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magneto wiring

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sarg314(at)comcast.net
Guest

Posted: Tue Apr 03, 2007 2:14 pm Post subject: magneto wiring

I just hooked up my magneto grounding wire (a shielded #1.  Checking 

with a continuity meter, there is continuity betwen the mag ground 

terminal and the P-lead regardless of whether the switch is open or 

closed or even disconnected, for that matter.  I'm concluding from this 

that the 2 terminals on the mag are connected internally through some 

coil, so the continuity test doesn't show what I was expecting.



Is this correct?



--

Tom S.

RV-6A, wiring.

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mprather(at)spro.net
Guest

Posted: Tue Apr 03, 2007 3:08 pm Post subject: magneto wiring

Yep.



A buzzbox detects the difference in inductance between shorted to ground

via the points when the points are closed (L=0), and shorted to ground via

the primary winding in the coil when the points are open.

Matt-



 	  Quote: 	
		   



 I just hooked up my magneto grounding wire (a shielded #1.  Checking

 with a continuity meter, there is continuity betwen the mag ground

 terminal and the P-lead regardless of whether the switch is open or

 closed or even disconnected, for that matter.  I'm concluding from this

 that the 2 terminals on the mag are connected internally through some

 coil, so the continuity test doesn't show what I was expecting.



 Is this correct?



 --

 Tom S.

 RV-6A, wiring.

- The Matronics AeroElectric-List Email Forum -

Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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nuckollsr(at)cox.net
Guest

Posted: Tue Apr 03, 2007 3:17 pm Post subject: magneto wiring

At 03:12 PM 4/3/2007 -0700, you wrote:



 	  Quote: 	
		  



I just hooked up my magneto grounding wire (a shielded #1.  Checking 

with a continuity meter, there is continuity betwen the mag ground 

terminal and the P-lead regardless of whether the switch is open or closed 

or even disconnected, for that matter.  I'm concluding from this that the 

2 terminals on the mag are connected internally through some coil, so the 

continuity test doesn't show what I was expecting.



Is this correct?


	


    The p-lead is connected across the PRIMARY winding

    of the magneto coil which has a very low resistance.

    Further, the timing points inside the magneto are

    connected in parallel with the magneto switch

    so even if the primary winding had some significant

    resistance, your ohmmeter check would still read VERY

    low if the points were closed.



    This is why an ohmmeter cannot be used as a practical

    tool for timing a magneto . . . it's exceedingly

    difficult to deduce when the points open based purely

    upon the DC resistance one observes from the outside

    looking in. This is why you use a "buzz box". The

    buzzer in a buzz-box generates a sort of AC signal

    that IS NOT highly loaded by the AC impedance of the

    magneto coil primary but IS severely loaded by closed

    points.



    Modern solid-state replacements for the century old

    buzz box use electronics to generate an

    AC signal needed to bias the magneto primary so

    that transitions of conductivity across the points

    may be readily detected during a timing operation.



        Bob . . .



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

        ( IF one aspires to be "world class",  )

        ( what ever you do must be exercised   )

        ( EVERY day . . .                      )

        (                  R. L. Nuckolls III  )

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

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