wondering about noise. 

I'm not sure what types there are, nor do I know all the sources. I 

have heard the alternator and the transmitting radio can cause 

problems. Also heard that anything with a pulsing signal could also 

be a source.

  <snip>
	




 	  Quote: 	
		  How does this look to you? Thanks again for taking your time helping me 


	


    Suppliers of product to the TC aircraft world

    are encouraged if not commanded to worship

    at that altars of the gods of blissful

    system integration.  Catechisms for these

    orders are documented in RTCA DO-160,

    Mil-Std-810, Mil-Std-704 just to name the

    most prevalent.



    By the time the system integrator is tasked

    with finding a place to bolt it in and wire

    it up to make it work, 99.99% of concerns

    for unhappy experience are already addressed.



    Even when the hardware has not been admitted

    to the social A-List for the aviation community,

    the risks for noise issues are relatively low.

    A single point ground for all the instrument

    panel mounted goodies and paying attention

    to the manufacturer's installation instructions

    goes a long way to crafting a noise free future.



    Ferrite beads are found useful only when the

    original designer of a potential noise

    antagonist/victim didn't do their homework.

    To assume that they would be useful before you've

    identified a real noise issue is probably not

    a good use of time . . . Fly the airplane

    first . . . the ferrites can probably

    be willed to the neighbor kid as slingshot

    ammo.



    Bob . . .

 	  Quote: 	
		  --------

Dan





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=305153#305153





Attachments:



http://forums.matronics.com//files/cabin_wiring_labeled_836.jpg

http://forums.matronics.com//files/firewall_electrical_components_labeled_828.jpg



Checked by AVG - www.avg.com

07/17/10 01:35:00


	




   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Sun Jul 18, 2010 5:08 am Post subject: Re: Electrical Noise Prevention

Thanks, Bob

_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Jul 18, 2010 7:52 am Post subject: Electrical Noise Prevention

At 11:20 PM 7/16/2010, you wrote:

 	  Quote: 	
		  




	


  <snip>



 	  Quote: 	
		  How does this look to you? Thanks again for taking your time helping me 

http://forums.matronics.com//files/cabin_wiring_labeled_836.jpg


	


   In this picture you show a "main bus" . . . what is this?

   Normally, the main bus is a contiguous connection by means

   of unbroken bar or strip to the power feed side of an array

   of breakers or fuses. I.e., this component is already in existence

   inside a fuse block . . . or is fabricated and configured

   like the bus bars in this photo:



http://aeroelectric.com/Pictures/Breakers/Breaker_Panel_Busing_1.jpg



   You also show a panel ground that appears to be on

   the side of the fuselage. Is this a floating tie point

   for the collection of all ground wires off the panel mounted

   accessories? In the various z-figures, I suggest a gathering

   of the grounds on what's called a "panel" or "avionics ground

   bus". This is intended to offer a single point ground for a fist full

   of wires and centrally located to the serviced accessories

   (on the panel itself). Further, it is NOT grounded to the

   panel structure . . . but serves as a handy way to extend

   lots of grounds to the fire wall ground in fewer wires. For

   a panel ground, you'd need something like:



http://aeroelectric.com/Pictures/Grounding/Avionics_Bus_3.jpg



   and wired like:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8Q.pdf



   where I show 5 strands of 20AWG running from the panel ground

   to the fire wall ground. This provides redundant, low resistance

   connection (roughly 2 mOhms/Ft equal to 13AWG) between the

   two busses. The 5 strands and panel ground provides a much

   handier way to deal with grounds on the panel mounted

   accessories.

   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Sun Jul 18, 2010 10:41 am Post subject: Re: Electrical Noise Prevention

 	  Quote: 	
		  In this picture you show a "main bus" . . . what is this? 	




This is a fuse block fed by a 10awg line from the battery contactor. I had incorrectly called it a 'bus'. Now I know better.

 	  Quote: 	
		  You also show a panel ground that appears to be on 

the side of the fuselage. Is this a floating tie point 

for the collection of all ground wires off the panel mounted 

accessories? 	




The panel ground is made of a section of 'forest of tabs'. I took one 48 tab forest and cut it into 3 pieces. One is on the hot side of the firewall and is connected to another section on the cool side via a 5/16" SS bolt. I forget the exact numbers, but when I measured the resistance of the SS, it was only slightly higher than brass. I chose SS because of its higher melting point.



A 10awg ground goes from the inside firewall ground to another section of tab forest for the panel ground. The panel ground is on the outside (lower side) of the cover to the main fuse block a few inches from the side of the fuselage. The cover will be piano hinged to the underside of the glareshield. In the pics, the glareshield is removed, so I've used a bent piece of metal to put the blocks in about the same position.



Next step is to wrap all the wires together in a spiral wrap starting from where teh bundle enters the tray on the right side of the fuselage. Feeders and grounds will branch off where shown.

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_________________
Dan

tim2542(at)sbcglobal.net
Guest

Posted: Sun Jul 18, 2010 5:29 pm Post subject: Electrical Noise Prevention

Hi Bob and thanks for the help. 

I am trying to understand your comment re: grounds below. Why is the 5X20

AWG better than a single large wire? And why separate panel and avionics

grounds? In my case I had planned either a DB 25 or forest of tabs approach

on the front of the (glass) panel with all local ground needs tied in there,

then a suitable ground run back to the battery. With a rear mounted battery

do you then recommend the 5X20AWG run all the way to the back?

