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Magneto P leads

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dean.psiropoulos(at)veriz
Guest

Posted: Sun Jul 23, 2006 9:51 pm Post subject: Magneto P leads

I'm wondering about connecting the P leads at the magneto. Looking at the

top of the (Slick) magneto I removed the nut and star washer and found an

insulating fiber washer.  Looking under the washer, there is the threaded

stud which projects from a piece of white plastic that is in turn surrounded

by a shiny piece of metal that looks like a large nut.  My question has to

do with grounding the P lead out on magneto which is what lectric Bob

recommends for lowest system noise.  I assume that the fiber washer is there

to keep the P lead terminal from grounding the threaded stud to the "shiny

metal nut" that surrounds the plastic that the stud projects out of.  If so,

can I use two ring terminals on the coax, one with a much larger ring placed

under the fiber washer which will serve as the return grounding path and

then place a smaller ring terminal (connected to the other wire in the

coax)on top of the fiber washer (which is on top of the larger ring terminal

contacting the shiny metal nut) under the nut that goes on the stud and not

have to worry about magneto grounding somewhere else on the engine?  I'm

just trying to not have to strip a whole bunch of shield off the P lead for

grounding at a separate location and this looks like it should work but I

know nothing about magnetos so I'm not sure if my hypothesis is correct.  I

hope you can decipher what I trying to say.  Thanks.



Dean Psiropoulos

RV-6A N197DM

Stringing wire (still)

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FLYaDIVE(at)aol.com
Guest

Posted: Mon Jul 24, 2006 5:00 am Post subject: Magneto P leads

In a message dated 7/24/06 1:55:30 AM Eastern Daylight Time, 

dean.psiropoulos(at)verizon.net writes:

[sniped]

 	  Quote: 	
		   My question has to

  do with grounding the P lead out on magneto which is what lectric Bob

  recommends for lowest system noise.  I assume that the fiber washer is 

there
	


 	  Quote: 	
		    to keep the P lead terminal from grounding the threaded stud to the "shiny

  metal nut" that surrounds the plastic that the stud projects out of.  If 

so,
	


 	  Quote: 	
		    can I use two ring terminals on the coax, one with a much larger ring 

placed
	


 	  Quote: 	
		    under the fiber washer which will serve as the return grounding path and

  then place a smaller ring terminal (connected to the other wire in the

  coax)on top of the fiber washer (which is on top of the larger ring 

terminal
	


 	  Quote: 	
		    contacting the shiny metal nut) under the nut that goes on the stud and not

  have to worry about magneto grounding somewhere else on the engine?  I'm

  just trying to not have to strip a whole bunch of shield off the P lead for

  grounding at a separate location and this looks like it should work but I

  know nothing about magnetos so I'm not sure if my hypothesis is correct.  I

  hope you can decipher what I trying to say.  Thanks.

  

  Dean Psiropoulos

  RV-6A N197DM

  Stringing wire (still) 

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


Dean:



Simple answer is NO!



DO NOT TOUCH THE FIBER WASHER OF THE MAG.

You will be sorry ... Very sorry.



There is a Ground screw not very far from the Fiber washer - Use that. That 

ground screw is for the Shield.



I don't know how you can ground the 'P' Lead anywhere else than at the Mag 

Switch.

Sure you could install a relay or solid-state device under the cowl right 

next to the Mag to keep your leads short but the simple and what I feel is the 

proper solution is just to use basic mil-spec shielded wire ... Connect the 

center lead to the center screw of the Mag and the shielded lead to the case 

ground.  YES, you are correct, keep the exposed/stripped wires as short as 

possible.  BUT!  Don't stress the wires.

The other end of the shielded wire is connected to the Mag Switch(s).  The 

Switch(s) in the RUN position OPENS the Ground between the center lead and the 

Ground side of the Mag Switch(s).  The shielded wire is there for noise 

suppression.  It is grounded at BOTH ends, Mag and Switch(s).



Maybe I'm getting word picky but you do not STRIP the shielding from the wire.

You separate the shield and center conductor.  And there is a trick in doing 

that so that 'not a single shield wire strand becomes broken'.



Trick - It is called the BEAST trick.  

1 - Determine how much conductor and shield you will need so there is NO 

strain.  Of course short wires are better, but not so short that you have a broken 

wire and a Hot Mag.



2 - This is the hard part.  Remove the jacket from the wire - This is done by 

bending the wire back 90 to 180 Deg and NICKING the wire using a razor.  You 

do NOT need to cut down to the shield.  Nick the wire, bend it and the wire 

will do the rest of the job. Now remove the jacket.



3 - Get a sharp thin ~1/8" Dia. scribe - At the base of the exposed shield 

use the scribe to separate the shielding exposing the center conductor.  Work 

the shield back and away to so you can see 4x (times) the diameter of the center 

conductor.



4 - Bend the wire at the exposed area 180 Deg.



5 - Use the scribe to hook under the center conductor and pull the free end 

UP and OUT of the shield.



6 - You are done ... No Nick, No stray strands - No errors.  Finish the ends 

which ever way you wish.  Crimp on lugs are usually my choice.

Barry

"Chop'd Liver"



"Show them the first time, correct them the second time, kick them the third 

time." 

