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Electrical question - shielding

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altojazz35(at)earthlink.n
Guest

Posted: Fri Jul 18, 2008 9:56 pm Post subject: Electrical question - shielding

Here's the problem.  I am using a fuel gauge that is  connected to capacitance type probes.   When the engine is running,  (503 DCDI) the fuel gauge jumps around like crazy.  After much testing and  trouble shooting, I believe the problem is related to the fuel sender wires  running near the ignition kill wires and/or the tach wire.  When I move  part of the fuel sender wires a few inches away, the problem improves.  I'm  really not wanting to move the sender wires to the other side of the airplane to  give more space between the different wire types.  Before I do this (since  it would be a lot of work for a fix that's not 100% guaranteed), is there a  quick and easy way to shield the fuel sender wires?  Would this even  work?  Any help from the electricians in the group would be  appreciated.

  

 

   [quote][b]

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rowedenny

Joined: 09 Mar 2008
Posts: 338
Location: Western PA

Posted: Sat Jul 19, 2008 2:10 am Post subject: Electrical question - shielding

[quote] ---

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altojazz35(at)earthlink.n
Guest

Posted: Sat Jul 19, 2008 6:17 am Post subject: Electrical question - shielding

Thanks Denny.

  

 I was wondering if shielding the fuel sender wire would  work instead of shielding the ignition wire and if so, what can be purchased to  shield it?

  

 I don't want to mess with any other wires since I don't  have any problems with radio noise.  I just need a little distance between  the sender wire and the other wires that are bundled and running down the side  of the frame to the instrument panel.  The tach wire might be the culprit  as well so I would really just like to shield the sender wire without replacing  any wires or moving anything around.

  

 Is there shielding that can be purchased (or made) and  slipped over the existing wire?  The wire currently runs along with all the  other wires in a bundle which is doesn't like, but this makes for a cleaner  installation than having wires running up both sides of the fuselage.  If  the shielding won't work, then this will be my next step.  Moving half the  wire away from the bundle by about 2 inches made the problem improve by at least  40%.  The capacitance system must be very sensitive to other electrical  fields.

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R. Hankins

Joined: 18 Jan 2006
Posts: 185
Location: Grants Pass, Oregon

Posted: Sat Jul 19, 2008 12:26 pm Post subject: Re: Electrical question - shielding

McMaster-Carr has what you need. Go to their website and search for part number: This stuff is a little spendy, but works great.

7940K31 



Emi/RFI-Shield Polyurethane Wraparound Sleeve 3/8" ID, Up to 3/8" Bundle Dia 

In stock

 

Quantity Per Ft. 

1-24 Ft. $7.00 

25 or more 5.50 



If the above is too expensive, do a search for braided sleeving.  They have several diameters of tinned copper braid.  Some of the ultralight places sell similar wire braid for shielding spark plug wires.

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_________________
Roger in Oregon
1992 KXP 503 - N1782C

herbgh(at)nctc.com
Guest

Posted: Sat Jul 19, 2008 12:46 pm Post subject: Electrical question - shielding

If you are frugal like me...then rescue some RG-8 coax from the 

salvage yard and pull the braided shield..Easy enough since it 

expands when collapsed...most of the connectors would have to be 

removed from the wire bundle...  however....Herb

At 03:26 PM 7/19/2008, you wrote:

 	  Quote: 	
		  



McMaster-Carr has what you need. Go to their website and search for 

part number: This stuff is a little spendy, but works great.

7940K31



Emi/RFI-Shield Polyurethane Wraparound Sleeve 3/8" ID, Up to 3/8" Bundle Dia

In stock



Quantity Per Ft.

1-24 Ft. $7.00

25 or more 5.50



If the above is too expensive, do a search for braided 

sleeving.  They have several diameters of tinned copper braid.  Some 

of the ultralight places sell similar wire braid for shielding spark 

plug wires.



--------

Roger in Oregon

1992 KXP 503 - N1782C





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=193809#193809

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WhiskeyVictor36(at)aol.co
Guest

Posted: Sat Jul 19, 2008 7:59 pm Post subject: Electrical question - shielding

In a message dated 7/19/2008 10:17:38 A.M. Eastern Daylight Time,  altojazz35(at)earthlink.net writes:

  	  Quote: 	
		     I was wondering if shielding the fuel sender wire would    work instead of shielding the ignition wire and if so, what can be purchased    to shield it?

    

   Would a wrapping of aluminum tin foil be of any help?     Just as a trial fix.     

   Bill    Varnes

Original Kolb FireStar

Audubon NJ

Do Not    Archive



	




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  [quote][b]

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altojazz35(at)earthlink.n
Guest

Posted: Sun Jul 20, 2008 12:40 am Post subject: Electrical question - shielding

> Would a wrapping of aluminum  tin foil be of any help?   Just as a trial fix.   



Bill  Varnes

Original Kolb FireStar

Audubon NJ

Do  Not  Archive

  

  

 ------------------------------

  

 I was thinking the same  thing but I have some aluminum foil tape that would be perfect.  It's the  same stuff you use on furnace exhaust vents.  Just like aluminum foil but  with and adhesive backing.  I'll give that a try tomorrow when I go to the  field.  The tape can be removed easily but also will stay in place if it  works well.  If it does seem to work, are there any drawbacks to using  aluminum foil tape compared to a braided sheath in terms of  effectiveness?

 



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rowedenny

Joined: 09 Mar 2008
Posts: 338
Location: Western PA

Posted: Sun Jul 20, 2008 6:41 pm Post subject: Electrical question - shielding

Mike,

I would try one of Rogers suggestions below if you don't want to disturb the 

kill switch wiring, just have to tie one end of the shielding to a good 

ground.

Let us know your results.

As long as thr fuel senders wires are shielded, the kill switch RFI should 

not affect your reading.



Denny



 	  Quote: 	
		   McMaster-Carr has what you need. Go to their website and search for part 

 number: This stuff is a little spendy, but works great.

 7940K31



 Emi/RFI-Shield Polyurethane Wraparound Sleeve 3/8" ID, Up to 3/8" Bundle 

 Dia

 In stock



 Quantity Per Ft.

 1-24 Ft. $7.00

 25 or more 5.50



 If the above is too expensive, do a search for braided sleeving.  They 

 have several diameters of tinned copper braid.  Some of the ultralight 

 places sell similar wire braid for shielding spark plug wires.



 --------

 Roger in Oregon

 1992 KXP 503 - N1782C

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altojazz35(at)earthlink.n
Guest

Posted: Sun Jul 20, 2008 7:37 pm Post subject: Electrical question - shielding

-- As long as the fuel senders wires are shielded, the  kill switch RFI should 

not affect your reading.

  

 Thanks for all the suggestions.  I have  good and bad news after working on the airplane.  The bad news is that the  shielding did nothing.  The good news is that the problem has nothing to do  with the shielding or interference.  My senders are bad.  I guess  that's more bad news.  I started thinking about the problem and realized  this was a problem that gradually appeared.  It happed slowly over such a  long period of time that I just thought it has always been a problem.  I'm  only 36 and my memory is already starting to go.  The senders use to work  fine when I initial installed them.  The vibration from the airplane is the  cause.  I found that at 2500 RPM I could get the gauges to work fine.   If I tapped on the sender the things went crazy.  I guess it's time to  contact the company and maybe order new ones.

 



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