For reference I am building an all electric COZY.

Thanks, Tim Andres



 



   I suggest a gathering

   of the grounds on what's called a "panel" or "avionics ground

   bus". This is intended to offer a single point ground for a fist full

   of wires and centrally located to the serviced accessories

   (on the panel itself). Further, it is NOT grounded to the

   panel structure . . . but serves as a handy way to extend

   lots of grounds to the fire wall ground in fewer wires. For

   a panel ground, you'd need something like:



http://aeroelectric.com/Pictures/Grounding/Avionics_Bus_3.jpg



   and wired like:



http://www.aeroelectric.com/PPS/Adobe_Architecture_Pdfs/Z13-8Q.pdf



   where I show 5 strands of 20AWG running from the panel ground

   to the fire wall ground. This provides redundant, low resistance

   connection (roughly 2 mOhms/Ft equal to 13AWG) between the

   two busses. The 5 strands and panel ground provides a much

   handier way to deal with grounds on the panel mounted

   accessories.

   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Mon Jul 19, 2010 5:45 am Post subject: Re: Electrical Noise Prevention

 	  Quote: 	
		   5 strands of 20AWG running from the panel ground 

to the fire wall ground. 	




Good question, Tim. 



I had missed that point. I have a single 10awg wire going from my panel ground to the firewall, not 5 smaller ones. I used 10awg for my main feeder, so chose the same size for the ground.

_________________
Dan

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jul 19, 2010 11:48 am Post subject: Electrical Noise Prevention

At 08:25 PM 7/18/2010, you wrote:

 	  Quote: 	
		  



Hi Bob and thanks for the help.

I am trying to understand your comment re: grounds below. Why is the 5X20

AWG better than a single large wire?


	


       Single wire is single point of failure . . . although

       it can also be argued that 5 parallel paths offers the

       POTENTIAL for an undetected, latent failure. Further,

       at higher frequencies, multiple parallel strands are

       lower impedance connection than a single strand (or

       one thin, wide strap would be good too). The most

       compelling reason was to offer a high probability

       for installation success . . . the D-sub connector

       accepts 20AWG wires. Going with a single, larger

       conductor leaves it up to the installer to fabricate

       the joint between the ground wire and the avionics

       ground bus.



       The short answer is "no single reason . . . but

       several significant reasons". But those reasons

       are rooted in the features of a D-sub based

       ground bus. Other configurations change the

       selection of ingredients that go into YOUR

       recipe for success.

 	  Quote: 	
		  And why separate panel and avionics grounds?


	


      Sorry about the vague vernacular. For the purposes

      of this discussion, let's use Figure Z15, View B

      and move the battery from the nose back to the

      rear spar and ground it to the firewall ground

      stud. An avionics ground is on the panel sheet

      and intended to bring small power/signal wires

      to a common ground. The "panel" ground is captive

      to the airplane and would take care of grounding

      airframe accessories not generally associated with

      music, bells, lights and pointers.



 	  Quote: 	
		    In my case I had planned either a DB 25 or forest of tabs approach

on the front of the (glass) panel with all local ground needs tied in there,

then a suitable ground run back to the battery. With a rear mounted battery

do you then recommend the 5X20AWG run all the way to the back?


	


     The 5x20 configuration presumes a tractor airplane with a forest-of-tabs

     on one or both sides of firewall.



 	  Quote: 	
		  For reference I am building an all electric COZY.


	


     Okay, where are your panel equipment power distribution

     busses located? How about doing a sketch on where the

     power and ground busses are located along with a list

     of loads on each bus.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Jul 19, 2010 11:48 am Post subject: Electrical Noise Prevention

At 08:45 AM 7/19/2010, you wrote:

 	  Quote: 	

 >  5 strands of 20AWG running from the panel ground

 > to the fire wall ground.

Good question, Tim.

I had missed that point. I have a single 10awg wire going from my 

panel ground to the firewall, not 5 smaller ones. I used 10awg for 

my main feeder, so chose the same size for the ground.

   Since you're not using a d-sub avionics ground, leave

   the 10AWG in place.

   Bob . . .

tim2542(at)sbcglobal.net
Guest

Posted: Mon Jul 19, 2010 1:55 pm Post subject: Electrical Noise Prevention

Thanks Bob! That makes sense especially when using the D sub. 

In my case the fuse blocks will probably be under the Right seat, about a

30" run up to the avionics and various switches. I'm looking into using a

swing down panel to hold the fuse blocks under the panel, but it looks

complicated. There will be 5 breakers in the panel as well. The ground bus

will be in front of the panel in an undetermined location but close to the

avionics stack.

I'm still working on the drawing and will post it soon.



 

 	  Quote: 	
		  For reference I am building an all electric COZY.


	


     Okay, where are your panel equipment power distribution

     busses located? How about doing a sketch on where the

     power and ground busses are located along with a list

     of loads on each bus.



   Bob . . .

messydeer

Joined: 13 Feb 2006
Posts: 214
Location: Bellingham, WA

Posted: Tue Jul 20, 2010 7:05 pm Post subject: Re: Electrical Noise Prevention

 	  Quote: 	
		  Since you're not using a d-sub avionics ground, leave 

the 10AWG in place. 

	




Goodie!



Another person told me they'd expect noise if the P-leads are in the same bundle to the panel. That's how I've got them. But I don't have any audio system hooked up yet. Those wires would cross the P-leads or at a right angle.

_________________
Dan

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