Yamashiada

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nuckollsr(at)cox.net
Guest

Posted: Mon Jul 24, 2006 8:54 am Post subject: Magneto P leads

At 01:39 AM 7/24/2006 -0400, you wrote:



 	  Quote: 	
		  

<dean.psiropoulos(at)verizon.net>



I'm wondering about connecting the P leads at the magneto. Looking at the

top of the (Slick) magneto I removed the nut and star washer and found an

insulating fiber washer.  Looking under the washer, there is the threaded

stud which projects from a piece of white plastic that is in turn surrounded

by a shiny piece of metal that looks like a large nut.  My question has to

do with grounding the P lead out on magneto which is what lectric Bob

recommends for lowest system noise.  I assume that the fiber washer is there

to keep the P lead terminal from grounding the threaded stud to the "shiny

metal nut" that surrounds the plastic that the stud projects out of.  If so,

can I use two ring terminals on the coax, one with a much larger ring placed

under the fiber washer which will serve as the return grounding path and

then place a smaller ring terminal (connected to the other wire in the

coax)on top of the fiber washer (which is on top of the larger ring terminal

contacting the shiny metal nut) under the nut that goes on the stud and not

have to worry about magneto grounding somewhere else on the engine?  I'm

just trying to not have to strip a whole bunch of shield off the P lead for

grounding at a separate location and this looks like it should work but I

know nothing about magnetos so I'm not sure if my hypothesis is correct.  I

hope you can decipher what I trying to say.  Thanks.


	


    I'm not familiar with all the variations on the magneto

    connection schemes . . . the safe thing to recommend is

    that you not disassemble the terminal assembly beyond

    the removal of a nut or screw intended to accept the p-lead

    connection.



    Most of my readers have reported reasonably handy screws

    either on the mag house (or they've gone all the way

    down to the magneto mounting studs) to find a handy

    ground for the p-lead shields.



    Getting long leads out from under a shield is pretty

    easy. See:



    http://aeroelectric.com/articles/shldwire/shldwire.html



    Bob . . .



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

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

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

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Mon Jul 24, 2006 5:04 pm Post subject: Magneto P leads

7/24/2006



Responding to an AeroElectric-List message previously posted by: "DEAN 

PSIROPOULOS" <dean.psiropoulos(at)verizon.net>



Hello Dean, I was pleased to see your question on the list. It shows that 

you have an inquisitive mind and are thinking, and it shows that you are 

willing to seek out additional information. Your question creates an 

opportunity for a bit of information to be exchanged that may benefit others 

as well.



On the case of your Slick magneto very near the P (primary coil) lead stud 

is a threaded hole. Beside this threaded hole are the raised letters GND. 

This is an abbreviation for the word GROUND.



When the magneto comes new from Slick there is a Phillips head machine screw 

threaded into this hole. The purpose of this screw is to provide for a 

grounding contact to the magneto case.



Accepted procedure is to comb out a length of shielding from the magneto end 

of the shielded P lead, twist the shield wires together, and crimp a ring 

terminal of the appropriate size on the end of the combed out and twisted 

together shield wires. The shield ring terminal is then fastened to the 

magneto case by the aforementioned GND screw.



The center lead of the P lead wire also gets a ring terminal crimped on to 

it and this ring terminal is fastened to the P lead stud such that it does 

not contact the magneto case in any way.



On the cockpit end of the P lead the shield and the center wire are 

connected to the terminals of a switch such that when the switch is in the 

OFF position the shield and the center wire are connected together. This 

grounds out the magneto back to its case and prevents it from sparking the 

spark plugs. When the ignition switch is in the ON position the shield wire 

and the center wire of the P lead are separated from each other and the 

magneto can spark the plugs when properly rotated.



The term P lead is a bit of a misnomer because the lead does not connect 

directly to the primary coil of the magneto. Instead the P lead connects to 

a stud coming out of a capacitor (sometimes called a condenser in the older 

manuals) in the primary coil circuitry. Also in the primary coil circuitry 

are the magneto points. The capacitor in this circuit serves to suppress 

arcing between the points when they are being opened. The stud on the end of 

the capacitor also serves as a convenient point to ground out the primary 

coil output via the P lead connection back to a switch as described above 

when one does not want the magneto to be firing the spark plugs.



Looking forward to your next question.



OC

<<I'm wondering about connecting the P leads at the magneto. Looking at the

top of the (Slick) magneto I removed the nut and star washer and found an

insulating fiber washer.  Looking under the washer, there is the threaded

stud which projects from a piece of white plastic that is in turn surrounded

by a shiny piece of metal that looks like a large nut.  My question has to

do with grounding the P lead out on magneto which is what lectric Bob

recommends for lowest system noise.  I assume that the fiber washer is there

to keep the P lead terminal from grounding the threaded stud to the "shiny

metal nut" that surrounds the plastic that the stud projects out of.  If so,

can I use two ring terminals on the coax, one with a much larger ring placed

under the fiber washer which will serve as the return grounding path and

then place a smaller ring terminal (connected to the other wire in the

coax)on top of the fiber washer (which is on top of the larger ring terminal

contacting the shiny metal nut) under the nut that goes on the stud and not

have to worry about magneto grounding somewhere else on the engine?  I'm

just trying to not have to strip a whole bunch of shield off the P lead for

grounding at a separate location and this looks like it should work but I

know nothing about magnetos so I'm not sure if my hypothesis is correct.  I

hope you can decipher what I trying to say.  Thanks. Dean Psiropoulos>>

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